Sequential breakdown of the Cf-9 leaf mould resistance locus in tomato by Fulvia fulva.

Leaf mould, caused by Fulvia fulva, is a devastating disease of tomato plants. In many commercial tomato cultivars, resistance to this disease is governed by the Cf-9 locus, which encodes five paralogous receptor-like proteins. Two of these proteins confer resistance: Cf-9C recognises the previously identified F. fulva effector Avr9 and provides resistance during all plant growth stages, while Cf-9B recognises the yet-unidentified F. fulva effector Avr9B and provides mature plant resistance only. In recent years, F. fulva strains have emerged that can overcome the Cf-9 locus, with Cf-9C circumvented through Avr9 deletion. To understand how Cf-9B is circumvented, we set out to identify Avr9B. Comparative genomics, transient expression assays and gene complementation experiments were used to identify Avr9B, while gene sequencing was used to assess Avr9B allelic variation across a world-wide strain collection. A strict correlation between Avr9 deletion and resistance-breaking mutations in Avr9B was observed in strains recently collected from Cf-9 cultivars, whereas Avr9 deletion but no mutations in Avr9B were observed in older strains. This research showcases how F. fulva has evolved to sequentially break down the Cf-9 locus and stresses the urgent need for commercial tomato cultivars that carry novel, stacked resistance genes active against this pathogen.

SlCYP94B18 and SlCYP94B19 monooxygenases for the catabolic turnover of jasmonates in tomato leaves.

(3R,7S)-Jasmonoyl-L-isoleucine (JA-Ile) is a plant hormone that regulates plant defense responses and other physiological functions. The mechanism of attenuation of JA-Ile signaling in the plant body is essential because prolonged JA-Ile signaling can be detrimental to plant survival. In Arabidopsis thaliana, the cytochrome P450 monooxygenases, CYP94B1/B3/C1, inactivate JA-Ile by converting it into 12-hydroxy-jasmonoyl-L-isoleucine (12-OH-JA-Ile), and CYP94C1 converts 12-OH-JA-Ile into 12-carboxy-jasmonoyl-L-isoleucine (12-COOH-JA-Ile). In the present study, we aimed to identify the cytochrome P450 monooxygenases involved in the catabolic pathway of JA-Ile in tomato leaves. Based on a gene expression screening of SlCYP94 subfamily monooxygenases using qPCR and the time-course of JA-Ile catabolism, we identified SlCYP94B18 and SlCYP94B19 expressed in tomato leaves as candidate monooxygenases catalyzing the two-step catabolism of JA-Ile. An in vitro enzymatic assay using a yeast expression system revealed that these enzymes efficiently converted JA-Ile to 12-OH-JA-Ile, and then to 12-COOH-JA-Ile. SlCYP94B18 and SlCYP94B19 also catalyzed the oxidative catabolism of several JA-amino acid conjugates (JA-AAs), JA-Leu and JA-Val, in tomatoes. These results suggest that SlCYP94B18 and SlCYP94B19 plays a role in the two-step oxidation of JA-AAs, suggesting their broad involvement in regulating jasmonate signaling in tomatoes. Our results contribute to a deeper understanding of jasmonate signaling in tomatoes and may help to improve tomato cultivation and quality.

Plant growth-promoting rhizobacteria Pseudomonas aeruginosa HG28-5 improves salt tolerance by regulating Na+/K+ homeostasis and ABA signaling pathway in tomato.

