Crop Biotech Institute and Graduate School of Biotechnology, Kyung Hee University, Yongin, Korea.
Department of Plant Bioscience, Pusan National University, Miryang, Korea.
J Exp Bot. 2020 Sep 19;71(18):5348-5364. doi: 10.1093/jxb/eraa209.
Root meristem activity is the most critical process influencing root development. Although several factors that regulate meristem activity have been identified in rice, studies on the enhancement of meristem activity in roots are limited. We identified a T-DNA activation tagging line of a zinc-finger homeobox gene, OsZHD2, which has longer seminal and lateral roots due to increased meristem activity. The phenotypes were confirmed in transgenic plants overexpressing OsZHD2. In addition, the overexpressing plants showed enhanced grain yield under low nutrient and paddy field conditions. OsZHD2 was preferentially expressed in the shoot apical meristem and root tips. Transcriptome analyses and quantitative real-time PCR experiments on roots from the activation tagging line and the wild type showed that genes for ethylene biosynthesis were up-regulated in the activation line. Ethylene levels were higher in the activation lines compared with the wild type. ChIP assay results suggested that OsZHD2 induces ethylene biosynthesis by controlling ACS5 directly. Treatment with ACC (1-aminocyclopropane-1-carboxylic acid), an ethylene precursor, induced the expression of the DR5 reporter at the root tip and stele, whereas treatment with an ethylene biosynthesis inhibitor, AVG (aminoethoxyvinylglycine), decreased that expression in both the wild type and the OsZHD2 overexpression line. These observations suggest that OsZHD2 enhances root meristem activity by influencing ethylene biosynthesis and, in turn, auxin.
根分生组织的活性是影响根系发育的最关键过程。尽管已经在水稻中鉴定出了几种调节分生组织活性的因素，但对根分生组织活性的增强研究仍然有限。我们鉴定了一个锌指同源盒基因 OsZHD2 的 T-DNA 激活标签系，由于分生组织活性增加，该基因具有更长的初生根和侧根。在过表达 OsZHD2 的转基因植物中证实了这些表型。此外，过表达植株在低养分和稻田条件下表现出增强的籽粒产量。OsZHD2 在茎尖分生组织和根尖中优先表达。对激活标签系和野生型根的转录组分析和定量实时 PCR 实验表明，激活标签系中乙烯生物合成基因上调。与野生型相比，激活系中的乙烯水平更高。ChIP 分析结果表明，OsZHD2 通过直接控制 ACS5 来诱导乙烯生物合成。用乙烯前体 ACC（1-氨基环丙烷-1-羧酸）处理诱导根尖端和中柱处 DR5 报告基因的表达，而用乙烯生物合成抑制剂 AVG（氨基乙氧基乙烯基甘氨酸）处理则降低了野生型和 OsZHD2 过表达系中 DR5 报告基因的表达。这些观察结果表明，OsZHD2 通过影响乙烯生物合成和生长素来增强根分生组织的活性。
