Characterization And Mapping Of Three Chlorophyll Metabolism Related Genes In Rice

Chlorophyll contnet is one of the important factors affecting photosynthesis production, which also is one of the most indexes to evaluate photosynthetic capacity of the leaves in plants. Breeding varieties with higher chlorophyll content, photosynthetic capacity and stay green traits is significant for increasing the grain yield of rice. In this study, three genetic populations were used to identify and analysis function from the genes/QTLs related to the chlorophyll metabolism. The main results are as follows:1. A backcross recombinant inbred lines (BILs) derived from the cross between Sasanisiki and Habataki were used to identify QTLs for chlorophyll content at difference stage. Eighteen QTLs were mapped on chromosome 1,2,3,4,5,6,8 and 9 for chlorophyll content, which explaining phenotypic variation range from 8.73% to 47.75%. Among these QTL, the pleiotropic effective QTL qCTH2 was detected on the chromosome 2 between S2068 and C920 in two years. In addition, the analysis of major QTL-BSA and RHL-F2 mapping narrowed the qCTH2 to 1660.8 kb region between markers RM5472 and RM425.2. Based on the above research results, we isolated a spontaneous mutant named thermo-sensitive chlorophyll deficit 1 (tscdl) derived from a backcross recombinant inbred line population. A larger F2 population of 1128 mutant individuals derived from cross tscdl×Habataki was used for gene mapping. Finally, we located the tscdl gene in 34.95 kb region on the long arm of chromosome 2, containing two BAC clones and eight predicted candidate genes. RT-PCR results showed that the transcript levels of components of the chlorophyll content plastid translation and photosynthetic mechanism were significantly affected on the tscdl mutant at lower temperature. CMPG1 protein (LOC Os02g50460) in the chloroplasts with high expression, homologous sequence alignment showed that many similar genes in rice and arabidopsis, and its function were cope with the low or high temperature stress. In addition, characteristics analysis showed that tscdl plants have a yellow leaves with reduced chlorophyll content, but showed no significant differences after the booting stage. When the temperatures below to 24℃, the tscdl mutant showed the most obvious yellowish phenotype. With increasing temperature, the yellowish leaves gradually turned green and approached a normal leaf color, and then tscdl mutant plants had obviously different chloroplast structures and chlorophyll precursor contents, which was not lead to serious decline in yield and quality traits. These results suggest that TSCD1 may be involved in the regulation of chlorophyll content or chloroplast development at low temperature.3. F2 and F23 populations derived from the cross between Shennong0530-9 and Habataki were used to identify QTLs for chlorophyll content. Twenty-five QTLs were mapped on chromosome 1-10 and 12 for chlorophyll content, which the range of individually explaining phenotypic variation range from 4.51% to 47.76%. Among these QTLs, a pleiotropic region (qCJ2, qCH2, qCM2 and qCD2) were detected on the chromosome 2 between STS5 and RM1347. Further analysis indicated that the genetic effect of qCD2 was the main effects of the chlorophyll degradation from joint stage to heading stage, and the major QTL qCD2 was located between RM2770 and RM1358 on the short arm of chromosome 2. Using leaf senescence individual derived from the segregating population F23 and RHL-F2, this region was narrowed down to an interval between RM12353 and RM6367 in an approximately 54.0 kb physical distance, where nine candidate genes were predicted. In the late growth stage, NIL-qCD2 chloroplast structure has been changed significantly, which result from lower chlorophyll content, ultimate index of photosynthetic fluorescence have a significant decreased, which were significantly chlorophyll degradation and chloroplast structure changes correlated with the higher temperature (>26℃), and then the yield and quality was significant affected.4. We isolated a rice spontaneous mutant, lower chlorophyll b 1 (lcbl), from the population cross from Qishanzhan/Akihikari. Under normal growth conditions, lcb1 plants produced yellow leaves with decreased total Chl and Chl b contents, but normal Chl a and Car content. Photosynthetic and fluorescence parameters significantly difference between wild-type and lcbl plants. Compared with its wild type, lcbl had a higher electron transfer rate, a lower photochemical quenching coefficient and significantly reduced grain number, biomass and yield. Through map-based cloning, we located the LCB1 gene in a 117.4 kb region on the chromosome 3, this region close to the centromere and containing 15 predicted candidate genes, RT-PCR result show that its maybe controlling biogenesis and chloroplast biochemical processes.