Trihelix transcription factor SlGT31 regulates fruit ripening mediated by ethylene in tomato

MeGT2.6 increases cellulose synthesis and active gibberellin content to promote cell enlargement in cassava

Cassava, a pivotal tropical crop, exhibits rapid growth and possesses a substantial biomass. Its stem is rich in cellulose and serves as a crucial carbohydrate storage organ. The height and strength of stems restrict the mechanised operation and propagation of cassava. In this study, the triple helix transcription factor MeGT2.6 was identified through yeast one-hybrid assay using MeCesA1pro as bait, which is critical for cellulose synthesis. Over-expression and loss-of-function lines were generated, and results revealed that MeGT2.6 could promote a significant increase in the plant height, stem diameter, cell size and thickness of SCW of cassava plant. Specifically, MeGT2.6 upregulated the transcription activity of MeGA20ox1 and downregulated the expression level of MeGA2ox1, thereby enhancing the content of active GA3, resulting in a large cell size, high plant height and long stem diameter in cassava. Moreover, MeGT2.6 upregulated the transcription activity of MeCesA1, which promoted the synthesis of cellulose and hemicellulose and produced a thick secondary cell wall. Finally, MeGT2.6 could help supply additional substrates for the synthesis of cellulose and hemicellulose by upregulating the invertase genes (MeNINV1/6). Thus, MeGT2.6 was found to be a multiple regulator; it was involved in GA metabolism and sucrose decomposition and the synthesis of cellulose and hemicellulose.

SlbHLH22-Induced Hypertrophy Development Is Related to the Salt Stress Response of the GTgamma Gene in Tomatoes

Hypertrophy development induced by the overexpression of SlbHLH22 (also called SlUPA-like) was susceptible to Xanthomonas in tomatoes. Transcriptome and metabolome analyses were performed on the hypertrophy leaves of a SlbHLH22-overexpressed line (OE) and wild type (WT) to investigate the molecular mechanism. Metabolome analysis revealed that six key metabolites were over-accumulated in the OE, including Acetylserine/O-Acetyl-L-serine, Glucono-1,5-lactone, Gluconate, 2-Oxoglutarate, and Loganate, implying that the OE plants increased salt or oxidant resistance under normal growth conditions. The RNA-seq analysis showed the changed expressions of downstream genes involved in high-energy consumption, photosynthesis, and transcription regulation in OE lines, and we hypothesized that these biological processes were related to the GTgamma subfamily of trihelix factors. The RT-PCR results showed that the expressions of the GTgamma genes in tomatoes, i.e., SlGT-7 and SlGT-36, were suppressed in the hypertrophy development. The expression of the GTgamma gene was downregulated by salinity, indicating a coordinated role of GTgamma in hypertrophy development and salt stress. Further research showed that both SlGT-7 and SlGT-36 were highly expressed in leaves and could be significantly induced by abscisic acid (ABA). The GTgamma protein had a putative phosphorylation site at S96. These results suggested GTgamma's role in hypertrophy development by increasing the salt resistance.

Trihelix transcription factor SlGT31 regulates fruit ripening mediated by ethylene in tomato

Trihelix proteins are plant-specific transcription factors that are classified as GT factors due to their binding specificity for GT elements, and they play crucial roles in development and stress responses. However, their involvement in fruit ripening and transcriptional regulatory mechanisms remains largely unclear. In this study, we cloned SlGT31, encoding a trihelix protein in tomato (Solanum lycopersicum), and determined that its relative expression was significantly induced by the application of exogenous ethylene whereas it was repressed by the ethylene-inhibitor 1-methylcyclopropene. Suppression of SlGT31 expression resulted in delayed fruit ripening, decreased accumulation of total carotenoids, and reduced ethylene content, together with inhibition of expression of genes related to ethylene and fruit ripening. Conversely, SlGT31-overexpression lines showed opposite results. Yeast one-hybrid and dual-luciferase assays indicated that SlGT31 can bind to the promoters of two key ethylene-biosynthesis genes, ACO1 and ACS4. Taken together, our results indicate that SlGT31 might act as a positive modulator during fruit ripening.