A molecular framework for lc controlled locule development of the floral meristem in tomato.

Malformed tomato fruit with multiple locules is a common physiological disorder that significantly affects the quality of tomatoes. Research has shown that the occurrence of malformed fruit in tomatoes is closely linked to the number of locules, and two key QTLs, lc and fas, are involved in controlling this trait. It has been observed that lc has a relatively weaker effect on increasing locule number, which is associated with two SNPs in the CArG repressor element downstream of the SlWUS. However, the precise molecular mechanism underlying lc is not yet fully understood. In this study, we investigated the role of lc in tomato locule development. We found that the number of floral organs and fruit locules significantly increased in tomato lc knockout mutants. Additionally, these mutants showed higher expression levels of the SlWUS during carpel formation. Through cDNA library construction and yeast one-hybrid screening, we identified the MADS-box transcription factor SlSEP3, which was found to bind to lc. Furthermore, we observed an increase in floral organs and fruit locules similar to the lc CR plant on SlSEP3 silencing plants. However, it should be noted that the lc site is located after the 3' untranslated region (UTR) of SlWUS in the tomato genome. As a result, SlSEP3 may not be able to exert regulatory functions on the promoter of the gene like other transcription factors. In the yeast two-hybrid assay, we found that several histone deacetylases (SlHDA1, SlHDA3, SlHDA4, SlHDA5, SlHDA6, SlHDA7, and SlHDA8) can interact with SlSEP3. This indicated that SlSEP3 can recruit these proteins to repress nucleosome relaxation, thereby inhibiting SlWUS transcription and affecting the number of locules in tomato fruit. Therefore, our findings reveal a new mechanism for lc playing a significant role in the genetic pathway regulating tomato locule development.

Effects of Low Temperature on Pedicel Abscission and Auxin Synthesis Key Genes of Tomato.

Cold stress usually causes the abscission of floral organs and a decline in fruit setting rate, seriously reducing tomato yield. Auxin is one of the key hormones that affects the abscission of plant floral organs; the YUCCA (YUC) family is a key gene in the auxin biosynthesis pathway, but there are few research reports on the abscission of tomato flower organs. This experiment found that, under low temperature stress, the expression of auxin synthesis genes increased in stamens but decreased in pistils. Low temperature treatment decreased pollen vigor and pollen germination rate. Low night temperature reduced the tomato fruit setting rate and led to parthenocarpy, and the treatment effect was most obvious in the early stage of tomato pollen development. The abscission rate of tomato pTRV-Slfzy3 and pTRV-Slfzy5 silenced plants was higher than that of the control, which is the key auxin synthesis gene affecting the abscission rate. The expression of Solyc07g043580 was down-regulated after low night temperature treatment. Solyc07g043580 encodes the bHLH-type transcription factor SlPIF4. It has been reported that PIF4 regulates the expression of auxin synthesis and synthesis genes, and is a key protein in the interaction between low temperature stress and light in regulating plant development.

PGR5/PGRL1 and NDH Mediate Far-Red Light-Induced Photoprotection in Response to Chilling Stress in Tomato.

Plants experience low ambient temperature and low red to far-red ratios (L-R/FR) of light due to vegetative shading and longer twilight durations in cool seasons. Low temperature induce photoinhibition through inactivation of the photosynthetic apparatus, however, the role of light quality on photoprotection during cold stress remains poorly understood. Here, we report that L-R/FR significantly prevents the overreduction of the entire intersystem electron transfer chain and the limitation of photosystem I (PSI) acceptor side, eventually alleviating the cold-induced photoinhibition. During cold stress, L-R/FR activated cyclic electron flow (CEF), enhanced protonation of PSII subunit S (PsbS) and de-epoxidation state of the xanthophyll cycle, and promoted energy-dependent quenching (qE) component of non-photochemical quenching (NPQ), enzyme activity of Foyer-Halliwell-Asada cycle and D1 proteins accumulation. However, L-R/FR -induced photoprotection pathways were compromised in tomato PROTON GRADIENT REGULATION5 (PGR5) and PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE1A (PGRL1A) co-silenced plants and NADH DEHYDROGENASE-LIKE COMPLEX M (NDHM) -silenced plants during cold stress. Our results demonstrate that both PGR5/PGRL1- and NDH-dependent CEF mediate L-R/FR -induced cold tolerance by enhancing the thermal dissipation and the repair of photodamaged PSII, thereby mitigating the overreduction of electron carriers and the accumulation of reactive oxygen species. The study indicates that there is an anterograde link between photoreception and photoprotection in tomato plants during cold stress.

Tomato YABBY2b controls plant height through regulating indole-3-acetic acid-amido synthetase (GH3.8) expression.

Dwarfing is a desirable agronomic trait in cultivation management. Dwarf plants are lodging-resistant, compact, and perform well under high-density planting. The use of dwarf genetic resources is one approach to improve crop yield. YABBY2b in tomato (Solanum lycopersicum) encodes a transcription factor that regulates plant height. In this study, we created YABBY2b knockout mutant lines, and the resulting yabby2b plants exhibited reduced height and smaller flowers and fruits. The RNA-seq analysis showed that 17 genes responding to gibberellin and auxin were differentially expressed. We hypothesized that indole-3-acetic acid-amido synthetase GH3.8 (GH3.8) played a crucial role in the resulting yabby2b dwarf phenotype. Further analysis showed that YABBY2b suppresses GH3.8 gene expression by directly binding to its promoter, and that this contributes to auxin-mediated repression of GH3.8. Moreover, the silencing of GH3.8 led to increased plant height. Combined, our data suggest that YABBY2b may positively regulate plant height in tomato by inhibiting the expression of growth suppressor GH3.8.

Low Overnight Temperature-Induced Gibberellin Accumulation Increases Locule Number in Tomato.

The number of locules in tomato affects fruit size, shape, and the incidence of malformation. Low temperature increases locule number and the incidences of malformation in tomato plants. In this study, three flower bud developmental stages (pre-flower bud differentiation, sepal and petal primordium formation, and carpel primordium formation) under different night temperatures (10, 15, and 20 °C) were used to analyze the reason behind locule number change using an RNA sequencing (RNA-seq) approach, Quantitative real-time PCR (qRT-PCR), and ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS). The results showed that the "plant hormone signal transduction", "starch and sucrose metabolism", and "diterpenoid biosynthesis" categories were remarkably activated during flower bud differentiation. Transcripts of gibberellin (GA)-related genes and endogenous levels of GAs were analyzed, and it was discovered that SlGA2ox genes were significantly downregulated and bioactive GA1 and GA4 accumulated at lower overnight temperature. Exogenous application of bioactive GA1, GA4, and PAC (paclobutrazol) showed that GA1 and GA4 increased the locule number, while PAC decreased the locule number. Taken together, our results suggest that lower overnight temperature reduced the expression of SlGA2ox genes, leading to GA1 and GA4 accumulation, thereby increasing locule number in tomato.