ELONGATED HYPOCOTYL 5 (HY5) is a major light-associated transcription factor involved in plant growth and development. In Arabidopsis (Arabidopsis thaliana), the role of HY5 is very well-defined in regulating primary root growth and lateral root formation; however, information regarding its role in root hair development is still lacking, and little is known about the genetic pathways regulating this process. In this study, we investigated the role of HY5 and its associated components in root hair development. Detailed analysis of root hair phenotype in wild-type (WT) and light signaling mutants in light and dark conditions revealed the importance of light-dependent HY5-mediated root hair initiation. Altered auxin levels in the root apex of the hy5 mutant and interaction of HY5 with promoters of root hair developmental genes were responsible for differential expression of root hair developmental genes and phenotype in the hy5 mutant. The partial complementation of root hair in the hy5 mutant after external supplementation of auxin and regaining of root hair in PIN-FORMED 2 (pin2) and PIN-FORMED 2 (pin3) mutants after grafting suggested that the auxin-mediated root hair development pathway requires HY5. Furthermore, miR397b overexpression (miR397bOX) and CRISPR/Cas9-based mutants (miR397bCR) indicated miR397b targets genes encoding Reduced Residual Arabinose (RRA1/RRA2), which in turn regulate root hair growth. The regulation of the miR397b- (RRA1/RRA2) module by HY5 demonstrated its indirect role by targeting root hair cell wall genes. Together, this study demonstrated that HY5 controls root hair development by integrating auxin signalling and other miRNA-mediated pathways.

中文翻译：

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包含 ELONGATED HYPOCOTYL5、microRNA397b 和生长素相关因子的网络调节拟南芥根毛生长


ELONGATED HYPOCOTYL 5 (HY5) 是参与植物生长和发育的主要光相关转录因子。在拟南芥（Arabidopsis thaliana）中，HY5 在调节初生根生长和侧根形成方面的作用非常明确；然而，关于其在根毛发育中的作用的信息仍然缺乏，并且对于调节这一过程的遗传途径知之甚少。在这项研究中，我们研究了 HY5 及其相关成分在根毛发育中的作用。对光照和黑暗条件下野生型 (WT) 和光信号突变体根毛表型的详细分析揭示了光依赖性 HY5 介导的根毛起始的重要性。 hy5突变体根尖生长素水平的改变以及HY5与根毛发育基因启动子的相互作用是导致hy5突变体中根毛发育基因和表型差异表达的原因。外部补充生长素后hy5突变体中根毛的部分补充以及嫁接后PIN-FORMED 2 (pin2)和PIN-FORMED 2 (pin3)突变体中根毛的恢复表明生长素介导的根毛发育途径需要HY5。此外，miR397b过表达（miR397bOX）和基于CRISPR/Cas9的突变体（miR397bCR）表明miR397b靶向编码减少残留阿拉伯糖（RRA1/RRA2）的基因，这反过来又调节根毛生长。 HY5 对 miR397b-(RRA1/RRA2) 模块的调节证明了其通过靶向根毛细胞壁基因的间接作用。总之，这项研究表明 HY5 通过整合生长素信号传导和其他 miRNA 介导的途径来控制根毛发育。