Brassinosteroids (BRs) play important roles in regulating plant reproductive processes. BR signaling or BR biosynthesis null mutants do not produce seeds under natural conditions, but the molecular mechanism underlying this infertility is poorly understood. In this study, we report that outer integument growth and embryo sac development were impaired in the ovules of the Arabidopsis thaliana BR receptor null mutant bri1‐116. Gene expression and RNA‐seq analyses showed that the expression of INNER NO OUTER (INO), an essential regulator of outer integument growth, was significantly reduced in the bri1‐116 mutant. Increased INO expression due to overexpression or increased transcriptional activity of BRASSINAZOLE‐RESISTANT 1 (BZR1) in the mutant alleviated the outer integument growth defect in bri1‐116 ovules, suggesting that BRs regulate outer integument growth partially via BZR1‐mediated transcriptional regulation of INO. Meanwhile, INO expression in bzr‐h, a null mutant for all BZR1 family genes, was barely detectable; and the outer integument of bzr‐h ovules had much more severe growth defects than those of the bri1‐116 mutant. Together, our findings establish a new role for BRs in regulating ovule development and suggest that BZR1 family transcription factors might regulate outer integument growth through both BRI1‐dependent and BRI1‐independent pathways.

中文翻译：

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油菜素类固醇部分地通过抗油菜籽抗性家族转录因子控制内在外来调节外胚珠被膜的生长。

油菜素类固醇（BRs）在调节植物生殖过程中起重要作用。BR信号转导或BR生物合成无效突变体在自然条件下不会产生种子，但对这种不孕症的分子机制了解甚少。在这项研究中，我们报告了拟南芥BR受体无效突变体bri1-116的胚珠中外珠被的生长和胚囊的发育受到损害。基因表达和RNA-seq分析表明，在bri-116突变体中，INNER NO OUTER（INO）（外皮生长的重要调节剂）的表达显着降低。INO增加突变体中BRASSINAZOLE-RESISTANT 1（BZR1）的过表达或转录活性增强引起的表达减轻了bri1-1116胚珠的外被膜生长缺陷，这表明BRs通过BZR1介导的INO转录调控部分调节了外被膜生长。同时，几乎检测不到INO在bzr-h中的表达，bzr-h是所有BZR1家族基因的无效突变体。并且bzr-h胚珠的外被膜比bri1-116的外被膜具有更严重的生长缺陷突变体。在一起，我们的发现建立了BRs在调节胚珠发育中的新作用，并暗示BZR1家族转录因子可能通过BRI1依赖性和BRI1依赖性途径调节外被膜的生长。