Biology subjects

Sreelakshmi, Y.

Publications and source records attributed to Sreelakshmi, Y..

17 recordsLinked to original sources

bioRxiv2026

Root-Suppressed Phenotype of Tomato Rs Mutant is Seemingly Related to Expression of Root-Meristem-Specific Sulfotransferases

Root development and growth are governed by a complex interplay between a plants genetic makeup and its ambient environment. In this study, we characterised a radiation-induced root-suppressed (Rs) mutant mapped on chromosome 4 of tomato. Rs seedlings had a dwarf stature, and mature plants exhibited abnormalities in their leaves, flowers, and fruits. The partial rescue of seedling root elongation by H2S donors or L-cysteine hinted that its root defect is linked to disrupted sulfur metabolism. The metabolite profiling of organs revealed altered homeostasis, analogous to that of plants subjected to sulfur starvation. Whole-genome sequencing revealed that the Rs genome was replete with genetic lesions; therefore, the pleiotropic morphological abnormalities likely emanate from mutations in other genes, including those related to sulfur. Among S-related genes, two sulfotransferase genes (Solyc04g028380 and Solyc04g028390) localised on chromosome 4 showed mutations in their promoters. The expression of both sulfotransferases is confined to the root meristem, suggesting a causal connection with the suppression of root growth. These sulfotransferases belonged to a distinct subset exclusively expressed in the root meristem and were distinct from the tyrosine sulfotransferase involved in the sulfation of root growth factors. Our study suggests that a sulfur-related module, other than tyrosine sulfotransferase, may regulate root development.

plant biology↗

bioRxiv2025

Loss-of-Function RUP-Variants Influence Ubiquitin-Proteasome System and Enhance Carotenoid and Folate Levels in Tomato

REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) negatively regulates UV- B signalling, yet its broader physiological roles in crop plants remain largely unexplored. We compared two tomato accessions bearing truncated RUP proteins--rup-1 and rup-2 (rup- variants)--with the cultivar Arka Vikas (AV), which harbours the native RUP protein. Seedlings of rup-variants exhibited enhanced tolerance to supplemental UV-B light. Red ripe (RR) fruits of rup-variants showed significantly elevated carotenoid and folate levels compared to AV. Introgression of rup-variants into AV confirmed that the increased carotenoid accumulation is genetically linked to RUP truncation. Metabolomic profiling of rup-variants revealed a substantial shift in primary metabolic homeostasis, particularly at the breaker stage, marked by a pronounced reduction in sugars and amino acids. Proteomic analyses of rup- variants across ripening stages identified that a significant proportion of differentially expressed proteins belonged to chaperones and ubiquitin-proteasome system (UPS). Upregulation of four key enzymes in the carotenoid biosynthesis pathway likely contributed to increased lycopene content in rup-variants. Elevated folate levels in rup-variants were associated with the upregulation of folate biosynthesis and C1 metabolism enzymes. Despite widespread metabolic reprogramming in rup-variants, hormonal regulatory pathways remained largely unaltered. Our results suggest that RUP modulates metabolic pathways during fruit ripening, and its loss triggers metabolic reprogramming associated with elevated folate/carotenoid levels.

plant biology↗

bioRxiv2023

A tomato ethylene-insensitive mutant displays altered growth and higher β-carotene levels in fruit

The mutants insensitive to ethylene are helpful in deciphering the role of ethylene in plant development. We isolated an ethylene-insensitive tomato (Solanum lycopersicum) mutant by screening for acetylene-resistant (atr-1) seedlings. The atr-1 mutant displayed resistance to kinetin, suggesting attenuation of the ethylene sensing response. atr-1 also exhibited resistance to ABA- and glucose-mediated inhibition of seed germination. Unlike the Never- ripe (Nr) mutant, atr-1 seedlings were resistant to glucose, indicating ethylene sensing in atr-1 is located in a component distinct from Nr. Metabolically, atr-1 seedlings had lower levels of amino acids but higher levels of several phytohormones, including ABA. atr-1 plants grew faster and produced more flowers, leading to a higher fruit set. However, the atr- 1 fruits took a longer duration to reach the red-ripe (RR) stage. The ripened atr-1 fruits had higher {beta}-carotene levels, retained high {beta}-carotene and lycopene levels post-RR stage. The metabolome profiles of post-RR stage atr-1 fruits revealed increased levels of sugars. The atr-1 had a P279L mutation in the GAF domain of the ETR4, a key ethylene receptor regulating tomato ripening. Our study highlights that novel alleles in ethylene receptors may aid in enhancing the nutritional quality of tomato.

