Nudix hydrolase 23 post-translationally regulates carotenoid biosynthesis in plants.

Carotenoids are essential for photosynthesis and photoprotection. Plants must evolve multifaceted regulatory mechanisms to control carotenoid biosynthesis. However, the regulatory mechanisms and the regulators conserved among plant species remain elusive. Phytoene synthase (PSY) catalyzes the highly regulated step of carotenogenesis and geranylgeranyl diphosphate synthase (GGPPS) acts as a hub to interact with GGPP-utilizing enzymes for the synthesis of specific downstream isoprenoids. Here, we report a function of Nudix hydrolase 23 (NUDX23), a Nudix domain-containing protein, in post-translational regulation of PSY and GGPPS for carotenoid biosynthesis. NUDX23 expresses highly in Arabidopsis (Arabidopsis thaliana) leaves. Overexpression of NUDX23 significantly increases PSY and GGPPS protein levels and carotenoid production, whereas knockout of NUDX23 dramatically reduces their abundances and carotenoid accumulation in Arabidopsis. NUDX23 regulates carotenoid biosynthesis via direct interactions with PSY and GGPPS in chloroplasts, which enhances PSY and GGPPS protein stability in a large PSY-GGPPS enzyme complex. NUDX23 was found to co-migrate with PSY and GGPPS proteins and to be required for the enzyme complex assembly. Our findings uncover a regulatory mechanism underlying carotenoid biosynthesis in plants and offer promising genetic tools for developing carotenoid-enriched food crops.

Carotenoid sequestration protein FIBRILLIN participates in CmOR-regulated ß-carotene accumulation in melon.

Chromoplasts are plant organelles with a unique ability to sequester and store massive carotenoids. Chromoplasts have been hypothesized to enable high levels of carotenoid accumulation due to enhanced sequestration ability or sequestration substructure formation. However, the regulators that control the substructure component accumulation and substructure formation in chromoplasts remain unknown. In melon (Cucumis melo) fruit, ß-carotene accumulation in chromoplasts is governed by ORANGE (OR), a key regulator for carotenoid accumulation in chromoplasts. By using comparative proteomic analysis of a high ß-carotene melon variety and its isogenic line low-ß mutant that is defective in CmOr with impaired chromoplast formation, we identified carotenoid sequestration protein FIBRILLIN1 (CmFBN1) as differentially expressed. CmFBN1 expresses highly in melon fruit tissue. Overexpression of CmFBN1 in transgenic Arabidopsis (Arabidopsis thaliana) containing ORHis that genetically mimics CmOr significantly enhances carotenoid accumulation, demonstrating its involvement in CmOR-induced carotenoid accumulation. Both in vitro and in vivo evidence showed that CmOR physically interacts with CmFBN1. Such an interaction occurs in plastoglobules and results in promoting CmFBN1 accumulation. CmOR greatly stabilizes CmFBN1, which stimulates plastoglobule proliferation and subsequently carotenoid accumulation in chromoplasts. Our findings show that CmOR directly regulates CmFBN1 protein levels and suggest a fundamental role of CmFBN1 in facilitating plastoglobule proliferation for carotenoid sequestration. This study also reveals an important genetic tool to further enhance OR-induced carotenoid accumulation in chromoplasts in crops.

Overexpression of native ORANGE (OR) and OR mutant protein in Chlamydomonas reinhardtii enhances carotenoid and ABA accumulation and increases resistance to abiotic stress.

The carotenoid content of plants can be increased by overexpression of the regulatory protein ORANGE (OR) or a mutant variant known as the 'golden SNP'. In the present study, a strong light-inducible promoter was used to overexpress either wild type CrOR (CrORWT) or a mutated CrOR (CrORHis) containing a single histidine substitution for a conserved arginine in the microalgae Chlamydomonas reinhardtii. Overexpression of CrORWT and CrORHis roughly doubled and tripled, respectively, the accumulation of several different carotenoids, including ß-carotene, α-carotene, lutein and violaxanthin in C. reinhardtii and upregulated the transcript abundance of nearly all relevant carotenoid biosynthetic genes. In addition, microscopic analysis revealed that the OR transgenic cells were larger than control cells and exhibited larger chloroplasts with a disrupted morphology. Moreover, both CrORWT and CrORHis cell lines showed increased tolerance to salt and paraquat stress. The levels of endogenous phytohormone abscisic acid (ABA) were also increased in CrORWT and CrORHis lines, not only in normal growth conditions but also in growth medium supplemented with salt and paraquat. Together these results offer new insights regarding the role of the native OR protein in regulating carotenoid biosynthesis and the accumulation of several carotenoids in microalgae, and establish a new functional role for OR to modulate oxidative stress tolerance potentially mediated by ABA.

