Rice LIKE EARLY STARVATION1 cooperates with FLOURY ENDOSPERM6 to modulate starch biosynthesis and endosperm development.

In cereal grains, starch is synthesized by the concerted actions of multiple enzymes on the surface of starch granules within the amyloplast. However, little is known about how starch-synthesizing enzymes access starch granules, especially for amylopectin biosynthesis. Here, we show that the rice (Oryza sativa) floury endosperm9 (flo9) mutant is defective in amylopectin biosynthesis, leading to grains exhibiting a floury endosperm with a hollow core. Molecular cloning revealed that FLO9 encodes a plant-specific protein homologous to Arabidopsis (Arabidopsis thaliana) LIKE EARLY STARVATION1 (LESV). Unlike Arabidopsis LESV, which is involved in starch metabolism in leaves, OsLESV is required for starch granule initiation in the endosperm. OsLESV can directly bind to starch by its C-terminal tryptophan (Trp)-rich region. Cellular and biochemical evidence suggests that OsLESV interacts with the starch-binding protein FLO6, and loss-of-function mutations of either gene impair ISOAMYLASE1 (ISA1) targeting to starch granules. Genetically, OsLESV acts synergistically with FLO6 to regulate starch biosynthesis and endosperm development. Together, our results identify OsLESV-FLO6 as a non-enzymatic molecular module responsible for ISA1 localization on starch granules, and present a target gene for use in biotechnology to control starch content and composition in rice endosperm.

MFP1 defines the subchloroplast location of starch granule initiation.

Starch is one of the major carbohydrate storage compounds in plants. The biogenesis of starch granules starts with the formation of initials, which subsequently expand into granules. Several coiled-coil domain-containing proteins have been previously implicated with the initiation process, but the mechanisms by which they act remain largely elusive. Here, we demonstrate that one of these proteins, the thylakoid-associated MAR-BINDING FILAMENT-LIKE PROTEIN 1 (MFP1), specifically determines the subchloroplast location of initial formation. The expression of MFP1 variants "mis"-targeted to specific locations within chloroplasts in Arabidopsis results in distinctive shifts in not only how many but also where starch granules are formed. Importantly, "re" localizing MFP1 to the stromal face of the chloroplast's inner envelope is sufficient to generate starch granules in this aberrant position. These findings provide compelling evidence that a single protein MFP1 possesses the capacity to direct the initiation and biosynthesis machinery of starch granules.

SAGA1 and SAGA2 promote starch formation around proto-pyrenoids in Arabidopsis chloroplasts.

The pyrenoid is a chloroplastic microcompartment in which most algae and some terrestrial plants condense the primary carboxylase, Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) as part of a CO2-concentrating mechanism that improves the efficiency of CO2 capture. Engineering a pyrenoid-based CO2-concentrating mechanism (pCCM) into C3 crop plants is a promising strategy to enhance yield capacities and resilience to the changing climate. Many pyrenoids are characterized by a sheath of starch plates that is proposed to act as a barrier to limit CO2 diffusion. Recently, we have reconstituted a phase-separated "proto-pyrenoid" Rubisco matrix in the model C3 plant Arabidopsis thaliana using proteins from the alga with the most well-studied pyrenoid, Chlamydomonas reinhardtii [N. Atkinson, Y. Mao, K. X. Chan, A. J. McCormick, Nat. Commun. 11, 6303 (2020)]. Here, we describe the impact of introducing the Chlamydomonas proteins StArch Granules Abnormal 1 (SAGA1) and SAGA2, which are associated with the regulation of pyrenoid starch biogenesis and morphology. We show that SAGA1 localizes to the proto-pyrenoid in engineered Arabidopsis plants, which results in the formation of atypical spherical starch granules enclosed within the proto-pyrenoid condensate and adjacent plate-like granules that partially cover the condensate, but without modifying the total amount of chloroplastic starch accrued. Additional expression of SAGA2 further increases the proportion of starch synthesized as adjacent plate-like granules that fully encircle the proto-pyrenoid. Our findings pave the way to assembling a diffusion barrier as part of a functional pCCM in vascular plants, while also advancing our understanding of the roles of SAGA1 and SAGA2 in starch sheath formation and broadening the avenues for engineering starch morphology.

