Ethylene is a key plant hormone controlling the ripening of climacteric fruits, and several transcription factors acting as important regulators of fruit ripening have been identified in tomato (Solanum lycopersicum), a model for climacteric fruits. The vast majority of these transcription factors are transcriptional activators, however, and the associated transcriptional regulatory mechanisms of most regulators are unclear. Here, we report on a tomato transcriptional repressor (termed SlMYB70) that negatively regulates fruit ripening by directly modulating ethylene biosynthesis. As an EAR motif-containing MYB transcription factor-encoding gene, SlMYB70 displayed a ripening-associated expression pattern and was responsive to ethylene. RNA interference (RNAi)-mediated repression of SlMYB70 accelerated fruit ripening, but overexpression of SlMYB70 delayed fruit ripening. Ethylene production was noticeably increased and decreased in SlMYB70-RNAi and SlMYB70-overexpressing lines, respectively, compared with wild-type tomatoes. SlMYB70 was proven to be a transcriptional repressor, dependent on the EAR repression motif, and to repress the transcription of two ethylene biosynthesis genes in fruit ripening, namely SlACS2 and SlACO3. The promoters of SlACS2 and SlACO3 are directly bound by SlMYB70, which was verified using a combination of yeast one-hybrid chromatin immunoprecipitation quantitative polymerase chain reaction and electrophoretic mobility shift assays. These results suggest that SlMYB70 negatively regulates fruit ripening via the direct transcriptional repression of ethylene biosynthesis genes, which provides insights into the ethylene-mediated key regulatory hierarchy in climacteric fruit ripening, and also highlights different types of transcriptional regulation of fruit ripening.
Leaf morphogenetic activity determines its shape diversity. However, our knowledge to the regulatory mechanism in maintaining leaf morphogenetic capacity is still limited. In tomato, gibberellin (GA) negatively regulates leaf complexity by shortening the morphogenetic window. We here reported a tomato BRI1-EMS-SUPPRESSOR 1 (BES1) transcription factor, SlBES1.8, that promoted the simplification of leaf pattern in a similar manner as GA functions. OE-SlBES1.8 plants exhibited reduced sensibility to exogenous GA3 treatment whereas showed increased sensibility to the application of GA biosynthesis inhibitor, PAC. In line with the phenotypic observation, the endogenous bioactive GA contents were increased in OE-SlBES1.8 lines, which certainly promoted the degradation of the GA signaling negative regulator, SlDELLA. Moreover, transcriptomic analysis uncovered a set of overlapping genomic targets of SlBES1.8 and GA, and most of them were regulated in the same way. Expression studies showed the repression of SlBES1.8 to the transcriptions of two GA deactivated genes, SlGA2ox2 and SlGA2ox6, and one GA receptor, SlGID1b-1. Further experiments confirmed the direct regulation of SlBES1.8 to their promoters. On the other hand, SlDELLA physically interacted with SlBES1.8 and further inhibited its transcriptional regulation activity by abolishing SlBES1.8-DNA binding. Conclusively, by mediating GA deactivation and signaling, SlBES1.8 greatly influenced tomato leaf morphogenesis.
Maize is an essential source of nutrition for humans and animals, which is rich in various metabolites and determine its quality. Different maize varieties show significant differences in metabolite content. Two kinds of waxy maize parental materials, S181 and 49B, created by the Chongqing Academy of Agricultural Sciences, are widely grown in China. S181 shows higher starch and sugar contents than 49B. This study generated metabolic profiles to assess the differences between the two varieties. A total of 674 metabolites that were significantly differentially expressed between the two varieties were identified by gas chromatography and untargeted metabolomics technology. These metabolites were associated with 21 categories, including antioxidant metabolites. Moreover, 6415 differentially expressed genes (DEGs) were identified by RNA-seq. Interestingly, these DEGs comprised starch and sugar synthesis pathway genes and 72 different transcription factor families. Of these, 6 families which were reported to play an essential role in plant antioxidant action accounted for 39.2% of the transcription factor families. Using the KEGG classification, the DEGs were mainly involved in amino acid biosynthesis, glycolysis/glucose metabolism, and the synthetic and metabolic pathways of antioxidant active substances. Furthermore, the correlation analysis of transcriptome and metabonomics identified five key transcription factors(ZmbHLH172, ZmNAC44, ZmNAC-like18, ZmS1FA2, ZmERF172, one ubiquitin ligase gene(ZmE2 5A) and one sucrose synthase gene(ZmSS1). They likely contribute to the quality traits of waxy corn through involvement in the metabolic regulatory network of antioxidant substances. Thus, our results provide new insights into maize quality-related antioxidant metabolite networks and have potential applications for waxy corn breeding.
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