Proteome profile changes during poly-hydroxybutyrate intracellular mobilization in gram positive Bacillus cereus tsu1.

BACKGROUND: Bacillus cereus is a bacterial species which grows efficiently on a wide range of carbon sources and accumulates biopolymer poly-hydroxybutyrate (PHB) up to 80% cell dry weight. PHB is an aliphatic polymer produced and stored intracellularly as a reservoir of carbon and energy, its mobilization is a key biological process for sporulation in Bacillus spp. Previously, B. cereus tsu1 was isolated and cultured on rapeseed cake substrate (RCS), with maximum of PHB accumulation reached within 12 h, and depleted after 48 h. Fore-spore and spore structure were observed after 24 h culture. RESULTS: Quantitative proteomic analysis of B. cereus tsu1 identified 2952 quantifiable proteins, and 244 significantly changed proteins (SCPs) in the 24 h:12 h pair of samples, and 325 SCPs in the 48 h:12 h pair of samples. Based on gene ontology classification analysis, biological processes enriched only in the 24 h:12 h SCPs include purine nucleotide metabolism, protein folding, metal ion homeostasis, response to stress, carboxylic acid catabolism, and cellular amino acid catabolism. The 48 h:12 h SCPs were enriched into processes including carbohydrate metabolism, protein metabolism, oxidative phosphorylation, and formation of translation ternary structure. A key enzyme for PHB metabolism, poly(R)-hydroxyalkanoic acid synthase (PhaC, KGT44865) accumulated significantly higher in 12 h-culture. Sporulation related proteins SigF and SpoEII were significantly higher in 24 h-samples. Enzymes for nitrate respiration and fermentation accumulated to the highest abundance level in 48 h-culture. CONCLUSIONS: Changes in proteome of B. cereus tsu1 during PHB intracellular mobilization were characterized in this study. The key enzyme PhaC for PHB synthesis increased significantly after 12 h-culture which supports the highest PHB accumulation at this time point. The protein abundance level of SpoIIE and SigF also increased, correlating with sporulation in 24 h-culture. Enzymes for nitrate respiration and fermentation were significantly induced in 48 h-culture which indicates the depletion of oxygen at this stage and carbon flow towards fermentative growth. Results from this study provide insights into proteome profile changes during PHB accumulation and reuse, which can be applied to achieve a higher PHB yield and to improve bacterial growth performance and stress resistance.

Arabidopsis OR proteins are the major posttranscriptional regulators of phytoene synthase in controlling carotenoid biosynthesis.

Carotenoids are indispensable natural pigments to plants and humans. Phytoene synthase (PSY), the rate-limiting enzyme in the carotenoid biosynthetic pathway, and ORANGE (OR), a regulator of chromoplast differentiation and enhancer of carotenoid biosynthesis, represent two key proteins that control carotenoid biosynthesis and accumulation in plants. However, little is known about the mechanisms underlying their posttranscriptional regulation. Here we report that PSY and OR family proteins [Arabidopsis thaliana OR (AtOR) and AtOR-like] physically interacted with each other in plastids. We found that alteration of OR expression in Arabidopsis exerted minimal effect on PSY transcript abundance. However, overexpression of AtOR significantly increased the amount of enzymatically active PSY, whereas an ator ator-like double mutant exhibited a dramatically reduced PSY level. The results indicate that the OR proteins serve as the major posttranscriptional regulators of PSY. The ator or ator-like single mutant had little effect on PSY protein levels, which involves a compensatory mechanism and suggests partial functional redundancy. In addition, modification of PSY expression resulted in altered AtOR protein levels, corroborating a mutual regulation of PSY and OR. Carotenoid content showed a correlated change with OR-mediated PSY level, demonstrating the function of OR in controlling carotenoid biosynthesis by regulating PSY. Our findings reveal a novel mechanism by which carotenoid biosynthesis is controlled via posttranscriptional regulation of PSY in plants.

Proteome Modification in Tomato Plants upon Long-Term Aluminum Treatment.