The kiwifruit amyloplast proteome (kfALP): a resource to better understand the mechanisms underlying amyloplast biogenesis and differentiation.

The biogenesis and differentiation (B&D) of amyloplasts contributes to fruit flavor and color. Here, remodeling of starch granules, thylakoids and plastoglobules was observed during development and ripening in two kiwifruit (Actinidia spp.) cultivars - yellow-fleshed 'Hort16A' and green-fleshed 'Hayward'. A protocol was developed to purify starch-containing plastids with a high degree of intactness, and amyloplast B&D was studied using label-free-based quantitative proteomic analyses in both cultivars. Over 3000 amyloplast-localized proteins were identified, of which >98% were quantified and defined as the kfALP (kiwifruit amyloplast proteome). The kfALP data were validated by Tandem-Mass-Tag (TMT) labeled proteomics in 'Hort16A'. Analysis of the proteomic data across development and ripening revealed: 1) a conserved increase in the abundance of proteins participating in starch synthesis/degradation during both amyloplast B&D; 2) up-regulation of proteins for chlorophyll degradation and of plastoglobule-localized proteins associated with chloroplast breakdown and plastoglobule formation during amyloplast differentiation; 3) constitutive expression of proteins involved in ATP supply and protein import during amyloplast B&D. Interestingly, two different pathways of amyloplast B&D were observed in the two cultivars. In 'Hayward', significant increases in abundance of photosynthetic- and tetrapyrrole metabolism-related proteins were observed, but the opposite trend was observed in 'Hort16A'. In conclusion, analysis of the kfALP provides new insights into the potential mechanisms underlying amyloplast B&D with relevance to key fruit quality traits in contrasting kiwifruit cultivars.

Trehalose-6-phosphate synthase 8 increases photosynthesis and seed yield in Brassica napus.

Trehalose-6-phosphate (T6P) functions as a vital proxy for assessing carbohydrate status in plants. While class II T6P synthases (TPS) do not exhibit TPS activity, they are believed to play pivotal regulatory roles in trehalose metabolism. However, their precise functions in carbon metabolism and crop yield have remained largely unknown. Here, BnaC02.TPS8, a class II TPS gene, is shown to be specifically expressed in mature leaves and the developing pod walls of Brassica napus. Overexpression of BnaC02.TPS8 increased photosynthesis and the accumulation of sugars, starch, and biomass compared to wild type. Metabolomic analysis of BnaC02.TPS8 overexpressing lines and CRISPR/Cas9 mutants indicated that BnaC02.TPS8 enhanced the partitioning of photoassimilate into starch and sucrose, as opposed to glycolytic intermediates and organic acids, which might be associated with TPS activity. Furthermore, the overexpression of BnaC02.TPS8 not only increased seed yield but also enhanced seed oil accumulation and improved the oil fatty acid composition in B. napus under both high nitrogen (N) and low N conditions in the field. These results highlight the role of class II TPS in impacting photosynthesis and seed yield of B. napus, and BnaC02.TPS8 emerges as a promising target for improving B. napus seed yield.

Carbon usage in yellow-fleshed Manihot esculenta storage roots shifts from starch biosynthesis to cell wall and raffinose biosynthesis via the myo-inositol pathway.

Cassava is a crucial staple crop for smallholder farmers in tropical Asia and Sub-Saharan Africa. Although high yield remains the top priority for farmers, the significance of nutritional values has increased in cassava breeding programs. A notable negative correlation between provitamin A and starch accumulation poses a significant challenge for breeding efforts. The negative correlation between starch and carotenoid levels in conventional and genetically modified cassava plants implies the absence of a direct genomic connection between the two traits. The competition among various carbon pathways seems to account for this relationship. In this study, we conducted a thorough analysis of 49 African cassava genotypes with varying levels of starch and provitamin A. Our goal was to identify factors contributing to differential starch accumulation. Considering carotenoid levels as a confounding factor in starch production, we found that yellow- and white-fleshed storage roots did not differ significantly in most measured components of starch or de novo fatty acid biosynthesis. However, genes and metabolites associated with myo-inositol synthesis and cell wall polymer production were substantially enriched in high provitamin A genotypes. These results indicate that yellow-fleshed cultivars, in comparison to their white-fleshed counterparts, direct more carbon toward the synthesis of raffinose and cell wall components. This finding is underlined by a significant rise in cell wall components measured within the 20 most contrasting genotypes for carotenoid levels. Our findings enhance the comprehension of the biosynthesis of starch and carotenoids in the storage roots of cassava.