Salinity stress badly restricts the growth, yield and quality of vegetable crops. Plant growth-promoting rhizobacteria (PGPR) is a friendly and effective mean to enhance plant growth and salt tolerance. However, information on the regulatory mechanism of PGPR on vegetable crops in response to salt stress is still incomplete. Here, we screened a novel salt-tolerant PGPR strain Pseudomonas aeruginosa HG28-5 by evaluating the tomatoes growth performance, chlorophyll fluorescence index, and relative electrolyte leakage (REL) under normal and salinity conditions. Results showed that HG28-5 colonization improved seedling growth parameters by increasing the plant height (23.7%), stem diameter (14.6%), fresh and dry weight in the shoot (60.3%, 91.1%) and root (70.1%, 92.5%), compared to salt-stressed plants without colonization. Likewise, HG28-5 increased levels of maximum photochemical efficiency of PSII (Fv/Fm) (99.3%), the antioxidant enzyme activities as superoxide dismutase (SOD, 85.5%), peroxidase (POD, 35.2%), catalase (CAT, 20.6%), and reduced the REL (48.2%), MDA content (41.3%) and ROS accumulation in leaves of WT tomatoes under salt stress in comparison with the plants treated with NaCl alone. Importantly, Na+ content of HG28-5 colonized salt-stressed WT plants were decreased by15.5% in the leaves and 26.6% in the roots in the corresponding non-colonized salt-stressed plants, which may be attributed to the higher K+ concentration and SOS1, SOS2, HKT1;2, NHX1 transcript levels in leaves of colonized plants under saline condition. Interestingly, increased abscisic acid (ABA) content and upregulation of ABA pathway genes (ABA synthesis-related genes NCED1, NCED2, NCED4, NECD6 and signal genes ABF4, ABI5, and AREB) were observed in HG28-5 inoculated salt-stressed WT plants. ABA-deficient mutant (not) with NCED1 deficiency abolishes the effect of HG28-5 on alleviating salt stress in tomato, as exhibited by the substantial rise of REL and ROS accumulation and sharp drop of Fv/Fm in the leaves of not mutant plants. Notably, HG28-5 colonization enhances tomatoes fruit yield by 54.9% and 52.4% under normal and saline water irrigation, respectively. Overall, our study shows that HG28-5 colonization can significantly enhance salt tolerance and improved fruit yield by a variety of plant protection mechanism, including reducing oxidative stress, regulating plant growth, Na+/K+ homeostasis and ABA signaling pathways in tomato. The findings not only deepen our understanding of PGPR regulation plant growth and salt tolerance but also allow us to apply HG28-5 as a microbial fertilizer for agricultural production in high-salinity areas.

Phyllosphere microbial associations improve plant reproductive success.

The above-ground (phyllosphere) plant microbiome is increasingly recognized as an important component of plant health. We hypothesized that phyllosphere bacterial recruitment may be disrupted in a greenhouse setting, and that adding a bacterial amendment would therefore benefit the health and growth of host plants. Using a newly developed synthetic phyllosphere bacterial microbiome for tomato (Solanum lycopersicum), we tested this hypothesis across multiple trials by manipulating microbial inoculation of leaves and measuring subsequent plant growth and reproductive success, comparing results from plants grown in both greenhouse and field settings. We confirmed that greenhouse-grown plants have a relatively depauperate phyllosphere bacterial microbiome, which both makes them an ideal system for testing the impact of phyllosphere communities on plant health and important targets for microbial amendments as we move towards increased agricultural sustainability. We find that the addition of the synthetic microbial community early in greenhouse growth leads to an increase in fruit production in this setting, implicating the phyllosphere microbiome as a key component of plant fitness and emphasizing the role that these bacterial microbiomes likely play in the ecology and evolution of plant communities.

Microbially produced fertilizer provides rhizobacteria to hydroponic tomato roots by forming beneficial biofilms.

Hydroponic cultivation of Solanum lycopersicum (tomato) is important, and high tomato production depends on the use of nitrogen and phosphate fertilizers. We had developed a microbial fertilizer (MF), which is mainly composed of nitrate. To investigate the effect of MF on plant growth, hydroponic tomato was grown with MF or commercial inorganic fertilizer (IF), and the microbiomes of the rhizosphere and the liquid phase were analyzed by confocal microscopy and high-throughput sequencing. Plant biomass and biofilm formation were increased by growth in MF compared to IF. The microbial community structures of tomato roots and hydroponic water differed between the two conditions, and three operational taxonomic units (OTUs) dominated in plants grown with MF. The three OTUs were related to Rudaea spp., Chitinophaga spp., and Stenotrophobacter terrae, which are reported to be disease-suppressive epiphytic or endophytic microbes of plant roots. Because these three OTUs also predominated in the MF itself, they were likely provided to the rhizosphere or endophytic environments of tomato roots via hydroponic water. KEY POINTS: • Microbial fertilizer for hydroponic growth enhanced biofilm formation on tomato root. • Microbial fertilizer contains tomato-root epiphytic or endophytic microbes. • Microbial fertilizer provided beneficial microbes to the rhizosphere and endophytic environments of tomato roots via hydroponic water.

