Firmness is one of the most important factors that affect postharvest properties of tomato fruit. However, the regulatory mechanism underlying firmness formation in tomato fruit is poorly understood. Here, we report a novel role of SlBES1, a transcriptional factor (TF) mediating brassinosteroid (BR) signaling, in tomato fruit softening. We first found that SlBES1 promotes fruit softening during tomato fruit ripening and postharvest storage. RNA-seq analysis suggested that PMEU1, which encodes a pectin de-methylesterification protein, might participate in SlBES1-mediated fruit softening. Biochemical and immunofluorescence assays in SlBES1 transgenic fruits indicated that SlBES1 inhibited PMEU1-related pectin de-methylesterification. Further molecular and genetic evidence verified that SlBES1 directly binds to the E-box in the promoter of PMEU1 to repress its expression, leading to the softening of the tomato fruits. Loss-of-function SlBES1 mutant generated by CRISPR/cas9 showed firmer fruits and longer shelf life during postharvest storage without the color, size and nutritional quality alteration. Collectively, our results indicated the potential of manipulating SlBES1 to regulate fruit firmness via transcriptional inhibition of PMEU1 without negative consequence on visual and nutrition quality.

中文翻译：

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油菜素类固醇信号转导成分SlBES1通过转录抑制PMEU1促进番茄果实软化

硬度是影响番茄果实采后特性的最重要因素之一。然而，对番茄果实坚硬形成的调控机制了解甚少。在这里，我们报告的SlBES1，介导油菜素类固醇（BR）信号传导的转录因子（TF）在番茄果实软化中的新型作用。我们首先发现，SlBES1在番茄果实成熟和收获后储存过程中促进果实软化。RNA-seq分析表明，编码果胶脱甲基酯化蛋白的PMEU1可能参与SlBES1介导的果实软化。SlBES1转基因水果的生化和免疫荧光分析表明，SlBES1抑制了PMEU1相关果胶脱甲基酯化。进一步的分子和遗传证据证实，SlBES1直接与PMEU1启动子中的E-box结合以抑制其表达，从而导致番茄果实变软。由CRISPR / cas9产生的功能丧失的SlBES1突变体在收获后的贮藏过程中显示出更牢固的果实和更长的货架寿命，而没有颜色，大小和营养品质的改变。总的来说，我们的结果表明操纵SlBES1可以通过转录抑制PMEU1来调节果实硬度，而对视觉和营养质量没有负面影响。