MaC2H2-IDD regulates fruit softening and involved in softening disorder induced by cold stress in banana.

Chilling stress causes banana fruit softening disorder and severely impairs fruit quality. Various factors, such as transcription factors, regulate fruit softening. Herein, we identified a novel regulator, MaC2H2-IDD, whose expression is closely associated with fruit ripening and softening disorder. MaC2H2-IDD is a transcriptional activator located in the nucleus. The transient and ectopic overexpression of MaC2H2-IDD promoted "Fenjiao" banana and tomato fruit ripening. However, transient silencing of MaC2H2-IDD repressed "Fenjiao" banana fruit ripening. MaC2H2-IDD modulates fruit softening by activating the promoter activity of starch (MaBAM3, MaBAM6, MaBAM8, MaAMY3, and MaISA2) and cell wall (MaEXP-A2, MaEXP-A8, MaSUR14-like, and MaGLU22-like) degradation genes. DLR, Y1H, EMSA, and ChIP-qPCR assays validated the expression regulation. MaC2H2-IDD interacts with MaEBF1, enhancing the regulation of MaC2H2-IDD to MaAMY3, MaEXP-A2, and MaGLU22-like. Overexpressing/silencing MaC2H2-IDD in banana and tomato fruit altered the transcript levels of the cell wall and starch (CWS) degradation genes. Several differentially expressed genes (DEGs) were authenticated between the overexpression and control fruit. The DEGs mainly enriched biosynthesis of secondary metabolism, amino sugar and nucleotide sugar metabolism, fructose and mannose metabolism, starch and sucrose metabolism, and plant hormones signal transduction. Overexpressing MaC2H2-IDD also upregulated protein levels of MaEBF1. MaEBF1 does not ubiquitinate or degrade MaC2H2-IDD. These data indicate that MaC2H2-IDD is a new regulator of CWS degradation in "Fenjiao" banana and cooperates with MaEBF1 to modulate fruit softening, which also involves the cold softening disorder.

Molecular mechanisms underlying low temperature inhibition of grain filling in maize (Zea mays L.): coordination of growth and cold responses.

Low temperature (LT) greatly restricts grain filling in maize (Zea mays L.), but the relevant molecular mechanisms are not fully understood. To better understand the effect of LT on grain development, 17 hybrids were subjected to LT stress in field trials over 3 years, and two hybrids of them with contrasting LT responses were exposed to 30/20°C and 20/10°C for 7 days during grain filling in a greenhouse. At LT, thousand-kernel weight declined, especially in LT-sensitive hybrid FM985, while grain-filling rate was on average about 48% higher in LT-tolerant hybrid DK159 than FM985. LT reduced starch synthesis in kernel mainly by suppression of transcript levels and enzyme activities for sucrose synthase and hexokinase. Brassinolide (BR) was abundant in DK159 kernel, and genes involved in BR and cytokinin signals were inducible by stress. LT downregulated the genes in light-harvesting complex and photosystem I/II subunits, accompanied by reduced photosynthetic rate and Fv/Fm in ear leaf. The LT-tolerant hybrid could maintain a high soluble sugar content and fast interconversion between sucrose and hexose in the stem internode and cob, improving assimilate allocation to kernel at LT stress and paving the way for simultaneous growth and LT stress responses.

Regulatory loops between rice transcription factors OsNAC25 and OsNAC20/26 balance starch synthesis.

