National Key Facility for Crop Gene Resources and Genetic Improvement, Institute of Crop Science, Chinese Academy of Agricultural Sciences, Beijing, 100081, PR China.
State Key Laboratory of Crop Genetics and Germplasm Enhancement, Jiangsu Plant Gene Engineering Research Center, Nanjing Agricultural University, Nanjing, 210095, PR China.
Plant Sci. 2019 Nov;288:110208. doi: 10.1016/j.plantsci.2019.110208. Epub 2019 Jul 31.
Homeodomain leucine zipper (HD-Zip) proteins are transcription factors that regulate plant development. Bioactive gibberellin (GA) is a key endogenous hormone that participates in plant growth. However, the relationship between HD-Zip genes and modulation of GA biosynthesis in rice remains elusive. Here, we identified a rice mutant, designated as small grain and dwarf 2 (sgd2), which had reduced height and grain size compared with the wild type. Cytological observations indicated that the defective phenotype was mainly due to decreased cell length. Map-based cloning and complementation tests demonstrated that a 9 bp deletion in a homeodomain leucine zipper (HD-Zip) II family transcription factor was responsible for the sgd2 mutant phenotype. Expression of SGD2 was pronounced in developing panicles, and its protein was localized in nucleus. Luciferase reporter system and transactivation assays in yeast suggested that SGD2 functioned as a transcriptional repressor. High performance liquid chromatography assays showed that the endogenous GA level in the sgd2 mutant was dramatically decreased, and exogenous GA recovered the second leaf sheath to normal length. Results of qRT-PCR showed that the expression levels of genes positively regulating GA-biosynthesis were mostly down-regulated in the mutant. Our data identified the role of an HD-Zip transcription factor that affects rice plant development by modulating gibberellin biosynthesis.
同源异型域亮氨酸拉链（HD-Zip）蛋白是一类转录因子，可调节植物的发育。生物活性赤霉素（GA）是一种关键的内源性激素，参与植物的生长。然而，HD-Zip 基因与水稻中 GA 生物合成的调节之间的关系仍不清楚。在这里，我们鉴定了一个水稻突变体，命名为小粒和矮化 2 号（sgd2），与野生型相比，其株高和粒长降低。细胞学观察表明，该缺陷表型主要是由于细胞长度减小所致。基于图谱的克隆和互补测试表明，一个同源异型域亮氨酸拉链（HD-Zip）II 家族转录因子中的 9 个碱基缺失导致了 sgd2 突变体的表型。SGD2 的表达在发育中的穗中明显，其蛋白定位于细胞核中。荧光素酶报告系统和酵母中的转录激活试验表明，SGD2 作为转录阻遏物发挥作用。高效液相色谱分析表明，sgd2 突变体中的内源 GA 水平显著降低，而外源 GA 则使第二叶鞘恢复到正常长度。qRT-PCR 的结果表明，突变体中正向调节 GA 生物合成的基因表达水平大多下调。我们的数据确定了一个 HD-Zip 转录因子的作用，该转录因子通过调节赤霉素的生物合成来影响水稻的发育。
