State Key Laboratory for Conservation and Utilization of Subtropical Agro-bioresources, College of Life Science and Technology, Guangxi University, Nanning 530004, China.
Plant Cell. 2022 Jul 30;34(8):2948-2968. doi: 10.1093/plcell/koac140.
Plants have evolved a lignin-based Casparian strip (CS) in roots that restricts passive diffusion of mineral elements from the soil to the stele. However, the molecular mechanisms underlying CS formation in rice (Oryza sativa), which contains a CS at both the exodermis and endodermis, are poorly understood. Here, we demonstrate that CS formation at the rice endodermis is redundantly regulated by three MYELOBLASTOSIS (MYB) transcription factors, OsMYB36a, OsMYB36b, and OsMYB36c, that are highly expressed in root tips. Knockout of all three genes resulted in a complete absence of CS at the endodermis and retarded plant growth in hydroponic conditions and in soil. Compared with the wild-type, the triple mutants showed higher calcium (Ca) levels and lower Mn, Fe, Zn, Cu, and Cd levels in shoots. High Ca supply further inhibited mutant growth and increased Ca levels in shoots. Transcriptome analysis identified 1,093 downstream genes regulated by OsMYB36a/b/c, including the key CS formation gene OsCASP1 and other genes that function in CS formation at the endodermis. Three OsMYB36s regulate OsCASP1 and OsESB1 expression by directly binding to MYB-binding motifs in their promoters. Our findings thus provide important insights into the mechanism of CS formation at the endodermis and the selective uptake of mineral elements in roots.
植物在根部形成了基于木质素的凯氏带（Casparian strip，CS），以限制矿物质元素从土壤被动扩散到中柱。然而，对于含有内皮层和外皮层 CS 的水稻（Oryza sativa）中 CS 形成的分子机制仍知之甚少。在这里，我们证明了三个 MYB 转录因子 OsMYB36a、OsMYB36b 和 OsMYB36c 冗余调控水稻内皮层 CS 的形成，这些转录因子在根尖高度表达。敲除这三个基因会导致内皮层 CS 完全缺失，并在水培和土壤条件下减缓植物生长。与野生型相比，三重突变体的地上部钙（Ca）水平更高，锰（Mn）、铁（Fe）、锌（Zn）、铜（Cu）和镉（Cd）水平更低。高钙供应进一步抑制了突变体的生长，并增加了地上部的 Ca 水平。转录组分析鉴定了 1093 个受 OsMYB36a/b/c 调控的下游基因，包括关键的 CS 形成基因 OsCASP1 和其他在内皮层形成 CS 中起作用的基因。三个 OsMYB36s 通过直接结合其启动子中的 MYB 结合基序来调节 OsCASP1 和 OsESB1 的表达。因此，我们的研究结果为内皮层 CS 形成和根系矿物质元素选择性吸收的机制提供了重要的见解。