Several starch synthesis regulators have been identified, but these regulators are situated in the terminus of the regulatory network. Their upstream regulators and the complex regulatory network formed between these regulators remain largely unknown. A previous study demonstrated that NAM, ATAF, and CUC (NAC) transcription factors, OsNAC20 and OsNAC26 (OsNAC20/26), redundantly and positively regulate the accumulation of storage material in rice (Oryza sativa) endosperm. In this study, we detected OsNAC25 as an upstream regulator and interacting protein of OsNAC20/26. Both OsNAC25 mutation and OE resulted in a chalky seed phenotype, decreased starch content, and reduced expression of starch synthesis-related genes, but the mechanisms were different. In the osnac25 mutant, decreased expression of OsNAC20/26 resulted in reduced starch synthesis; however, in OsNAC25-overexpressing plants, the OsNAC25-OsNAC20/26 complex inhibited OsNAC20/26 binding to the promoter of starch synthesis-related genes. In addition, OsNAC20/26 positively regulated OsNAC25. Therefore, the mutual regulation between OsNAC25 and OsNAC20/26 forms a positive regulatory loop to stimulate the expression of starch synthesis-related genes and meet the great demand for starch accumulation in the grain filling stage. Simultaneously, a negative regulatory loop forms among the 3 proteins to avoid the excessive expression of starch synthesis-related genes. Collectively, our findings demonstrate that both promotion and inhibition mechanisms between OsNAC25 and OsNAC20/26 are essential for maintaining stable expression of starch synthesis-related genes and normal starch accumulation.

LIKE EARLY STARVATION 1 interacts with amylopectin during starch biosynthesis.

Starch is the major energy storage compound in plants. Both transient starch and long-lasting storage starch accumulate in the form of insoluble, partly crystalline granules. The structure of these granules is related to the structure of the branched polymer amylopectin: linear chains of glucose units organized in double helices that align to form semicrystalline lamellae, with branching points located in amorphous regions between them. EARLY STARVATION 1 (ESV1) and LIKE EARLY STARVATION 1 (LESV) proteins are involved in the maintenance of starch granule structure and in the phase transition of amylopectin, respectively, in Arabidopsis (Arabidopsis thaliana). These proteins contain a conserved tryptophan-rich C-terminal domain folded into an antiparallel ß-sheet, likely responsible for binding of the proteins to starch, and different N-terminal domains whose structure and function are unknown. In this work, we combined biochemical and biophysical approaches to analyze the structures of LESV and ESV1 and their interactions with the different starch polyglucans. We determined that both proteins interact with amylopectin but not with amylose and that only LESV is capable of interacting with amylopectin during starch biosynthesis. While the C-terminal domain interacts with amylopectin in its semicrystalline form, the N-terminal domain of LESV undergoes induced conformational changes that are probably involved in its specific function of mediating glucan phase transition. These results clarify the specific mechanism of action of these 2 proteins in the biosynthesis of starch granules.

Auxin receptor OsTIR1 mediates auxin signaling during seed filling in rice.

Cereal endosperm represents the most important source of the world's food. Nevertheless, the molecular mechanisms behind sugar import into rice (Oryza sativa) endosperm and their relationship with auxin signaling are poorly understood. Here, we report that auxin transport inhibitor response 1 (TIR1) plays an essential role in rice grain yield and quality via modulating sugar transport into endosperm. The fluctuations of OsTIR1 transcripts parallel to the early stage of grain expansion among those of the 5 TIR1/AFB (auxin-signaling F-box) auxin co-receptor proteins. OsTIR1 is abundantly expressed in ovular vascular trace, nucellar projection, nucellar epidermis, aleurone layer cells, and endosperm, providing a potential path for sugar into the endosperm. Compared to wild-type (WT) plants, starch accumulation is repressed by mutation of OsTIR1 and improved by overexpression of the gene, ultimately leading to reduced grain yield and quality in tir1 mutants but improvement in overexpression lines. Of the rice AUXIN RESPONSE FACTOR (ARF) genes, only the OsARF25 transcript is repressed in tir1 mutants and enhanced by overexpression of OsTIR1; its highest transcript is recorded at 10 d after fertilization, consistent with OsTIR1 expression. Also, OsARF25 can bind the promoter of the sugar transporter OsSWEET11 (SWEET, sugars will eventually be exported transporter) in vivo and in vitro. arf25 and arf25/sweet11 mutants exhibit reduced starch content and seed size (relative to the WTs), similar to tir1 mutants. Our data reveal that OsTIR1 mediates sugar import into endosperm via the auxin signaling component OsARF25 interacting with sugar transporter OsSWEET11. The results of this study are of great significance to further clarify the regulatory mechanism of auxin signaling on grain development in rice.