plant biology↗

bioRxiv2023

Establishing Ac/Ds Starter Lines for Large-Scale Transposon-Tagged Mutagenesis in Tomato

Tomato (Solanum lycopersicum), a model system for ripening of fleshy fruits, has [~]40,000 genes predicted by in silico homology-based annotation. However, functional validation is lacking for most annotated tomato genes. Among the strategies for functional annotations, transposon-tagged mutagenesis is the most powerful approach. Transposon- tagged genes can be functionally validated by phenotyping and activation tagging. However, the lack of a robust in planta transformation system precludes large-scale transposon- mutagenesis of tomato. To overcome this limitation, we developed two sets of starter lines in tomato, each carrying maize transposon element (Ds) and transposase (Ac), respectively. The Ds and Ac lines were crossed to allow the Ac-mediated transposition of the Ds in the F1 generation. In the F2 generation, the location of excised Ds at new sites in the tomato genome was monitored. The Ds transposition was interspersed on different chromosomes of the tomato, indicating unlinked transposition of the Ds. The analysis of DNA sequences flanking Ds showed random integration of Ds in intergenic, genes, and the promoter region of the genome. Our study paves the way for the generation of large-scale transposon-tagged tomato lines using Ac/Ds starter lines and provides a potential tool for the functional validation of genes in tomato. Short summaryWe developed two sets of starter lines in tomato, carrying maize transposon element (Ds) and transposase (Ac), to enable large-scale transposon-mutagenesis, facilitating functional validation of tomato genes and for generating an insertional mutant resource in tomato.

plant biology↗

bioRxiv2023

Introgression of a dominant phototropin1 mutant superenhances carotenoids and boosts flavor-related volatiles in genome-edited tomato RIN mutants

The tomato (Solanum lycopersicum) ripening inhibitor (rin) mutation is known to completely repress fruit ripening. The heterozygous (RIN/rin) fruits have extended shelf life, ripen normally, but have poor taste and flavour. Even the CRISPR/Cas9-generated rin alleles have these undesirable attributes associated with the rin mutation. To address this, we used genome editing to generate newer alleles of RIN (rinCR) by targeting the K domain, which is essential for the oligomerization of MADS-box transcription factors. Unlike previously reported CRISPR alleles, the rinCRalleles displayed delayed onset of ripening, suggesting that the mutated K domain represses the onset of ripening. The rinCR fruits had extended shelf life and accumulated carotenoids at an intermediate level between rin and wild-type parent. Besides, the metabolites and hormonal levels in rinCR fruits were more akin to rin. To overcome the negative attributes of rin, we crossed the rinCR alleles with Nps1, which enhances carotenoid levels in tomato fruits. Nps1 harbours a dominant-negative mutation in the plant photoreceptor phototropin1. The resulting Nps1/rinCR hybrids had extended shelf life and 4.4-7.1-fold higher carotenoid levels than the wild-type parent. The Nps1/rinCR fruits had higher auxin and reduced ABA levels, which are reportedly linked with slower ripening. The metabolome of Nps1/rinCRfruits revealed higher sucrose, malate, and volatiles associated with tomato taste and flavour. Notably, the boosted volatile levels in Nps1/rinCR were only observed in fruits bearing the homozygous Nps1 (Nps1/Nps1) mutation. Our findings suggest that the Nps1 introgression into tomato ripening mutants provides a promising strategy for developing tomato cultivars with extended shelf life, improved taste, and flavour.

plant biology↗

bioRxiv2022

Reduced γ-glutamyl hydrolase activity likely contributes to high folate levels in Periyakulam-1 tomato