This study aimed to identify the aluminum (Al)-induced proteomes in tomato (Solanum lycopersicum, "Micro-Tom") after long-term exposure to the stress factor. Plants were treated in Magnavaca's solution (pH 4.5) supplemented with 7.5 µM Al(3+) ion activity over a 4 month period beginning at the emergence of flower buds and ending when the lower mature leaves started to turn yellow. Proteomes were identified using a 8-plex isobaric tags for relative and absolute quantification (iTRAQ) labeling strategy followed by a two-dimensional (high- and low-pH) chromatographic separation and final generation of tandem mass spectrometry (MS/MS) spectra of tryptic peptides on an LTQ-Orbitrap Elite mass spectrometer. Principal component analysis revealed that the Al-treatment had induced systemic alterations in the proteomes from roots and leaves but not seed tissues. The significantly changed root proteins were shown to have putative functions in Al(3+) ion uptake and transportation, root development, and a multitude of other cellular processes. Changes in the leaf proteome indicate that the light reaction centers of photosynthetic machinery are the primary targets of Al-induced stress. Embryo and seed-coat tissues derived from Al-treated plants were enriched with stress proteins. The biological processes involving these Al-induced proteins concur with the physiological and morphological changes, such as the disturbance of mineral homeostasis (higher contents of Al, P, and Fe and reduced contents of S, Zn, and Mn in Al-treated compared to nontreated plants) in roots and smaller sizes of roots and the whole plants. More importantly, the identified significant proteins might represent a molecular mechanism for plants to develop toward establishing the Al tolerance and adaptation mechanism over a long period of stress treatment.

Plastid ribosomal protein S5 is involved in photosynthesis, plant development, and cold stress tolerance in Arabidopsis.

Plastid ribosomal proteins are essential components of protein synthesis machinery and have diverse roles in plant growth and development. Mutations in plastid ribosomal proteins lead to a range of developmental phenotypes in plants. However, how they regulate these processes is not fully understood, and the functions of some individual plastid ribosomal proteins remain unknown. To identify genes responsible for chloroplast development, we isolated and characterized a mutant that exhibited pale yellow inner leaves with a reduced growth rate in Arabidopsis. The mutant (rps5) contained a missense mutation of plastid ribosomal protein S5 (RPS5), which caused a dramatically reduced abundance of chloroplast 16S rRNA and seriously impaired 16S rRNA processing to affect ribosome function and plastid translation. Comparative proteomic analysis revealed that the rps5 mutation suppressed the expression of a large number of core components involved in photosystems I and II as well as many plastid ribosomal proteins. Unexpectedly, a number of proteins associated with cold stress responses were greatly decreased in rps5, and overexpression of the plastid RPS5 improved plant cold stress tolerance. Our results indicate that RPS5 is an important constituent of the plastid 30S subunit and affects proteins involved in photosynthesis and cold stress responses to mediate plant growth and development.

Drought-Induced Leaf Proteome Changes in Switchgrass Seedlings.

Switchgrass (Panicum virgatum) is a perennial crop producing deep roots and thus highly tolerant to soil water deficit conditions. However, seedling establishment in the field is very susceptible to prolonged and periodic drought stress. In this study, a "sandwich" system simulating a gradual water deletion process was developed. Switchgrass seedlings were subjected to a 20-day gradual drought treatment process when soil water tension was increased to 0.05 MPa (moderate drought stress) and leaf physiological properties had expressed significant alteration. Drought-induced changes in leaf proteomes were identified using the isobaric tags for relative and absolute quantitation (iTRAQ) labeling method followed by nano-scale liquid chromatography mass spectrometry (nano-LC-MS/MS) analysis. Additionally, total leaf proteins were processed using a combinatorial library of peptide ligands to enrich for lower abundance proteins. Both total proteins and those enriched samples were analyzed to increase the coverage of the quantitative proteomics analysis. A total of 7006 leaf proteins were identified, and 257 (4% of the leaf proteome) expressed a significant difference (p < 0.05, fold change <0.6 or >1.7) from the non-treated control to drought-treated conditions. These proteins are involved in the regulation of transcription and translation, cell division, cell wall modification, phyto-hormone metabolism and signaling transduction pathways, and metabolic pathways of carbohydrates, amino acids, and fatty acids. A scheme of abscisic acid (ABA)-biosynthesis and ABA responsive signal transduction pathway was reconstructed using these drought-induced significant proteins, showing systemic regulation at protein level to deploy the respective mechanism. Results from this study, in addition to revealing molecular responses to drought stress, provide a large number of proteins (candidate genes) that can be employed to improve switchgrass seedling growth and establishment under soil drought conditions (Data are available via ProteomeXchange with identifier PXD004675).