Wheat-Based Glues in Conservation and Cultural Heritage: (Dis)solving the Proteome of Flour and Starch Pastes and Their Adhering Properties.

Plant-based adhesives, such as those made from wheat, have been prominently used for books and paper-based objects and are also used as conservation adhesives. Starch paste originates from starch granules, whereas flour paste encompasses the entire wheat endosperm proteome, offering strong adhesive properties due to gluten proteins. From a conservation perspective, understanding the precise nature of the adhesive is vital as the longevity, resilience, and reaction to environmental changes can differ substantially between starch- and flour-based pastes. We devised a proteomics method to discern the protein content of these pastes. Protocols involved extracting soluble proteins using 0.5 M NaCl and 30 mM Tris-HCl solutions and then targeting insoluble proteins, such as gliadins and glutenins, with a buffer containing 7 M urea, 2 M thiourea, 4% CHAPS, 40 mM Tris, and 75 mM DTT. Flour paste's proteome is diverse (1942 proteins across 759 groups), contrasting with starch paste's predominant starch-associated protein makeup (218 proteins in 58 groups). Transformation into pastes reduces proteomes' complexity. Testing on historical bookbindings confirmed the use of flour-based glue, which is rich in gluten and serpins. High levels of deamidation were detected, particularly for glutamine residues, which can impact the solubility and stability of the glue over time. The mass spectrometry proteomics data have been deposited to the ProteomeXchange, Consortium (http://proteomecentral.proteomexchange.org) via the MassIVE partner repository with the data set identifier MSV000093372 (ftp://MSV000093372@massive.ucsd.edu).

Structural basis for the recognition of α-1,6-branched α-glucan by GH13_47 α-amylase from Rhodothermus marinus.

Glycoside hydrolase (GH) family 13 is among the main families of enzymes acting on starch; recently, subfamily 47 of GH13 (GH13_47) has been established. The crystal structure and function of a GH13_47 enzyme from Bacteroides ovatus has only been reported to date. This enzyme has α-amylase activity, while the GH13_47 enzymes comprise approximately 800-900 amino acid residues which are almost double those of typical α-amylases. It is important to know how different the GH13_47 enzymes are from other α-amylases. Rhodothermus marinus JCM9785, a thermophilic bacterium, possesses a gene for the GH13_47 enzyme, which is designated here as RmGH13_47A. Its structure has been predicted to be composed of seven domains: N1, N2, N3, A, B, C, and D. We constructed a plasmid encoding Gly266-Glu886, which contains the N3, A, B, and C domains and expressed the protein in Escherichia coli. The enzyme hydrolyzed starch and pullulan by a neopullulanase-type action. Additionally, the enzyme acted on maltotetraose, and saccharides with α-1,6-glucosidic linkages were observed in the products. Following the replacement of the catalytic residue Asp563 with Ala, the crystal structure of the variant D563A in complex with the enzymatic products from maltotetraose was determined; as a result, electron density for an α-1,6-branched pentasaccharide was observed in the catalytic pocket, and Ile762 and Asp763 interacted with the branched chain of the pentasaccharide. These findings suggest that RmGH13_47A is an α-amylase that prefers α-1,6-branched parts of starch to produce oligosaccharides.

Whole-genome sequencing and comparative genomics reveal candidate genes associated with quality traits in Dioscorea alata.

BACKGROUND: Quality traits are essential determinants of consumer preferences. Dioscorea alata (Greater Yam), is a starchy tuber crop in tropical regions. However, a comprehensive understanding of the genetic basis underlying yam tuber quality remains elusive. To address this knowledge gap, we employed population genomics and candidate gene association approaches to unravel the genetic factors influencing the quality attributes of boiled yam. METHODS AND RESULTS: Comparative genomics analysis of 45 plant species revealed numerous novel genes absent in the existing D. alata gene annotation. This approach, adding 48% more genes, significantly enhanced the functional annotation of three crucial metabolic pathways associated with boiled yam quality traits: pentose and glucuronate interconversions, starch and sucrose metabolism, and flavonoid biosynthesis. In addition, the whole-genome sequencing of 127 genotypes identified 27 genes under selection and 22 genes linked to texture, starch content, and color through a candidate gene association analysis. Notably, five genes involved in starch content and cell wall composition, including 1,3-beta Glucan synthase, ß-amylase, and Pectin methyl esterase, were common to both approaches and their expression levels were assessed by transcriptomic data. CONCLUSIONS: The analysis of the whole-genome of 127 genotypes of D. alata and the study of three specific pathways allowed the identification of important genes for tuber quality. Our findings provide insights into the genetic basis of yam quality traits and will help the enhancement of yam tuber quality through breeding programs.