Variation in ripe fruit volatiles across the tomato clade: An evolutionary framework for studying fruit scent diversity in a crop wild relative.

PREMISE: The scents of volatile organic compounds (VOCs) are an important component of ripe fleshy fruit attractiveness, yet their variation across closely related wild species is poorly understood. Phylogenetic patterns in these compounds and their biosynthetic pathways offer insight into the evolutionary drivers of fruit diversity, including whether scent can communicate an honest signal of nutrient content to animal dispersers. We assessed ripe fruit VOC content across the tomato clade (Solanum sect. Lycopersicon), with implications for crop improvement since these compounds are key components of tomato flavor. METHODS: We analyzed ripe fruit volatiles from 13 species of wild tomato grown in a common garden. Interspecific variations in 66 compounds and their biosynthetic pathways were assessed in 32 accessions, and an accession-level phylogeny was constructed to account for relatedness. RESULTS: Wild tomato species can be differentiated by their VOCs, with Solanum pennellii notably distinct. Phylogenetic conservatism exists to a limited extent. Major cladewide patterns corresponded to divergence of the five brightly colored-fruited species from the nine green-fruited species, particularly for nitrogen-containing compounds (higher in colored-fruited) and esters (higher in green-fruited), the latter appearing to signal a sugar reward. CONCLUSIONS: We established a framework for fruit scent evolution studies in a crop wild relative system, showing that each species in the tomato clade has a unique VOC profile. Differences between color groups align with fruit syndromes that could be driven by selection from frugivores. The evolution of colored fruits was accompanied by changes in biosynthetic pathways for esters and nitrogen-containing compounds, volatiles important to tomato flavor.

Herbivore-induced Ca2+ signals trigger a jasmonate burst by activating ERF16-mediated expression in tomato.

Herbivory severely affects plant growth, posing a threat to crop production. Calcium ion (Ca2+ ) signaling and accumulation of jasmonates (JAs) are activated in plant response to herbivore attack, leading to the expression of defense pathways. However, little is known about how the Ca2+ signal modulates JA biosynthesis. We used diverse techniques, including CRISPR/Cas9, UPLC-MS/MS and molecular biology methods to explore the role of ETHYLENE RESPONSE FACTOR 16 in Ca2+ signal-triggered JA burst during herbivore defense in tomato. Here we show that simulated herbivory induces GLUTAMATE RECEPTOR LIKE3.3/3.5 (GLR3.3/3.5)-dependent increases in electrical activity, Ca2+ influx and increases the abundance of CALMODULIN2 (CaM2) and ERF16 transcripts in tomato. The interaction between CaM2 and ERF16 promotes JA biosynthesis by enhancing the transcriptional activity of ERF16, which increases the activation of ERF16 expression and causes expression of LIPOXYGENASE D (LOXD), AOC and 12-OXO-PHYTODIENOIC ACID REDUCTASE 3 (OPR3), the key genes in JA biosynthesis. Mutation of CaM2 results in decreased JA accumulation, together with the expression of JA biosynthesis-related genes, leading to reduced resistance to the cotton bollworm Helicoverpa armigera. These findings reveal a molecular mechanism underpinning the Ca2+ signal-initiated systemic JA burst and emphasize the pivotal role of Ca2+ signal/ERF16 crosstalk in herbivore defense.

The basic helix-loop-helix transcription factors MYC1 and MYC2 have a dual role in the regulation of constitutive and stress-inducible specialized metabolism in tomato.