Tomato cultivars show wide variation in nutraceutical folate in ripe fruits, yet the loci regulating folate levels in fruits remain unexplored. To decipher regulatory points, we compared two contrasting tomato cultivars: Periyakulam-1 (PKM-1) with high folate and Arka Vikas (AV) with low folate. The progression of ripening in PKM-1 was nearly similar to AV but had substantially lower ethylene emission. In parallel, the levels of phytohormones salicylic acid, ABA, and jasmonic acid were substantially lower than AV. The fruits of PKM-1 were also metabolically distinct from AV, with upregulation of several amino acids. Consistent with higher {degrees}Brix levels, the red ripe fruits also showed upregulation of sugars and sugar-derived metabolites. In parallel with higher folate, PKM-1 fruits also had higher carotenoid levels, especially lycopene and {beta}-carotene. Transcript levels of genes encoding folate biosynthesis did not show a perceptible difference in relative expression. The proteome analysis showed upregulation of carotenoid sequestration and folate metabolism-related proteins in PKM-1. The deglutamylation pathway mediated by {gamma}-glutamyl hydrolase (GGH) was substantially reduced in PKM-1 at the red-ripe stage. The red-ripe fruits had reduced transcript levels of GGHs and lower GGH activity than AV. Conversely, the percent polyglutamylation of folate was much higher in PKM-1. Our analysis indicates the regulation of GGH activity as a potential target to elevate folate levels in tomato fruits.

plant biology↗

bioRxiv2022

Whole-Genome Profiling of Ethyl Methanesulfonate Mutagenesis in Tomato

The induced mutations accelerate crop improvement by providing novel disease resistance and yield alleles. However, the alleles with no perceptible phenotype but having an altered function remain hidden in mutagenized plants. The whole-genome sequencing (WGS) of mutagenized individuals uncovers the complete spectrum of mutations in the genome. We sequenced 132 doubly ethyl methanesulfonate (EMS)-mutagenized lines of tomato and detected ca. 41 million SNPs and 5.5 million short-INDELs. We found a very high average density of mutations 1/3.05 Kb compared to other species. About 97% of the genome had mutations, including the genes, promoters, UTRs, and introns. More than 1/3rd of genes in the mutagenized population had one or more deleterious mutations predicted by SIFT. Nearly 1/4th of deleterious genes mapped on tomato metabolic pathways modulating multiple pathway steps. Contrary to the reported GC>AT transition bias for EMS, we found EMS also produced nearly equal AT>GC transitions. Comparing mutation frequency among synonymous codons revealed that the most preferred codon is least mutagenic towards EMS. The reduction in carotenoids in {zeta}-carotene isomerase mutant fruits and chloroplasts relocation loss in phototropin1 mutant validated the mutation discovery pipeline. Our study makes a large repertoire of mutations accessible to genetic studies and the breeding of tomato.

plant biology↗

bioRxiv2021

Seeing the unseen: A trifoliate (MYB117) mutant allele fortifies folate and carotenoids in tomato fruits

Micronutrient deficiency also termed hidden hunger affects a large segment of the human population, particularly in developing and underdeveloped nations. Tomato the second most consumed vegetable crop in the world after potato can serve as a sustainable source to alleviate micronutrient deficiency. In tomato, the mutations in the R2R3-MYB117 transcription factor elicit trifoliate leaves and initiate axillary meristems; however, its effect on fruit metabolome remains unexplored. The fruits of a new trifoliate (tf) allele (tf-5) were firmer, had higher {degrees}Brix, folate, and carotenoids. The transcriptome, proteome, and metabolome profiling of tf-5 reflected a broad-spectrum change in homeostasis. The tf-5 allele enhanced the fruit firmness by suppressing cell wall softening-related proteins. The tf-5 fruit displayed a substantial increase in aminome, particularly {gamma}-aminobutyric acid, with a parallel reduction in aminoacyl t-RNA synthases. The increased lipoxygenases proteins and transcripts seemingly elevated jasmonic acid. In addition, increased abscisic acid hydrolases transcripts coupled with reduced precursor supply lowered abscisic acid. The upregulation of carotenoids was mediated by modulation of methylerythreitol and plastoquinone pathways along with an increase in carotenoids isomerization proteins. The upregulation of folate in tf-5 was connoted by the increase in precursor p-aminobenzoic acid and transcripts of several folate biosynthesis pathway genes. The reduction in pterin-6-carboxylate and {gamma}-glutamyl hydrolase activity indicated that the diminished folate degradation also enriched folate levels. Our study delineates that introgression of the tf-5 can be used for the {gamma}-aminobutyric acid, carotenoids, and folate fortification of tomato. One-sentence summaryA tomato trifoliate allele encoding a truncated MYB117 transcription factor alters cellular homeostasis and fortifies {gamma}-aminobutyric acid, folate, and carotenoids in tomato fruits.