Allelic variation in the autotetraploid potato: genes involved in starch and steroidal glycoalkaloid metabolism as a case study.

BACKGROUND: Tuber starch and steroidal glycoalkaloid (SGA)-related traits have been consistently prioritized in potato breeding, while allelic variation pattern of genes that underlie these traits is less explored. RESULTS: Here, we focused on the genes involved in two important metabolic pathways in the potato: starch metabolism and SGA biosynthesis. We identified 119 genes consisting of 81 involved in starch metabolism and 38 in the biosynthesis of steroidal glycoalkaloids, and discovered 96,166 allelic variants among 2,169 gene haplotypes in six autotetraploid potato genomes. Comparative analyses revealed an uneven distribution of allelic variants among gene haplotypes and that the vast majority of deleterious mutations in these genes are retained in heterozygous state in the autotetraploid potato genomes. Leveraging full-length cDNA sequencing data, we find that approximately 70% of haplotypes of the 119 genes are transcribable. Population genetic analyses identify starch and SGA biosynthetic genes that are potentially conserved or diverged between potato varieties with varying starch or SGA content. CONCLUSIONS: These results deepen the understanding of haplotypic diversity within functionally important genes in autotetraploid genomes and may facilitate functional characterization of genes or haplotypes contributing to traits related to starch and SGA in potato.

Multi-omic analysis reveals the effects of interspecific hybridization on the synthesis of seed reserve polymers in a Triticum turgidum ssp. durum × Aegilops sharonensis amphidiploid.

BACKGROUND: Wheat grain endosperm is mainly composed of proteins and starch. The contents and the overall composition of seed storage proteins (SSP) markedly affect the processing quality of wheat flour. Polyploidization results in duplicated chromosomes, and the genomes are often unstable and may result in a large number of gene losses and gene rearrangements. However, the instability of the genome itself, as well as the large number of duplicated genes generated during polyploidy, is an important driving force for genetic innovation. In this study, we compared the differences in starch and SSP, and analyzed the transcriptome and metabolome among Aegilops sharonensis (R7), durum wheat (Z636) and amphidiploid (Z636×R7) to reveal the effects of polyploidization on the synthesis of seed reserve polymers. RESULTS: The total starch and amylose content of Z636×R7 was significantly higher than R7 and lower than Z636. The gliadin and glutenin contents of Z636×R7 were higher than those in Z636 and R7. Through transcriptome analysis, there were 21,037, 2197, 15,090 differentially expressed genes (DEGs) in the three comparison groups of R7 vs Z636, Z636 vs Z636×R7, and Z636×R7 vs R7, respectively, which were mainly enriched in carbon metabolism and amino acid biosynthesis pathways. Transcriptome data and qRT-PCR were combined to analyze the expression levels of genes related to storage polymers. It was found that the expression levels of some starch synthase genes, namely AGP-L, AGP-S and GBSSI in Z636×R7 were higher than in R7 and among the 17 DEGs related to storage proteins, the expression levels of 14 genes in R7 were lower than those in Z636 and Z636×R7. According to the classification analysis of all differential metabolites, most belonged to carboxylic acids and derivatives, and fatty acyls were enriched in the biosynthesis of unsaturated fatty acids, niacin and nicotinamide metabolism, one-carbon pool by folate, etc. CONCLUSION: After allopolyploidization, the expression of genes related to starch synthesis was down-regulated in Z636×R7, and the process of starch synthesis was inhibited, resulting in delayed starch accumulation and prolongation of the seed development process. Therefore, at the same development time point, the starch accumulation of Z636×R7 lagged behind that of Z636. In this study, the expression of the GSe2 gene in Z636×R7 was higher than that of the two parents, which was beneficial to protein synthesis, and increased the protein content. These results eventually led to changes in the synthesis of seed reserve polymers. The current study provided a basis for a greater in-depth understanding of the mechanism of wheat allopolyploid formation and its stable preservation, and also promoted the effective exploitation of high-value alleles.