Plants produce specialized metabolites to protect themselves from biotic enemies. Members of the Solanaceae family accumulate phenylpropanoid-polyamine conjugates (PPCs) in response to attackers while also maintaining a chemical barrier of steroidal glycoalkaloids (SGAs). Across the plant kingdom, biosynthesis of such defense compounds is promoted by jasmonate signaling in which clade IIIe basic helix-loop-helix (bHLH) transcription factors play a central role. By characterizing hairy root mutants obtained through Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-CRISPR associated protein 9 (CRISPR-Cas9) genome editing, we show that the tomato clade IIIe bHLH transcription factors, MYC1 and MYC2, redundantly control jasmonate-inducible PPC and SGA production, and are also essential for constitutive SGA biosynthesis. Double myc1 myc2 loss-of-function tomato hairy roots displayed suppressed constitutive expression of SGA biosynthesis genes, and severely reduced levels of the main tomato SGAs α-tomatine and dehydrotomatine. In contrast, basal expression of genes involved in PPC biosynthesis was not affected. CRISPR-Cas9(VQR) genome editing of a specific cis-regulatory element, targeted by MYC1/2, in the promoter of a SGA precursor biosynthesis gene led to decreased constitutive expression of this gene, but did not affect its jasmonate inducibility. Our results demonstrate that clade IIIe bHLH transcriptional regulators have evolved under the control of distinct regulatory cues to specifically steer constitutive and stress-inducible specialized metabolism.

Functional roles of ALMT-type anion channels in malate-induced stomatal closure in tomato and Arabidopsis.

Guard-cell-type aluminium-activated malate transporters (ALMTs) are involved in stomatal closure by exporting anions from guard cells. However, their physiological and electrophysiological functions are yet to be explored. Here, we analysed the physiological and electrophysiological properties of the ALMT channels in Arabidopsis and tomato (Solanum lycopersicum). SlALMT11 was specifically expressed in tomato guard cells. External malate-induced stomatal closure was impaired in ALMT-suppressed lines of tomato and Arabidopsis, although abscisic acid did not influence the stomatal response in SlALMT11-knock-down tomato lines. Electrophysiological analyses in Xenopus oocytes showed that SlALMT11 and AtALMT12/QUAC1 exhibited characteristic bell-shaped current-voltage patterns dependent on extracellular malate, fumarate, and citrate. Both ALMTs could transport malate, fumarate, and succinate, but not citrate, suggesting that the guard-cell-type ALMTs are dicarboxylic anion channels activated by extracellular organic acids. The truncation of acidic amino acids, Asp or Glu, from the C-terminal end of SlALMT11 or AtALMT12/QUAC1 led to the disappearance of the bell-shaped current-voltage patterns. Our findings establish that malate-activated stomatal closure is mediated by guard-cell-type ALMT channels that require an acidic amino acid in the C-terminus as a candidate voltage sensor in both tomato and Arabidopsis.

Low Salicylic Acid Level Improves Pollen Development Under Long-Term Mild Heat Conditions in Tomato.

Exposure to high temperatures leads to failure in pollen development, which may have significant implications for food security with ongoing climate change. We hypothesized that the stress response-associated hormone salicylic acid (SA) affects pollen tolerance to long-term mild heat (LTMH) (≥14 days exposure to day-/nighttime temperature of 30-34/24-28°C, depending on the genotype), either positively, by inducing acclimation, or negatively, by reducing investment in reproductive development. Here, we investigated these hypotheses assessing the pollen thermotolerance of a 35S:nahG tomato line, which has low SA levels. We found that reducing the SA level resulted in increased pollen viability of plants grown in LTMH and further characterized this line by transcriptome, carbohydrate, and hormone analyses. Low expression of JAZ genes in 35S:nahG and LTMH hypersensitivity of low-jasmonic acid (JA) genotypes together suggest that the increased pollen thermotolerance in the low-SA line involves enhanced JA signal in developing anthers in LTMH. These findings have potential application in the development of more thermotolerant crops.

Effects of Light Quality on Colonization of Tomato Roots by AMF and Implications for Growth and Defense.