A workflow for large-scale empirical identification of cell wall N-linked glycoproteins of tomato (Solanum lycopersicum) fruit by tandem mass spectrometry.

Glycosylation is a common PTM of plant proteins that impacts a large number of important biological processes. Nevertheless, the impacts of differential site occupancy and the nature of specific glycoforms are obscure. Historically, characterization of glycoproteins has been difficult due to the distinct physicochemical properties of the peptidyl and glycan moieties, the variable and dynamic nature of the glycosylation process, their heterogeneous nature, and the low relative abundance of each glycoform. In this study, we explore a new pipeline developed for large-scale empirical identification of N-linked glycoproteins of tomato fruit as part of our ongoing efforts to characterize the tomato secretome. The workflow presented involves a combination of lectin affinity, tryptic digestion, ion-pairing HILIC, and precursor ion-driven data-dependent MS/MS analysis with a script to facilitate the identification and characterization of occupied N-linked glycosylation sites. A total of 212 glycoproteins were identified in this study, in which 26 glycopeptides from 24 glycoproteins were successfully characterized in just one HILIC fraction. Further precursor ion discovery-based MS/MS and deglycosylation followed by high accuracy and resolution MS analysis were used to confirm the glycosylation sites and determine site occupancy rates. The workflow reported is robust and capable of producing large amounts of empirical data involving N-linked glycosylation sites and their associated glycoforms.

Proteomic analysis of chromoplasts from six crop species reveals insights into chromoplast function and development.

Chromoplasts are unique plastids that accumulate massive amounts of carotenoids. To gain a general and comparative characterization of chromoplast proteins, this study performed proteomic analysis of chromoplasts from six carotenoid-rich crops: watermelon, tomato, carrot, orange cauliflower, red papaya, and red bell pepper. Stromal and membrane proteins of chromoplasts were separated by 1D gel electrophoresis and analysed using nLC-MS/MS. A total of 953-2262 proteins from chromoplasts of different crop species were identified. Approximately 60% of the identified proteins were predicted to be plastid localized. Functional classification using MapMan bins revealed large numbers of proteins involved in protein metabolism, transport, amino acid metabolism, lipid metabolism, and redox in chromoplasts from all six species. Seventeen core carotenoid metabolic enzymes were identified. Phytoene synthase, phytoene desaturase, ζ-carotene desaturase, 9-cis-epoxycarotenoid dioxygenase, and carotenoid cleavage dioxygenase 1 were found in almost all crops, suggesting relative abundance of them among the carotenoid pathway enzymes. Chromoplasts from different crops contained abundant amounts of ATP synthase and adenine nucleotide translocator, which indicates an important role of ATP production and transport in chromoplast development. Distinctive abundant proteins were observed in chromoplast from different crops, including capsanthin/capsorubin synthase and fibrillins in pepper, superoxide dismutase in watermelon, carrot, and cauliflower, and glutathione-S-transferease in papaya. The comparative analysis of chromoplast proteins among six crop species offers new insights into the general metabolism and function of chromoplasts as well as the uniqueness of chromoplasts in specific crop species. This work provides reference datasets for future experimental study of chromoplast biogenesis, development, and regulation in plants.

Evidence of glucosinolates translocation from inflorescences to stems during postharvest storage of broccoli.

Broccoli is a vegetable appreciated by consumers for its nutritional properties, particularly for its high glucosinolate (GLS) content. However, broccoli shows a high rate of senescence during postharvest and the GLS content in inflorescences decreases sharply. Usually, postharvest studies on broccoli focus on inflorescences, ignoring the other tissues harvested such as the stems and main stalk. In this work, GLS metabolism in whole heads of broccoli (including inflorescences, small stems and stalk) was analysed during postharvest senescence. The content of GLS content, expression of GLS metabolic genes, and expression of GLS transport-associated genes were measured in the three parts of harvested broccoli. A marked decrease in the content of all GLSs was detected in inflorescences, but an increase in the stems and stalk. Also, decreased expressions of GLS biosynthesis and degradation genes were detected in all tissues analysed. On the other hand, an increase in the expression of one of the genes involved in GLS transport was observed. These results suggest that GLSs would be transported from inflorescences to stems during postharvest senescence. From a commercial point of view, broccoli stems are usually discarded and not used as food. However, the accumulation of GLSs in the stems is an important factor to consider when contemplating potential commercial use of this part of the plant.