Response mechanism of carbon metabolism of Pinus massoniana to gradient high temperature and drought stress.

BACKGROUND: The carbon metabolism pathway is of paramount importance for the growth and development of plants, exerting a pivotal regulatory role in stress responses. The exacerbation of drought impacts on the plant carbon cycle due to global warming necessitates comprehensive investigation into the response mechanisms of Masson Pine (Pinus massoniana Lamb.), an exemplary pioneer drought-tolerant tree, thereby establishing a foundation for predicting future forest ecosystem responses to climate change. RESULTS: The seedlings of Masson Pine were utilized as experimental materials in this study, and the transcriptome, metabolome, and photosynthesis were assessed under varying temperatures and drought intensities. The findings demonstrated that the impact of high temperature and drought on the photosynthetic rate and transpiration rate of Masson Pine seedlings was more pronounced compared to individual stressors. The analysis of transcriptome data revealed that the carbon metabolic pathways of Masson Pine seedlings were significantly influenced by high temperature and drought co-stress, with a particular impact on genes involved in starch and sucrose metabolism. The metabolome analysis revealed that only trehalose and Galactose 1-phosphate were specifically associated with the starch and sucrose metabolic pathways. Furthermore, the trehalose metabolic heat map was constructed by integrating metabolome and transcriptome data, revealing a significant increase in trehalose levels across all three comparison groups. Additionally, the PmTPS1, PmTPS5, and PmTPPD genes were identified as key regulatory genes governing trehalose accumulation. CONCLUSIONS: The combined effects of high temperature and drought on photosynthetic rate, transpiration rate, transcriptome, and metabolome were more pronounced than those induced by either high temperature or drought alone. Starch and sucrose metabolism emerged as the pivotal carbon metabolic pathways in response to high temperature and drought stress in Masson pine. Trehalose along with PmTPS1, PmTPS5, and PmTPPD genes played crucial roles as metabolites and key regulators within the starch and sucrose metabolism.

A novel starch-active lytic polysaccharide monooxygenase discovered with bioinformatics screening and its application in textile desizing.

BACKGROUND: Lytic polysaccharide monooxygenases (LPMOs) catalyzing the oxidative cleavage of different types of polysaccharides have potential to be used in various industries. However, AA13 family LPMOs which specifically catalyze starch substrates have relatively less members than AA9 and AA10 families to limit their application range. Amylase has been used in enzymatic desizing treatment of cotton fabric for semicentury which urgently need for new assistant enzymes to improve reaction efficiency and reduce cost so as to promote their application in the textile industry. RESULTS: A total of 380 unannotated new genes which probably encode AA13 family LPMOs were discovered by the Hidden Markov model scanning in this study. Ten of them have been successfully heterologous overexpressed. AlLPMO13 with the highest activity has been purified and determined its optimum pH and temperature as pH 5.0 and 50 °C. It also showed various oxidative activities on different substrates (modified corn starch > amylose > amylopectin > corn starch). The results of enzymatic textile desizing application showed that the best combination of amylase (5 g/L), AlLPMO13 (5 mg/L), and H2O2 (3 g/L) made the desizing level and the capillary effects increased by 3 grades and more than 20%, respectively, compared with the results treated by only amylase. CONCLUSION: The Hidden Markov model constructed basing on 34 AA13 family LPMOs was proved to be a valid bioinformatics tool for discovering novel starch-active LPMOs. The novel enzyme AlLPMO13 has strong development potential in the enzymatic textile industry both concerning on economy and on application effect.

Influence of maize genotypes and harvest stages on in-silo fermentation quality and nutritional value of corn silage during hot summer condition of the tropics.