Beneficial soil microbes can enhance plant growth and defense, but the extent to which this occurs depends on the availability of resources, such as water and nutrients. However, relatively little is known about the role of light quality, which is altered during shading, resulting a low red: far-red ratio (R:FR) of light. We examined how low R:FR light influences arbuscular mycorrhizal fungus (AMF)-mediated changes in plant growth and defense using Solanum lycopersicum (tomato) and the insect herbivore Chrysodeixis chalcites. We also examined effects on third trophic level interactions with the parasitoid Cotesia marginiventris. Under low R:FR light, non-mycorrhizal plants activated the shade avoidance syndrome (SAS), resulting in enhanced biomass production. However, mycorrhizal inoculation decreased stem elongation in shaded plants, thus counteracting the plant's SAS response to shading. Unexpectedly, activation of SAS under low R:FR light did not increase plant susceptibility to the herbivore in either non-mycorrhizal or mycorrhizal plants. AMF did not significantly affect survival or growth of caterpillars and parasitoids but suppressed herbivore-induced expression of jasmonic acid-signaled defenses genes under low R:FR light. These results highlight the context-dependency of AMF effects on plant growth and defense and the potentially adverse effects of AMF under shading.

Reproductive water supply is prioritized during drought in tomato.

Reproductive success largely defines the fitness of plant species. Understanding how heat and drought affect plant reproduction is thus key to predicting future plant fitness under rising global temperatures. Recent work suggests reproductive tissues are highly vulnerable to water stress in perennial plants where reproductive sacrifice could preserve plant survival. However, most crop species are annuals where such a strategy would theoretically reduce fitness. We examined the reproductive strategy of tomato (Solanum lycopersicum var. Rheinlands Ruhm) to determine whether water supply to fruits is prioritized above vegetative tissues during drought. Using optical methods, we mapped xylem cavitation and tissue shrinkage in vegetative and reproductive organs during dehydration to determine the priority of water flow under acute water stress. Stems and peduncles of tomato showed significantly greater xylem cavitation resistance than leaves. This maintenance of intact water supply enabled tomato fruit to continue to expand during acute water stress, utilizing xylem water made available by tissue collapse and early cavitation of leaves. Here, tomato plants prioritize water supply to reproductive tissues, maintaining fruit development under drought conditions. These results emphasize the critical role of water transport in shaping life history and suggest a broad relevance of hydraulic prioritization in plant ecology.

Phytochrome interacting factor 3 regulates pollen mitotic division through auxin signalling and sugar metabolism pathways in tomato.

The development of viable pollen determines male fertility, and is crucial for reproduction in flowering plants. Phytochrome interacting factor 3 (PIF3) acts as a central regulator of plant growth and development, but its relationship with pollen development has not been determined. Through genetic, histological and transcriptomic analyses, we identified an essential role for SlPIF3 in regulating tomato (Solanum lycopersicum) pollen development. Knocking out SlPIF3 using clustered regularly interspaced short palindromic repeats/CRISPR-associated protein 9 resulted in pollen mitosis I arrest, and a failure to form viable pollen. We further demonstrated that both glutamate synthase 1 (SlGLT1) and cell wall invertase 9 (SlCWIN9), involved in auxin and sugar homeostasis, respectively, colocalised with SlPIF3 in the anthers and were directly regulated by SlPIF3. Knockout of either SlGLT1 or SlCWIN9 phenocopied the pollen phenotype of SlPIF3 knockout (Slpif3) lines. Slpif3 fertility was partially restored by exogenous auxin indole-3-acetic acid in a dose-dependent manner. This study reveals a mechanism by which SlPIF3 regulates pollen development and highlights a new strategy for creating hormone-regulated genic male sterile lines for tomato hybrid seed production.

Regulation of sugar metabolism genes in the nitrogen-dependent susceptibility of tomato stems to Botrytis cinerea.