Co-chaperoning of chlorophyll and carotenoid biosynthesis by ORANGE family proteins in plants.

Chlorophylls and carotenoids are essential photosynthetic pigments. Plants spatiotemporally coordinate the needs of chlorophylls and carotenoids for optimal photosynthesis and fitness in response to diverse environmental and developmental cues. However, how the biosynthesis pathways of these two pigments are coordinated, particularly at posttranslational level to allow rapid control, remains largely unknown. Here, we report that the highly conserved ORANGE (OR) family proteins coordinate both pathways via posttranslationally mediating the first committed enzyme in each pathway. We demonstrate that OR family proteins physically interact with magnesium chelatase subunit I (CHLI) in chlorophyll biosynthesis pathway in addition to phytoene synthase (PSY) in carotenoid biosynthesis pathway and concurrently stabilize CHLI and PSY enzymes. We show that loss of OR genes hinders both chlorophyll and carotenoid biosynthesis, limits light-harvesting complex assembly, and impairs thylakoid grana stacking in chloroplasts. Overexpression of OR safeguards photosynthetic pigment biosynthesis and enhances thermotolerance in both Arabidopsis and tomato plants. Our findings establish a novel mechanism by which plants coordinate chlorophyll and carotenoid biosynthesis and provide a potential genetic target to generate climate-resilient crops.

Comparative characterization of the glycosylation profiles of an influenza hemagglutinin produced in plant and insect hosts.

The main objective of this study was to characterize the N-linked glycosylation profiles of recombinant hemagglutinin (HA) proteins expressed in either insect or plant hosts, and to develop a mass spectrometry based workflow that can be used in quality control to assess batch-to-batch reproducibility for recombinant HA glycosylation. HA is a surface glycoprotein of the influenza virus that plays a key role in viral infectivity and pathogenesis. Characterization of the glycans for plant recombinant HA from the viral strain A/California/04/09 (H1N1) has not yet been reported. In this study, N-linked glycosylation patterns of the recombinant HAs from both insect and plant hosts were characterized by precursor ion scan-driven data-dependent analysis followed by high-resolution MS/MS analysis of the deglycosylated tryptic peptides. Five glycosylation sites (N11, N23, N276, N287, and N481) were identified containing high mannose type glycans in plant-expressed HAs, and complex type glycoforms for the insect-expressed HA. More than 95% site occupancy was observed for all glycosylation sites except N11, which was 60% occupied. Multiple-reaction monitoring based quantitation analysis was developed for each glycopeptide isoform and the quantitative results indicate that the Man(8) GlcNAc(2) is the dominant glycan for all sites in plant-expressed HAs. The relative abundance of the glycoforms at each specific glycosylation site and the relative quantitation for each glycoform among three HAs were determined. Few differences in the glycosylation profiles were detected between the two batches of plant HAs studied, but there were significant differences between the glycosylation patterns in the HAs generated in plant and insect expression hosts.

Laser capture of tomato pericarp tissues for microscale carotenoid analysis by supercritical fluid chromatography.

Plant organs and tissues are comprised of an array of cell types often superimposed on a gradient of developmental stages. As a result, the ability to analyze and understand the synthesis, metabolism, and accumulation of plant biomolecules requires improved methods for cell- and tissue-specific analysis. Tomato (Solanum lycopersicum) is the world's most valuable fruit crop and is an important source of health-promoting dietary compounds, including carotenoids. Furthermore, tomato possesses unique genetic activities at the cell and tissue levels, making it an ideal system for tissue- and cell-type analysis of important biochemicals. A sample preparation workflow was developed for cell-type-specific carotenoid analysis in tomato fruit samples. Protocols for hyperspectral imaging of tomato fruit samples, cryoembedding and sectioning of pericarp tissue, laser microdissection of specific cell types, metabolite extraction using cell wall digestion enzymes and pressure cycling, and carotenoid quantification by supercritical fluid chromatography were optimized and integrated into a working protocol. The workflow was applied to quantify carotenoids in the cuticle and noncuticle component of the tomato pericarp during fruit development from the initial ripening to full ripe stages. Carotenoids were extracted and quantified from cell volumes less than 10nL. This workflow for cell-type-specific metabolite extraction and quantification can be adapted for the analysis of diverse metabolites, cell types, and organisms.