plant biology↗

bioRxiv2021

Chemical inhibition of lycopene β-cyclases unmask operation of phytoene synthase 2 in ripening tomato fruits

In ripening tomato fruits, the leaf-specific carotenoids biosynthesis mediated by phytoene synthase 2 (PSY2) is replaced by a fruit-specific pathway by the expression of two chromoplast-specific genes: phytoene synthase 1 (PSY1) and lycopene-{beta}-cyclase (CYCB). Though both PSY1 and PSY2 genes express in tomato fruits, the functional role of PSY2 is not known. To decipher whether PSY2-mediated carotenogenesis operates in ripening fruits, we blocked the in vivo activity of lycopene-{beta}-cyclases in fruits of several carotenoids and ripening mutants by CPTA (2-(4-Chlorophenylthio)triethylamine hydrochloride), an inhibitor of lycopene-{beta}-cyclases. The CPTA-treatment induced accumulation of lycopene in leaves, immature-green and ripening fruits. Even, in psy1 mutants V7 and r that are deficient in fruit-specific carotenoid biosynthesis, CPTA triggered lycopene accumulation but lowered the abscisic acid level. Differing from fruit-specific carotenogenesis, CPTA-treated V7 and r mutant fruits accumulated lycopene but not phytoene and phytofluene. The lack of phytoene and phytofluene accumulation was reminiscent of PSY2-mediated leaf-like carotenogenesis, where phytoene and phytofluene accumulation is never seen. The lycopene accumulation was associated with the partial transformation of chloroplasts to chromoplasts bearing thread-like crystalline structures. Our study uncovers the operation of a parallel carotenogenesis pathway mediated by PSY2 that provides precursors for abscisic acid biosynthesis in ripening tomato fruits. Significance statementIt is believed that in ripening tomato fruits phytoene synthase 2 that drives carotenoid biosynthesis in leaves is redundant. Contrary to this, we show that in phytoene synthase 1 mutant fruit that is bereft of lycopene, the chemical inhibition of lycopene {beta}-cyclases triggers lycopene accumulation. Our results uncover that phytoene synthase 2 remains functional in ripening fruits and provides precursors for abscisic acid formation in fruits.

plant biology↗

bioRxiv2021

Tomato roots sense horizontal/vertical mechanical impedance and divergently modulate root/shoot metabolome

Plant roots encounter coarse environs right after emergence from the seeds. Little is known about metabolic changes enabling roots to overcome the soil impedance. Tomato seedlings grown vertically or horizontally, at increasing hardness, exhibited lateral roots proliferation, shorter hypocotyls, and primary roots. In primary root tips, hardness-elicited loss of amyloplasts staining; induced ROS and NO accumulation. The levels of IBA, zeatin, jasmonates, and salicylic acids markedly differed in roots and shoots exposed to increasing hardness. Hardness lowered IAA and elevated ABA levels, while increased ethylene emission was confined to horizontally-impeded seedlings. The trajectories of metabolomic shifts distinctly differed between vertically/horizontally-impeded roots/shoots. In horizontal roots, amino acids were the major affected group, while in vertical roots, sugars were the major group. Commonly affected metabolites in roots and shoots, trehalose, dopamine, caffeoylquinic acid, and suberic acid, hallmarked the signature for hardness. Increasing hardness lowered SnRK1a expression in roots/shoots implying regulation of metabolic homeostasis by the SnRK1 signalling module. Our data suggest that though hardness is a common denominator, roots sense the horizontal/vertical orientation and correspondingly modulate metabolite profiles. Significance statementWe show that the tomato roots sense the magnitude of hardness as well as the horizontal and vertical orientation. The hardness divergently modulates the phytohormone and metabolite levels in roots and shoots. The trajectory of the metabolic shift in vertically-grown seedling distinctly differs from horizontally-grown seedlings. ABA and trehalose were the hallmark of hardness stress and may influence metabolic alteration via the SNRK signalling pathway.

