Comparison Between QTLs for Chlorophyll Content and Genes Controlling Chlorophyll Biosynthesis and Degradation in Japonica Rice

The objectives of this study were to understand the expression patterns of chlorophyll content-related genes at different growth stages of rice (Oryza sativa L.) and to disclose the genetic mechanism of stay-green at later stage. Quantitative trait loci (QTLs) controlling chlorophyll content at tillering, heading, and maturity stages were located using 126 recombinant inbred lines (RILs) derived from a cross between 2 japonica rice cultivars, Shennong 265 and Lijiang Xintuanheigu. A total of 22 QTLs for chlorophyll content were identified, of which 5 loci were expressed at tillering stage, 7 at heading stage, and 10 at maturity stage. These QTLs were located on all the rice chromosomes except chromosome 5. According to the comparison between the locations of these QTLs and genes underlying the key enzymes of chlorophyll biosynthesis and degradation, relatively rich QTLs for chlorophyll biosynthesis and degradation at earlier stage were located in the regions harboring the loci for chlorophyll content. With the process of plant growth, more QTLs were detected but only a few of them were involved in chlorophyll biosynthesis and degradation. These results suggest that the expression levels of most genes/QTLs for chlorophyll biosynthesis or degradation were not different at earlier stage but the expression levels of specific key genes were increased at later stage. Therefore, the genetic basis for stay-green is proposed in 2 pathways: increase of transcripts for chlorophyll biosynthesis-related genes and decrease of expression for chlorophyll degradation genes.

摘 要为剖析水稻叶绿素不同时期的表达规律及后期持绿的遗传机制, 以沈农265和丽江新团黑谷的粳-粳交重组自交系为材料, 对水稻分蘖期、抽穗期和成熟期的叶绿素含量以及生育后期的持绿能力进行QTL定位分析。检测到5个控制分蘖期叶绿素含量的QTL、7个控制水稻抽穗期叶绿素含量的QTL和10个控制成熟期叶绿素含量的QTL, 分布在除第5染色体以外的11条染色体上。比较它们与编码叶绿素合成及降解过程中的重要酶的基因发现, 虽然生育前期检测到的QTL较少, 但对应的叶绿素合成降解相关基因却较多。随生育期的推移, 检测到的QTL数目增多, 但对应的叶绿素合成降解相关基因却减少。暗示生育前期大多数叶绿素合成(降解)相关基因表达的水平差异不大, 后期控制叶绿素合成降解的个别关键基因表达水平增加。并以此为基础提出了叶片生育后期持绿的两种可能遗传基础。