BACKGROUND AND AIMS: The main soluble sugars are important components of plant defence against pathogens, but the underlying mechanisms are unclear. Upon infection by Botrytis cinerea, the activation of several sugar transporters, from both plant and fungus, illustrates the struggle for carbon resources. In sink tissues, the metabolic use of the sugars mobilized in the synthesis of defence compounds or antifungal barriers is not fully understood. METHODS: In this study, the nitrogen-dependent variation of tomato stem susceptibility to B. cinerea was used to examine, before and throughout the course of infection, the transcriptional activity of enzymes involved in sugar metabolism. Under different nitrate nutrition regimes, the expression of genes that encode the enzymes of sugar metabolism (invertases, sucrose synthases, hexokinases, fructokinases and phosphofructokinases) was determined and sugar contents were measured before inoculation and in asymptomatic tissues surrounding the lesions after inoculation. KEY RESULTS: At high nitrogen availability, decreased susceptibility was associated with the overexpression of several genes 2 d after inoculation: sucrose synthases Sl-SUS1 and Sl-SUS3, cell wall invertases Sl-LIN5 to Sl-LIN9 and some fructokinase and phosphofructokinase genes. By contrast, increased susceptibility corresponded to the early repression of several genes that encode cell wall invertase and sucrose synthase. The course of sugar contents was coherent with gene expression. CONCLUSIONS: The activation of specific genes that encode sucrose synthase is required for enhanced defence. Since the overexpression of fructokinase is also associated with reduced susceptibility, it can be hypothesized that supplementary sucrose cleavage by sucrose synthases is dedicated to the production of cell wall components from UDP-glucose, or to the additional implication of fructose in the synthesis of antimicrobial compounds, or both.

BRASSINAZOLE RESISTANT 1 Mediates Brassinosteroid-Induced Calvin Cycle to Promote Photosynthesis in Tomato.

Calvin cycle is a sequence of enzymatic reactions that assimilate atmospheric CO2 in photosynthesis. Multiple components are known to participate in the induction or suppression of the Calvin cycle but the mechanism of its regulation by phytohormones is still unclear. Brassinosteroids (BRs) are steroid phytohormones that promote photosynthesis and crop yields. In this study, we study the role of BRs in regulating Calvin cycle genes to further understand the regulation of the Calvin cycle by phytohormones in tomatoes. BRs and their signal effector BRASSINAZOLE RESISTANT 1 (BZR1) can enhance the Calvin cycle activity and improve the photosynthetic ability. BRs increased the accumulation of dephosphorylated form of BZR1 by 94% and induced an 88-126% increase in the transcription of key genes in Calvin cycle FBA1, RCA1, FBP5, and PGK1. BZR1 activated the transcription of these Calvin cycle genes by directly binding to their promoters. Moreover, silencing these Calvin cycle genes impaired 24-epibrassinolide (EBR)-induced enhancement of photosynthetic rate, the quantum efficiency of PSII, and V c,max and J max . Taken together, these results strongly suggest that BRs regulate the Calvin cycle in a BZR1-dependent manner in tomatoes. BRs that mediate coordinated regulation of photosynthetic genes are potential targets for increasing crop yields.

Chitosan primes plant defence mechanisms against Botrytis cinerea, including expression of Avr9/Cf-9 rapidly elicited genes.

Current crop protection strategies against the fungal pathogen Botrytis cinerea rely on a combination of conventional fungicides and host genetic resistance. However, due to pathogen evolution and legislation in the use of fungicides, these strategies are not sufficient to protect plants against this pathogen. Defence elicitors can stimulate plant defence mechanisms through a phenomenon known as defence priming. Priming results in a faster and/or stronger expression of resistance upon pathogen recognition by the host. This work aims to study defence priming by a commercial formulation of the elicitor chitosan. Treatments with chitosan result in induced resistance (IR) in solanaceous and brassicaceous plants. In tomato plants, enhanced resistance has been linked with priming of callose deposition and accumulation of the plant hormone jasmonic acid (JA). Large-scale transcriptomic analysis revealed that chitosan primes gene expression at early time-points after infection. In addition, two novel tomato genes with a characteristic priming profile were identified, Avr9/Cf-9 rapidly elicited protein 75 (ACRE75) and 180 (ACRE180). Transient and stable over-expression of ACRE75, ACRE180 and their Nicotiana benthamiana homologs, revealed that they are positive regulators of plant resistance against B. cinerea. This provides valuable information in the search for strategies to protect Solanaceae plants against B. cinerea.

Far-red radiation stimulates dry mass partitioning to fruits by increasing fruit sink strength in tomato.