plant biology↗

bioRxiv2020

The new kid on the block: A dominant-negative mutation of phototropin1 enhances carotenoid content in tomato fruits

Phototropins, the UVA-blue light photoreceptors, endow plants to detect the direction of light and optimize photosynthesis by regulating chloroplasts positioning and stomatal gas exchange. Little is known about their functions in other developmental responses. A tomato Non-phototropic seedling1 (Nps1) mutant, bearing an Arg495His substitution in the vicinity of LOV2 domain in phototropin1, dominant-negatively blocks phot1 and phot2 responses. The fruits of Nps1 mutant were enriched in carotenoids, particularly lycopene, than its parent, Ailsa Craig. Contrarily, CRISPR/CAS9-edited loss of function phototropin1 mutants displayed subdued carotenoids than the parent. The enrichment of carotenoids in Nps1 fruits is genetically linked with the mutation and exerted in a dominant-negative fashion. Nps1 also altered volatile profiles with high levels of lycopene-derived 6-methyl 5-hepten2-one. The transcript levels of several MEP and carotenogenesis pathways genes were upregulated in Nps1. Nps1 fruits showed altered hormonal profiles with subdued ethylene emission and reduced respiration. Proteome profiles showed a causal link between higher carotenogenesis and increased levels of protein protection machinery, which may stabilize proteins contributing to MEP and carotenogenesis pathways. Given the enhancement of carotenoid content by Nps1 in a dominant-negative fashion, it offers a potential tool for high lycopene-bearing hybrid tomatoes. One-sentence summaryA dominant-negative phototropin1 mutation enhances carotenoid levels, alters metabolite homeostasis, and protein quality control machinery in tomato fruits.

plant biology↗

bioRxiv2020

Mutations in Tomato 1-Aminocyclopropane Carboxylic Acid Synthase2 Uncover Its Role in Development beside System II Responses

The role of ethylene in plant development is mostly inferred from its exogenous application. The usage of the mutants affecting ethylene biosynthesis proffers a better alternative to decipher its role. In tomato, 1-aminocyclopropane carboxylic acid synthase2 (ACS2) is a key enzyme regulating ripening-specific ethylene biosynthesis. We characterized two contrasting acs2 mutants; acs2-1 overproduces ethylene, has higher ACS activity, and increased protein levels, while acs2-2 is an ethylene under-producer, displays lower ACS activity, and protein levels than wild type. Consistent with high/low ethylene emission, the mutants show opposite phenotypes, physiological responses, and metabolomic profiles than the wild type. The acs2-1 showed early seed germination, faster leaf senescence, and accelerated fruit ripening. Conversely, acs2-2 had delayed seed germination, slower leaf senescence, and prolonged fruit ripening. The phytohormone profiles of mutants were mostly opposite in the leaves and fruits. The faster/slower senescence of acs2-1/acs2-2 leaves correlated with the endogenous ethylene/zeatin ratio. The genetic analysis showed that the metabolite profiles of respective mutants co-segregated with the homozygous mutant progeny. Our results uncover that besides ripening, ACS2 participates in vegetative and reproductive development of tomato. The distinct influence of ethylene on phytohormone profiles indicates intertwining of ethylene action with other phytohormones in regulating plant development.

plant biology↗

bioRxiv2020

Reanalysis of Genome Sequences of tomato accessions and its wild relatives: Development of tomato genomic variation (TGV) database integrating SNPs and INDELs polymorphisms