Using single cell type proteomics to identify Al-induced proteomes in outer layer cells and interior tissues in the apical meristem/cell division regions of tomato root-tips.

Aluminum (Al) toxicity primarily targets the root tips, inhibiting root growth and function and leading to crop yield losses on acidic soils. Previously we reported using laser capture microdissection (LCM) proteomics to identify Al-induced proteins in the outer layer cells in the transitional zone of tomato root-tips. This study aims to further characterize Al-induced proteomic dynamics from the outer to interior tissues, thus providing a panoramic view reflecting Al resistance in the root tip as a whole in tomatoes. Three types of cells were isolated via LCM from the basal 350-400 µm (below cell elongation regions) of root tips using tomato (Solanum lycopersicum) 'Micro-Tom' plants. Type I and Type II were from Al-treated plants. Type I included cells of the outer three layers, i.e., the epidermis and cortex initials and the quiescent center (QC) in root apical meristem (RAM), and Type II possessed the interior tissues of the same region. Type III contained cells from the non-Al-treated root tips collected in the same region as Type I. Two tandem mass tag (TMT) proteomics analyses with three biological replicates for each sample type were conducted. The TMTexp1 (comparing Type I and Type II) identified 6575 quantifiable proteins and 178 different abundance proteins (DAPs). The TMTexp2 (comparing Type I and Type III) identified 7197 quantifiable proteins and 162 DAPs. Among all quantified proteins (7685) from the two TMT experiments, 6088 (79%) proteins, including 313 DAPs (92% of the 340 total), were identified in all tissues. A model reflecting the tissue-specific Al-resistance mechanism was proposed, in which the level of the citrate transporter MATE protein, involved in Al exclusion, accumulated to the highest level in the outer-layer cells but decreased toward the interior of root-tips (which concurs with the tissue-specific importance in Al resistance). Proteins for biosynthesis of ethylene and jasmonic acid, proteolytic enzymes, stress-responsive proteins, and cell wall modeling were affected by Al treatment, some in a cell type-specific manner. The KEGG metabolite pathways enriched with these DAPs changed depending on the cell types. This study demonstrated the advantage of using the tissue/cell-specific analysis for identifying proteins and their dynamic changes directly associated with Al resistance in the root-tip region. The proteomics datasets have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository (https://www.ebi.ac.uk/pride/) with the dataset identifier as PXD021994 under project title: Proteomics studies of outer and inner cellular layers of tomato root-tips for Al stress, Project DOI: 10.6019/ PXD021994; and PXD018234 under Project title: Al-induced root proteomics changes in stress-acclimated tomato plant, Project DOI: https://doi.org/10.6019/PXD018234. SIGNIFICANCE: This paper presents the method of using laser capture microdissection (LCM) to collect homogenous cell-type specific tissue samples from the outer layers and inner central regions of tomato root-tips. The tandem mass tag-proteomics analysis showed that the outer-layer cells expressed proteomes that were different from the inner tissues of Al-treated root-tips; proteins related to resistance/tolerance to Al toxicity were highly accumulated in the outer-layer cells. Furthermore, the Al-treated outer-layer cells expressed proteomes which were different from the non-Al treated counterpart cells. This study has provided the first dataset of proteins differentiating from the outer to inner layers of cells in Al-treated root-tips. It provided convincing experimental evidences demonstrating the single-cell type proteomics as a powerful analytical approach to identify Al tolerance mechanisms in plants. The analytical procedure of LCM-tandem mass tag-quantitative proteomics analysis has a broad application for proteomics analysis of spatially separated cells in complex tissues.

Biomarker discovery from the top down: Protein biomarkers for efficient virus transmission by insects (Homoptera: Aphididae) discovered by coupling genetics and 2-D DIGE.