The aim of the experiment was to evaluate the potential of promising summer maize genotypes and optimal stage of harvesting these genotypes for ensiling in terms of dry matter (DM), starch, and crude protein (CP) yields, silage fermentation quality, nutrients profile, total digestible nutrients, metabolizable energy (ME) content, Cornell Net Carbohydrate and Protein System (CNCPS) carbohydrate (CHO) subfractions composition, in vitro DM digestibility (DMD) and in situ starch degradation characteristics. Six maize genotypes were chosen for the study: DK9108 from Monsanto, P30Y87, P3939 from Pioneer, QPM-300 (quality protein maize) and W94 from the International Maize and Wheat Improvement Center (CIMMYT), and a local cultivar, Afgoii, from the Cereal Research Institute (Persabaq, KP). A total of 72 plots (8 m × 10 m) were blocked in three replicate fields, and within each field, each genotype was sown in four replicate plots according to a randomized complete block design. For the data analysis, the Proc-Mixed procedure of Statistical Analysis System with repeated measure analysis of variance was used. The DM yield was strongly influenced (P < 0.001) by maize genotypes, varying from 12.6 to 17.0 tons/ha. Except for total CHO and ammonia nitrogen (NH3-N), the contents of all measured chemical components varied (P < 0.001) among the genotypes. Further comparison revealed that, genotype P3939 had a higher (P < 0.05) content of CP (7.27 vs. 6.92%), starch (36.7 vs. 27.9%), DMD (65.4 vs. 60.0%), ME (2.51 vs. 2.30 Mcal/kg) and lactic acid (5.32 vs. 4.83%) and lowest content of NDF (37.3 vs. 43.1%), pH (3.7 vs. 4.10) compared to the local cultivar (Afgoii). Advancement of post-flowering maturity from 25 to 35% DM (23 to 41 days after flowering (DAF)) increased (P < 0.05) the DM yield (10.4 to 17.8 tons/ha), starch content (29.1 to 35.0%), DMD (65.3 to 67.3%) and ME (2.34 to 2.47 Mcal/kg), and decreased (P < 0.001) the contents of CP (7.42-6.73%), NDF (48.8-38.5%), pH (4.10 to 3.60), NH3-N (8.93-7.80%N) and effective degradability of starch (95.4 to 89.4). Results showed that for higher yields and silage nutritional and fermentation quality, maize crops should be harvested at whole crop DM content of 30-35% (34 to 41 DAF). It was further concluded that genotype P3939 is the most suitable summer maize genotype for silage production in terms of yields and silage nutritional and fermentation quality under the hot environmental conditions of the tropics.

Exogenous abscisic acid (ABA) improves the filling process of maize grains at different ear positions by promoting starch accumulation and regulating hormone levels under high planting density.

BACKGROUND: Higher planting densities typically cause a decline in grain weight, limiting the potential for high maize yield. Additionally, variations in grain filling occur at different positions within the maize ear. Abscisic acid (ABA) is important for grain filling and regulates grain weight. However, the effects of exogenous ABA on the filling process of maize grains at different ear positions under high planting density are poorly understood. In this study, two summer maize hybrids (DengHai605 (DH605) and ZhengDan958 (ZD958)) commonly grown in China were used to examine the effects of ABA application during the flowering stage on grain filling properties, starch accumulation, starch biosynthesis associated enzyme activities, and hormone levels of maize grain (including inferior grain (IG) and superior grain (SG)) under high planting density. RESULTS: Our results showed that exogenous ABA significantly increased maize yield, primarily owing to a higher grain weight resulting from an accelerated grain filling rate relative to the control. There was no significant difference in yield between DH605 and ZD958 in the control and ABA treatments. Moreover, applying ABA promoted starch accumulation by raising the activities of sucrose synthase, ADP-glucose pyrophosphorylase, granule-bound starch synthases, soluble starch synthase, and starch branching enzyme in grains. It also increased the levels of zeatin riboside, indole-3-acetic acid, and ABA and decreased the level of gibberellin in grains, resulting in more efficient grain filling. Notably, IG exhibited a less efficient filling process compared to SG, probably due to lower starch biosynthesis associated enzyme activities and an imbalance in hormone contents. Nevertheless, IG displayed greater sensitivity to exogenous ABA than SG, suggesting that appropriate cultural measures to improve IG filling may be a viable strategy to further increase maize yield. CONCLUSIONS: According to our results, spraying exogenous ABA could effectively improve grain filling properties, accelerate starch accumulation by increasing relevant enzyme activities, and regulate hormone levels in grains, resulting in higher grain weight and yield of maize under high planting density. Our findings offer more evidence for using exogenous hormones to improve maize yield under high planting density.