一个新的水稻D1基因等位突变体的遗传鉴定与基因功能分析

株高是影响水稻产量的一个重要性状。本研究从水稻稻瘟病普感品种丽江新团黑谷(LTH)经甲基磺酸乙酯(EMS)诱变群体中分离出一个遗传稳定的小粒矮化突变体LTH-m3。该突变体是赤霉素(GA)和油菜素内酯(BR)相关突变体,它对外源GA(GA_3)不敏感,对外源BR(eBL)的敏感性较野生型显著降低。遗传分析、基因克隆和转基因互补实验确认,该突变体是一个新的d1基因等位突变体,其D1基因在第6个外显子与内含子接合处发生单碱基突变(G~(2522)→A~(2522)),导致第6外显子被选择性剪切及Gα蛋白翻译提前终止,从而造成LTH-m3小粒矮化突变表型。进一步的研究表明,该突变体D1基因突变引起SD1和SLR1等基因表达的显著改变,因而影响植株细胞内GA和BR反馈调节功能和信号传递。突变体LTH-m3弥补了LTH植株过高、茎秆软和极易倒伏等缺陷,可作为LTH的改良系在今后水稻稻瘟病研究中加以利用,其功能突变基因的鉴定为深入研究水稻Gα蛋白的功能及激素信号途径提供了新的材料。

Genetic Identification of a New D1-allelic Mutant and Analysis of Its Gene Function in Rice

Plant height is one of important traits for rice yield. One genetically stable rice mutant, LTH-m3, was isolated from the cv. Lijiangxintuanheigu (LTH)-derived mutant population by mutagenesis using ethylmethane sulfonate (EMS). LTH-m3 was involved in the pathway of gibberellic acid (GA) and brassinosteroid (BR), and showed no sensitiveness to exogenous GA (GA₃) and significantly reduced sensitiveness to exogenous BR (eBL) compared with the wild type. The genetic analysis, gene cloning and transgenic complementary test confirmed that LTH-m3 was a new d1-allelic mutant with small grain and dwarf phenotypes, and a single base was mutated (G²⁵²²→A²⁵²²) in the functional dwarf gene D1 at the conjunction site of its sixth exon and intron, which caused excision of the sixth exon in mRNA and premature termination of the D1 encoded Gα protein, resulting in mutated phenotypes in the mutant. The further study showed that the D1 mutation caused obvious expression change of some dwarf genes such as SD1 and SLR1 in the mutant, and could affect the GA and BR pathways in their feedback regulations and signaling transductions in plant cells. The mutant overcome the defects of the universally blast-susceptible cv. LTH, such as too tall plant, soft stem and easy lodging, and could be utilized as an improved substitute of LTH in the future rice blast researches. The mutated D1 gene identified from the LTH-m3 mutant may be useful for further study of Gα functions and signaling pathway of GA and BR.