MotivationFacilitated by technological advances and expeditious decrease in the sequencing costs, whole-genome sequencing (WGS) is increasingly implemented to uncover variations in cultivars/accessions of many crop plants. In tomato (Solanum lycopersicum), the availability of the genome sequence, followed by the resequencing of tomato cultivars and its wild relatives, has provided a prodigious resource for the improvement of traits. A high-quality genome resequencing of 84 tomato accessions and wild relatives generated a dataset that can be used as a resource to identify agronomically important alleles across the genome. Converting this dataset into a searchable database, including information about the influence of SNPs on protein function, provides valuable information about the genetic variations. The database will assist in searching for functional variants of a gene for introgression into tomato cultivars. ResultsA recent release of better-quality tomato genome reference assembly SL3.0, and new annotation ITAG3.2 of SL3.0, dropped 3,857 genes, added 4,900 novel genes, and updated 20,766 genes. Using the above version, we remapped the data from the tomato lines resequenced under the "100 Tomato Genome ReSequencing Project" on new tomato genome assembly SL3.0 and made an online searchable Tomato Genomic Variations (TGV) database. The TGV contains information about SNPs and InDels and expands it by functional annotation of variants with new ITAG3.2 using SIFT4G software. This database with search function assists in inferring the influence of SNPs on the function of a target gene. This database can be used for selecting SNPs, which can be potentially deployed for improving tomato traits. Availability and ImplementationTGV is freely available at http://psd.uohyd.ac.in/tgv. Contactrameshwar.sharma@gmail.com

bioinformatics↗

bioRxiv2019

Enhanced polar auxin transport in tomato polycotyledon mutant seems to be related to glutathione levels

Glutathione-dependent root growth in Arabidopsis is linked to polar auxin transport (PAT). Arabidopsis mutants with reduced glutathione (GSH) levels also show reduced PAT. To gain an insight into the relationship between PAT and GSH level, we analysed tomato polycotyledon mutant, pct1-2, which has enhanced PAT. Microarray analysis of gene expression in pct1-2 mutant revealed underexpression of several genes related to glutamate and glutathione metabolism. In consonance with microarray analysis, enzymatic as well as in-vivo assay revealed higher glutathione level in the early phase of pct1-2 seedling growth than WT. The inhibition of auxin transport by 2,3,5-triiodobenzoic acid (TIBA) reduced both GSH level and PIN1 expression in pct1-2 root tips. The reduction of in vivo GSH accumulation in pct1-2 root tips by buthionine sulfoximine (BSO) stimulated elongation of the short root of pct1-2 mutant akin to TIBA. The rescue of short root phenotype of pct1-2 mutant was restricted to TIBA and BSO. The other auxin transport inhibitors 1-N-naphthylphthalamic acid (NPA), 2-[4-(diethylamino)-2-hydroxybenzoyl] benzoic acid (BUM), 3-chloro-4-hydroxyphenylacetic acid (CHPAA), brefeldin and gravacin inhibited root elongation in both WT and pct1-2 mutant. Our results indicate a relationship between PAT and GSH level in tomato akin to Arabidopsis. Our work also highlights that TIBA rescues short root phenotype of the pct1-2 mutant by acting on a PAT component distinct from the site of action of other PAT inhibitors.

plant biology↗

bioRxiv2018

N-1-naphthylphthalamic acid stimulates tomato hypocotyl elongation, elevates ethylene levels and alters metabolic homeostasis

One sentence summaryN-1-naphthylphthalamic acid (NPA) treatment stimulates tomato hypocotyl elongation likely by elevating ethylene emission and lowering indole-3-butyric acid levels in the seedlings.\n\nAbstractIn higher plants, phytohormone indole-3-acetic acid is characteristically transported from the apex towards the base of the plant, termed as polar auxin transport (PAT). Among the inhibitors blocking PAT, N-1-naphthylphthalamic acid (NPA) that targets ABCB transporters is most commonly used. NPA-treated light-grown Arabidopsis seedlings show severe inhibition of hypocotyl and root elongation. In light-grown tomato seedlings, NPA inhibited root growth, but contrary to Arabidopsis stimulated hypocotyl elongation. The NPA-stimulation of hypocotyl elongation was milder in blue, red, and far-red light-grown seedlings. The NPA-treatment stimulated emission of ethylene from the seedlings. The scrubbing of ethylene by mercuric perchlorate reduced NPA-stimulated hypocotyl elongation. NPA action on hypocotyl elongation was antagonized by 1-methylcyclopropene, an inhibitor of ethylene action. NPA-treated seedlings had reduced levels of indole-3-butyric acid and higher levels of zeatin in the shoots. NPA did not alter indole-3-acetic levels in shoots. The analysis of metabolic networks indicated that NPA-treatment induced moderate shifts in the networks compared to exogenous ethylene that induced a drastic shift in metabolic networks. Our results indicate that in addition to ethylene, NPA-stimulated hypocotyl elongation in tomato may also involve zeatin and indole-3-butyric acid. Our results indicate that NPA-mediated physiological responses may vary in a species-specific fashion.