Yellow dwarf viruses cause the most economically important virus diseases of cereal crops worldwide and are vectored by aphids. The identification of vector proteins mediating virus transmission is critical to develop sustainable virus management practices and to understand viral strategies for circulative movement in all insect vectors. Previously, we applied 2-D DIGE to an aphid filial generation 2 population to identify proteins correlated with the transmission phenotype that were stably inherited and expressed in the absence of the virus. In the present study, we examined the expression of the DIGE candidates in previously unstudied, field-collected aphid populations. We hypothesized that the expression of proteins involved in virus transmission could be clinically validated in unrelated, virus transmission-competent, field-collected aphid populations. All putative biomarkers were expressed in the field-collected biotypes, and the expression of nine of these aligned with the virus transmission-competent phenotype. The strong conservation of the expression of the biomarkers in multiple field-collected populations facilitates new and testable hypotheses concerning the genetics and biochemistry of virus transmission. Integration of these biomarkers into current aphid-scouting methodologies will enable rational strategies for vector control aimed at judicious use and development of precision pest control methods that reduce plant virus infection.

Multi-strategy engineering greatly enhances provitamin A carotenoid accumulation and stability in Arabidopsis seeds.

Staple grains with low levels of provitamin A carotenoids contribute to the global prevalence of vitamin A deficiency and therefore are the main targets for provitamin A biofortification. However, carotenoid stability during both seed maturation and postharvest storage is a serious concern for the full benefits of carotenoid biofortified grains. In this study, we utilized Arabidopsis as a model to establish carotenoid biofortification strategies in seeds. We discovered that manipulation of carotenoid biosynthetic activity by seed-specific expression of Phytoene synthase (PSY) increases both provitamin A and total carotenoid levels but the increased carotenoids are prone to degradation during seed maturation and storage, consistent with previous studies of provitamin A biofortified grains. In contrast, stacking with Orange (OR His ), a gene that initiates chromoplast biogenesis, dramatically enhances provitamin A and total carotenoid content and stability. Up to 65- and 10-fold increases of ß-carotene and total carotenoids, respectively, with provitamin A carotenoids composing over 63% were observed in the seeds containing OR His and PSY. Co-expression of Homogentisate geranylgeranyl transferase (HGGT) with OR His and PSY further increases carotenoid accumulation and stability during seed maturation and storage. Moreover, knocking-out of ß-carotene hydroxylase 2 (BCH2) by CRISPR/Cas9 not only potentially facilitates ß-carotene accumulation but also minimizes the negative effect of carotenoid over production on seed germination. Our findings provide new insights into various processes on carotenoid accumulation and stability in seeds and establish a multiplexed strategy to simultaneously target carotenoid biosynthesis, turnover, and stable storage for carotenoid biofortification in crop seeds. Supplementary Information: The online version contains supplementary material available at 10.1007/s42994-021-00046-1.

Comparative Proteomics of Root Apex and Root Elongation Zones Provides Insights into Molecular Mechanisms for Drought Stress and Recovery Adjustment in Switchgrass.

Switchgrass plants were grown in a Sandwich tube system to induce gradual drought stress by withholding watering. After 29 days, the leaf photosynthetic rate decreased significantly, compared to the control plants which were watered regularly. The drought-treated plants recovered to the same leaf water content after three days of re-watering. The root tip (1cm basal fragment, designated as RT1 hereafter) and the elongation/maturation zone (the next upper 1 cm tissue, designated as RT2 hereafter) tissues were collected at the 29th day of drought stress treatment, (named SDT for severe drought treated), after one (D1W) and three days (D3W) of re-watering. The tandem mass tags mass spectrometry-based quantitative proteomics analysis was performed to identify the proteomes, and drought-induced differentially accumulated proteins (DAPs). From RT1 tissues, 6156, 7687, and 7699 proteins were quantified, and 296, 535, and 384 DAPs were identified in the SDT, D1W, and D3W samples, respectively. From RT2 tissues, 7382, 7255, and 6883 proteins were quantified, and 393, 587, and 321 proteins DAPs were identified in the SDT, D1W, and D3W samples. Between RT1 and RT2 tissues, very few DAPs overlapped at SDT, but the number of such proteins increased during the recovery phase. A large number of hydrophilic proteins and stress-responsive proteins were induced during SDT and remained at a higher level during the recovery stages. A large number of DAPs in RT1 tissues maintained the same expression pattern throughout drought treatment and the recovery phases. The DAPs in RT1 tissues were classified in cell proliferation, mitotic cell division, and chromatin modification, and those in RT2 were placed in cell wall remodeling and cell expansion processes. This study provided information pertaining to root zone-specific proteome changes during drought and recover phases, which will allow us to select proteins (genes) as better defined targets for developing drought tolerant plants. The mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD017441.

The Al-induced proteomes of epidermal and outer cortical cells in root apex of cherry tomato 'LA 2710'.

