Deng, XJ; Sun, XQ; Wan, CM; Wang, B; Wang, PR; Xiao, YH
A yellow-green leaf mutant ygl98 was isolated by ethyl methane sulfonate (EMS) mutagenesis. The whole plant exhibited yellow-green character throughout the growing period. The contents of chlorophyll and carotenoid decreased by 45.3% and 45.6%, respectively, compared with its wild-type parent 10079. At maturity stage, the number of productive panicles per plant, seed-setting rate, and plant height of the mutant were reduced by 14.4%, 10.7%, and 7.4%, respectively. Under electron microscope, the chloroplasts in the ygl98 mutant were out-of-shape. A lot of cystic structures and poor thylakoids were observed in the chloroplasts of the ygl98 mutant, and grana stacks appeared to be less dense compared to those of the wild type. Genetic analysis showed that the yellow-green leaf character of the ygl98 mutant was controlled by one pair of recessive nuclear genes. Genetic mapping of the mutant gene was conducted using 771 yellow-green leaf individuals from the F2 mapping population of ygl98/Zhefu 802. Finally, the mutant gene was mapped between insert/deletion (InDel) markers I3 and I4 on the long arm of chromosome 3 with the genetic distances of 0.07 cM and 0.19 cM, respectively. The physical distance between the 2 markers was 44.2 kb harboring 8 predicted genes annotated. Sequencing analysis of these candidate genes between the mutant and its wild type revealed that the single base change (G1 522A) of the gene for magnesium-chelatase ChlD subunit resulted in a missense mutation (A508T) in the encoded product. The same gene mutation caused by OsChlD (Chlorina-1) was documented previously. The Chlorina-1 mutant displays a severe yellowish-green leaf phenotype only at seedling stage, and the abnormal leaf color is first observed on the leaves of 2- to 3-week-old seedlings, while the ygl98 mutant exhibits yellow-green character throughout the growing period. The different phenotypes of the 2 mutants may be caused by the different mutational sites of OsChlD genomic sequence. 摘要 通过EMS诱变获得1份遗传稳定的水稻黄绿叶突变体ygl98, 该突变体整个生育期呈黄绿色。与野生型相比, 突变体的叶绿素和类胡萝卜素含量分别下降45.3%和45.6%, 有效穗数和结实率分别减少14.4%和10.7%, 株高降低7.4%。透射电镜观察表明, ygl98突变体的叶绿体形状不规则, 叶绿体中有许多空的囊泡状结构, 类囊体数目减少, 每个基粒仅由少数几个类囊体垛叠而成。遗传分析表明, ygl98的突变性状由1对隐性核基因控制。利用(ygl98/浙辐802) F2作为定位群体, 将突变基因定位在第3染色体长臂InDel标记I3和I4之间, 遗传距离分别为0.07 cM和0.19 cM, 两标记之间的物理距离约为44.2 kb, 此区间内包含8个预测基因。基因组序列分析发现, ygl98突变体在编码镁离子螯合酶ChlD亚基的OsChlD基因编码区第1 522碱基处(位于第10外显子), 碱基G突变为碱基A, 从而造成编码蛋白序列第508位的丙氨酸(Ala)突变成苏氨酸(Thr)。该基因是已报道的水稻黄绿叶基因Chlorina-1的等位基因, 但突变体表型有明显区别, Chlorina-1突变体在2- to 3-周龄幼苗时开始出现黄绿叶, 且该黄绿叶性状仅在苗期表现, 而ygl98突变体整个生育期都表现为黄绿叶, 这可能是OsChlD基因组序列的突变位点不同造成的。
