Fine Mapping and Candidate Gene Analysis of the Leaf-Color Gene ygl-1 in Maize

A novel yellow-green leaf mutant yellow-green leaf-1 (ygl-1) was isolated in self-pollinated progenies from the cross of maize inbred lines Ye478 and Yuanwu02. The mutant spontaneously showed yellow-green character throughout the lifespan. Meanwhile, the mutant reduced contents of chlorophyll and Car, arrested chloroplast development and lowered the capacity of photosynthesis compared with the wild-type Lx7226. Genetic analysis revealed that the mutant phenotype was controlled by a recessive nuclear gene. The ygl-1 locus was initially mapped to an interval of about 0.86 Mb in bin 1.01 on the short arm of chromosome 1 using 231 yellow-green leaf individuals of an F2 segregating population from ygl-1/Lx7226. Utilizing four new polymorphic SSR markers, the ygl-1 locus was narrowed down to a region of about 48 kb using 2930 and 2247 individuals of F2 and F3 mapping populations, respectively. Among the three predicted genes annotated within this 48 kb region, GRMZM2G007441, which was predicted to encode a cpSRP43 protein, had a 1-bp nucleotide deletion in the coding region of ygl-1 resulting in a frame shift mutation. Semi-quantitative RT-PCR analysis revealed that YGL-1 was constitutively expressed in all tested tissues and its expression level was not significantly affected in the ygl-1 mutant from early to mature stages, while light intensity regulated its expression both in the ygl-1 mutant and wild type seedlings. Furthermore, the mRNA levels of some genes involved in chloroplast development were affected in the six-week old ygl-1 plants. These findings suggested that YGL-1 plays an important role in chloroplast development of maize.本研究从玉米自交系Ye478与元武02的杂交后代自交群体中，分离得到一个新型黄绿叶突变体ygl-1（yellow-green leaf-1）。该突变体在整个生育期均持续表现出黄绿叶性状。与野生型Lx7226相比，该突变体的叶绿素与类胡萝卜素（Carotenoid，Car）含量显著降低，叶绿体发育受阻，光合能力下降。遗传分析表明，该突变体表型受一对隐性核基因调控。利用ygl-1与Lx7226杂交构建的F2分离群体中的231株黄绿叶单株，ygl-1位点初步被定位在玉米第1染色体短臂bin 1.01区域，物理区间约0.86 Mb。借助4对新型多态性简单序列重复（Simple Sequence Repeat，SSR）标记，分别利用包含2930株个体的F2作图群体与2247株个体的F3作图群体，将ygl-1位点精细定位至约48 kb的物理区间内。在该48 kb区间内注释得到的3个预测基因中，GRMZM2G007441被预测编码叶绿体信号识别颗粒43（cpSRP43）蛋白，其在ygl-1的编码区存在1个碱基缺失，进而引发移码突变。半定量逆转录聚合酶链反应（semi-quantitative RT-PCR）分析显示，YGL-1在所有检测组织中均为组成型表达，且在ygl-1突变体中，从生长早期至成熟阶段的基因表达水平无显著变化；而光照强度可同时调控ygl-1突变体与野生型幼苗中该基因的表达。此外，在生长6周的ygl-1植株中，部分参与叶绿体发育的基因的mRNA水平发生显著改变。以上研究结果表明，YGL-1在玉米叶绿体发育过程中发挥重要作用。