State Key Laboratory of Plant Physiology and Biochemistry, College of Biological Sciences, China Agricultural University, Beijing, 100193, China.
New Phytol. 2021 Dec;232(5):2057-2070. doi: 10.1111/nph.17719. Epub 2021 Sep 25.
Indole-3-acetic acid (IAA) is a predominant form of active auxin in plants. In addition to de novo biosynthesis and release from its conjugate forms, IAA can be converted from its precursor indole-3-butyric acid (IBA). The IBA-derived IAA may help drive root hair elongation in Arabidopsis thaliana seedlings, but how the IBA-to-IAA conversion is regulated and affects IAA function requires further investigation. In this study, HOMEOBOX PROTEIN 24 (HB24), a transcription factor in the zinc finger-homeodomain family (ZF-HD family) of proteins, was identified. With loss of HB24 function, defective growth occurred in root hairs. INDOLE-3-BUTYRIC ACID RESPONSE 1 (IBR1), which encodes an enzyme involved in the IBA-to-IAA conversion, was identified as a direct target of HB24 for the control of root hair elongation. The exogenous IAA or auxin analogue 1-naphthalene acetic acid (NAA) both rescued the root hair growth phenotype of hb24 mutants, but IBA did not, suggesting a role for HB24 in the IBA-to-IAA conversion. Therefore, HB24 participates in root hair elongation by upregulating the expression of IBR1 and subsequently promoting the IBA-to-IAA conversion. Moreover, IAA also elevated the expression of HB24, suggesting a feedback loop is involved in IBA-to-IAA conversion-mediated root hair elongation.
吲哚-3-乙酸（IAA）是植物中主要的活性生长素形式。除了从头合成和从其共轭形式释放外，IAA 还可以从其前体吲哚-3-丁酸（IBA）转化而来。IBA 衍生的 IAA 可能有助于驱动拟南芥幼苗根毛伸长，但 IBA 到 IAA 的转化如何被调节以及如何影响 IAA 功能需要进一步研究。在这项研究中，鉴定了同源盒蛋白 24（HB24），它是锌指-同源结构域（ZF-HD）家族蛋白中的转录因子。HB24 功能丧失时，根毛生长缺陷。鉴定吲哚-3-丁酸响应 1（IBR1）为 HB24 控制根毛伸长的直接靶标，其编码参与 IBA 到 IAA 转化的酶。外源 IAA 或生长素类似物 1-萘乙酸（NAA）都可以挽救 hb24 突变体的根毛生长表型，但 IBA 不能，这表明 HB24 在 IBA 到 IAA 的转化中起作用。因此，HB24 通过上调 IBR1 的表达，从而促进 IBA 到 IAA 的转化，参与根毛伸长。此外，IAA 还提高了 HB24 的表达，表明 IBA 到 IAA 转换介导的根毛伸长涉及到一个反馈回路。