Far-red (FR) light promotes fruit growth by increasing dry mass partitioning to fruits, but the mechanism behind this is unknown. We hypothesise that it is due to an increased fruit sink strength as FR radiation enhances sugar transportation and metabolism. Tomato plants were grown with or without 50-80 µmol m-2  s-1 of FR radiation added to a common background 150-170 µmol m-2  s-1 red + blue light-emitting diode lighting. Potential fruit growth, achieved by pruning each truss to one remaining fruit, was measured to quantify fruit sink strength. Model simulation was conducted to test whether the measured fruit sink strength quantitatively explained the FR effect on dry mass partitioning. Starch, sucrose, fructose and glucose content were measured. Expression levels of key genes involved in sugar transportation and metabolism were determined. FR radiation increased fruit sink strength by 38%, which, in model simulation, led to an increased dry mass partitioned to fruits that quantitatively agreed very well with measured partitioning. FR radiation increased fruit sugar concentration and upregulated the expression of genes associated with both sugar transportation and metabolism. This is the first study to demonstrate that FR radiation stimulates dry mass partitioning to fruits mainly by increasing fruit sink strength via simultaneous upregulation of sugar transportation and metabolism.

Genetic Control of Glandular Trichome Development.

Plant glandular trichomes are epidermal secretory structures producing various specialized metabolites. These metabolites are involved in plant adaptation to its environment and many of them have remarkable properties exploited by fragrance, flavor, and pharmaceutical industries. The identification of genes controlling glandular trichome development is of high interest to understand how plants produce specialized metabolites. Our knowledge about this developmental process is still limited, but genes controlling glandular trichome initiation and morphogenesis have recently been identified. In particular, R2R3-MYB and HD-ZIP IV transcription factors appear to play essential roles in glandular trichome initiation in Artemisia annua and tomato. In this review, we focus on the results obtained in these two species and we propose genetic regulation models integrating these data.

Leaf shape is a predictor of fruit quality and cultivar performance in tomato.

Commercial tomato (Solanum lycopersicum) is one of the most widely grown vegetable crops worldwide. Heirloom tomatoes retain extensive genetic diversity and a considerable range of fruit quality and leaf morphological traits. Here the role of leaf morphology was investigated for its impact on fruit quality. Heirloom cultivars were grown in field conditions, and BRIX by yield (BY) and other traits were measured over a 14-wk period. The complex relationships among these morphological and physiological traits were evaluated using partial least-squares path modeling, and a consensus model was developed. Photosynthesis contributed strongly to vegetative biomass and sugar content of fruits but had a negative impact on yield. Conversely leaf shape, specifically rounder leaves, had a strong positive impact on both fruit sugar content and yield. Cultivars such as Stupice and Glacier, with very round leaves, had the highest performance in both fruit sugar and yield. Our model accurately predicted BY for two commercial cultivars using leaf shape data as input. This study revealed the importance of leaf shape to fruit quality in tomato, with rounder leaves having significantly improved fruit quality. This correlation was maintained across a range of diverse genetic backgrounds and shows the importance of leaf morphology in tomato crop improvement.

Roles of RIN and ethylene in tomato fruit ripening and ripening-associated traits.

RIPENING INHIBITOR (RIN)-deficient fruits generated by CRISPR/Cas9 initiated partial ripening at a similar time to wild-type (WT) fruits but only 10% WT concentrations of carotenoids and ethylene (ET) were synthesized. RIN-deficient fruit never ripened completely, even when supplied with exogenous ET. The low amount of endogenous ET that they did produce was sufficient to enable ripening initiation and this could be suppressed by the ET perception inhibitor 1-MCP. The reduced ET production by RIN-deficient tomatoes was due to an inability to induce autocatalytic system-2 ET synthesis, a characteristic feature of climacteric ripening. Production of volatiles and transcripts of key volatile biosynthetic genes also were greatly reduced in the absence of RIN. By contrast, the initial extent and rates of softening in the absence of RIN were similar to WT fruits, although detailed analysis showed that the expression of some cell wall-modifying enzymes was delayed and others increased in the absence of RIN. These results support a model where RIN and ET, via ERFs, are required for full expression of ripening genes. Ethylene initiates ripening of mature green fruit, upregulates RIN expression and other changes, including system-2 ET production. RIN, ET and other factors are required for completion of the full fruit-ripening programme.