Haghir Shahrzad, Yamada Koh, Kato Mariko, Tsuge Tomohiko, Wada Takuji, Tominaga Rumi, Ohashi Yohei, Aoyama Takashi
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
Graduate School of Integrated Sciences for Life, Hiroshima University, 1-4-4 Kagamiyama, Higashi Hiroshima 739-5828, Japan.
Plant Cell Physiol. 2025 Mar 31;66(3):384-399. doi: 10.1093/pcp/pcaf006.
Lotus japonicus-ROOT HAIR LESS1-LIKE-1 (LRL1) of Arabidopsis thaliana encodes a basic helix-loop-helix (bHLH) transcription factor (TF) involved in root hair development. Root hair development is regulated by an elaborate transcriptional network, in which GLABRA2 (GL2), a key negative regulator, directly represses bHLH TF genes, including LRL1 and ROOT HAIR DEFECTIVE6 (RHD6). Although RHD6 and its paralogous TFs have been shown to connect downstream to genes involved in cell morphological events, such as endomembrane and cell wall modification, the downstream network of LRL1 remains elusive. We found that a mutation of LRL1 causes a short-root hair phenotype and that this phenotype can be partially rescued by a transgene encoding a glucocorticoid receptor (GR) domain-fused LRL1, LRL1-GR, in the presence of glucocorticoids. Using this conditional rescue system, we identified 46 genes that are activated downstream of LRL1. Among these, the cell wall-related genes were significantly enriched and many of them were found to be immediately downstream of LRL1 without de novo protein synthesis in between. We further analyzed three representative genes, PROLINE-RICH PROTEIN1 (PRP1), PRP3, and XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDOLASE12 (XTH12). Reporter gene analyses showed that these genes are specifically transcribed in root hair cells including those in the root-hypocotyl junction, and that their proteins were localized to the cell wall of elongating root hairs, root hair bulges, and root hair bulge-expecting loci. A T-DNA insertion mutant of PRP3 showed a moderate short-root hair phenotype. Based on these results, LRL1 is likely to promote root hair development throughout the morphogenetic process by activating cell wall-related genes.
拟南芥的日本百脉根根毛缺失1样1（LRL1）编码一种参与根毛发育的碱性螺旋-环-螺旋（bHLH）转录因子（TF）。根毛发育受一个复杂的转录网络调控，其中关键的负调控因子GLABRA2（GL2）直接抑制包括LRL1和根毛缺陷6（RHD6）在内的bHLH TF基因。尽管RHD6及其同源TF已被证明可连接到参与细胞形态事件（如内膜和细胞壁修饰）的下游基因，但LRL1的下游网络仍不清楚。我们发现LRL1突变会导致短根毛表型，并且在存在糖皮质激素的情况下，编码糖皮质激素受体（GR）结构域融合的LRL1（LRL1-GR）的转基因可以部分挽救这种表型。利用这种条件性挽救系统，我们鉴定了46个在LRL1下游被激活的基因。其中，与细胞壁相关的基因显著富集，并且发现它们中的许多基因直接位于LRL1下游，中间没有从头合成蛋白质。我们进一步分析了三个代表性基因，富含脯氨酸蛋白1（PRP1）、PRP3和木葡聚糖内转糖基酶/水解酶12（XTH12）。报告基因分析表明，这些基因在包括根-下胚轴连接处的根毛细胞中特异性转录，并且它们的蛋白质定位于伸长的根毛、根毛凸起和预期根毛凸起的位点的细胞壁。PRP3的T-DNA插入突变体表现出中度短根毛表型。基于这些结果，LRL1可能通过激活与细胞壁相关的基因在整个形态发生过程中促进根毛发育。