plant biology↗

bioRxiv2017

NAC-NOR mutations in tomato Penjar accessions attenuate multiple metabolic processes and prolong the fruit shelf life

Several Penjar accessions of tomato (Solanum lycopersicum), widely grown in the Mediterranean region, exhibit prolonged shelf life, and harbor alcobaca mutation with valine-106-aspartic acid substitution in the NAC-NOR protein. To uncover the metabolic basis underlying the prolonged shelf life, we compared four Penjar accessions to Ailsa Craig (AC). Three accessions bore alcobaca mutation, whereas fourth was a novel NAC-NOR allele with only six amino acids in the encoded protein. The cuticle composition among Penjars varied widely during the progression of fruit ripening. All Penjars exhibited delayed ripening, prolonged on-vine and off-vine shelf life, low ethylene emission and carotenoid levels albeit with accession-specific differences. Metabolic profiling revealed shifts in Krebs cycle intermediates, amino acids, and {beta}-aminobutyric acid levels indicating the attenuation of respiration in Penjars during post-harvest storage. The prolonged shelf life of Penjar fruits was associated with a concerted downregulation of a number of cell-wall modifying genes and cell-wall-related metabolites. The accumulation of higher ABA and sucrose levels at the onset of senescence in Penjar fruits likely contribute to reduced water loss. Our analyses reveal that in addition to specialized cuticle composition, the attenuation of various metabolic processes by NAC-NOR mutation likely prolongs the shelf life of Penjar fruits.\n\nHighlightThe prolonged shelf life of tomato Penjar accessions bearing mutations in NAC-NOR transcription factor appears to be regulated by a combined effect of attenuation of respiration, altered cuticle composition, enhanced ABA and sucrose levels in fruits and downregulation of cell wall modification

plant biology↗

bioRxiv2017

MutS-Homolog2 Silencing Generates Tetraploid Meiocytes In Tomato (Solanum lycopersicum)

MSH2 is the core protein of MutS-homolog family involved in recognition and repair of the errors in the DNA. While other members of MutS-homolog family reportedly regulate mitochondrial stability, meiosis, and fertility, MSH2 is believed to participate mainly in mismatch repair. The search for polymorphism in MSH2 sequence in tomato accessions revealed both synonymous and nonsynonymous SNPs; however, SIFT algorithm predicted that none of the SNPs influenced MSH2 protein function. The silencing of MSH2 gene expression by RNAi led to phenotypic abnormalities in highly-silenced lines, particularly in the stamens with highly reduced pollen formation. MSH2 silencing exacerbated formation of UV-B induced thymine dimers and blocked light-induced repair of the dimers. The MSH2 silencing also affected the progression of male meiosis to a varying degree with either halt of meiosis at zygotene stage or formation of diploid tetrads. The immunostaining of male meiocytes with centromere localized CENPC (Centromere protein C) protein antibody showed the presence of 48 univalent along with 24 bivalent chromosomes suggesting abnormal tetraploid meiosis. The mitotic cells of root tips of silenced lines showed diploid nuclei but lacked intervening cell plates leading to cells with syncytial nuclei. Thus we speculate that tetraploid pollen mother cells may have arisen due to the fusion of syncytial nuclei before the onset of meiosis. It is likely that in addition to Mismatch repair (MMR), MSH2 may have an additional role in regulating ploidy stability.

plant biology↗