This paper reports a laser capture microdissection-tandem mass tag-quantitative proteomics analysis of Al-sensitive cells in root tips. Cherry tomato (Solanum lycopersicum var. cerasiforme 'LA2710') seedlings were treated under 15 µM Al3+ activity for 13 d. Root-tip longitudinal fresh frozen tissue sections of 10 µm thickness were prepared. The Al-sensitive root zone and cells were determined using histochemical analysis of root-tips and micro-sections. A procedure for collecting the Al-sensitive cells using laser capture microdissection-protein extraction-tandem mass tag-proteomics analysis was developed. Proteomics analysis of 18 µg protein/sample with three biological replicates per treatment condition identified 3879 quantifiable proteins each associated with two or more unique peptides. Quantified proteins constituted a broad range of Kyoto Encyclopedia of Genes and Genomes pathways when searched in the annotated tomato genome. Differentially expressed proteins between the Al-treated and non-Al treated control conditions were identified, including 128 Al-up-regulated and 32 Al-down-regulated proteins. Analysis of functional pathways and protein-protein interaction networks showed that the Al-down-regulated proteins are involved in transcription and translation, and the Al-up-regulated proteins are associated with antioxidant and detoxification and protein quality control processes. The proteomics data are available via ProteomeXchange with identifier PXD010459 under project title 'LCM-quantitative proteomics analysis of Al-sensitive tomato root cells'. SIGNIFICANCE: This paper presents an efficient laser capture microdissection-tandem mass tag-quantitative proteomics analysis platform for the analysis of Al sensitive root cells. The analytical procedure has a broad application for proteomics analysis of spatially separated cells from complex tissues. This study has provided a comprehensive proteomics dataset expressed in the epidermal and outer-cortical cells at root-tip transition zone of Al-treated tomato seedlings. The proteomes from the Al-sensitive root cells are valuable resources for understanding and improving Al tolerance in plants.

Al-induced proteomics changes in tomato plants over-expressing a glyoxalase I gene.

Glyoxalase I (Gly I) is the first enzyme in the glutathionine-dependent glyoxalase pathway for detoxification of methylglyoxal (MG) under stress conditions. Transgenic tomato 'Money Maker' plants overexpressing tomato SlGlyI gene (tomato unigene accession SGN-U582631/Solyc09g082120.3.1) were generated and homozygous lines were obtained after four generations of self-pollination. In this study, SlGlyI-overepxressing line (GlyI), wild type (WT, negative control) and plants transformed with empty vector (ECtr, positive control), were subjected to Al-treatment by growing in Magnavaca's nutrient solution (pH 4.5) supplemented with 20 µM Al3+ ion activity. After 30 days of treatments, the fresh and dry weight of shoots and roots of plants from Al-treated conditions decreased significantly compared to the non-treated conditions for all the three lines. When compared across the three lines, root fresh and dry weight of GlyI was significant higher than WT and ECtr, whereas there was no difference in shoot tissues. The basal 5 mm root-tips of GlyI plants expressed a significantly higher level of glyoxalase activity under both non-Al-treated and Al-treated conditions compared to the two control lines. Under Al-treated condition, there was a significant increase in MG content in ECtr and WT lines, but not in GlyI line. Quantitative proteomics analysis using tandem mass tags mass spectrometry identified 4080 quantifiable proteins and 201 Al-induced differentially expressed proteins (DEPs) in root-tip tissues from GlyI, and 4273 proteins and 230 DEPs from ECtr. The Al-down-regulated DEPs were classified into molecular pathways of gene transcription, RNA splicing and protein biosynthesis in both GlyI and ECtr lines. The Al-induced DEPs in GlyI associated with tolerance to Al3+ and MG toxicity are involved in callose degradation, cell wall components (xylan acetylation and pectin degradation), oxidative stress (antioxidants) and turnover of Al-damaged epidermal cells, repair of damaged DNA, epigenetics, gene transcription, and protein translation. A protein-protein association network was constructed to aid the selection of proteins in the same pathway but differentially regulated in GlyI or ECtr lines. Proteomics data are available via ProteomeXchange with identifiers PXD009456 under project title '25Dec2017_Suping_XSexp2_ITAG3.2' for SlGlyI-overexpressing tomato plants and PXD009848 under project title '25Dec2017_Suping_XSexp3_ITAG3.2' for positive control ECtr line transformed with empty vector.