| Rice grain yield largely depends on the photosynthetic rate. So it is necessary to explore the melocular genetic mechanism underlying leaf chlorophyll (Chl) content, which positively correlated with photosynthesis. Chl content is affected by nitrogen (N) supply because nitrogen is a major component of Chl. In recent years, in order to increase grain yield, modern rice varieties are selected to permit high chemical fertilizers input, including N input. However, the main problems of excessive N supply are the decreasing of N use efficiency, but increasing the cost for agricultural production and leading to environmental hazards. Increasing leaf Chl content under low N supply condition may be an effective way to increase N utilization efficiency.In this study. Using a high-density genetic map of 132 recombinant inbred lines derived from the cross between 93-11 and PA64s, we detected the quantitative trait loci (QTLs) for Chl content of the top three leaves under two nitrogen conditions at two developmental stages. A total of 32 main-effect QTLs located on chromosomes 1, 4,5,6,7,8, and 12 were identified, and these QTLs individually accounted for 6.0-20.8% of the total phenotypic variation. A major QTL qFCC7L affecting the Chi content under low N condition was identified, and its positive allele came from PA64s. This QTL might be associated with the ability to tolerate low N stress in rice. The chromosomal segment substitution line with 93-11 background but containing the corresponding segment from PA64s had a higher SPAD value and photosynthetic rate than 93-11 and showed a lower specific leaf area. We performed fine mapping using a BC4F2 population and finally mapped this QTL to a 124.5 kb interval on the long arm of chromosome 7. Candidate gene analysis showed that there were sequence variations and expression differences in the predicted candidate gene OsPTR4 between the two parents. These results suggest that this QTL may be useful for breeding the rice varieties with higher photosynthetic rate and grain yield. This work also provided a reference for the cloning of this QTL.Chloroplast is a crucial organelle for plant photosynthesis and maintaining normal life activities in higher plants. Although some genes related to chloroplast development and pigment synthesis have been identified or cloned in rice, little is known about the relationship between these genes and abiotic stress response. We identified a novel mutant white stripe leaf 12 (wsl12) affecting pigment synthesis, chloroplast development and abiotic stress response in rice. The mutant phenotype was obvious at seeding and tillering stages, and in response to the temperature. Genetic analysis showed that wsl12 was a recessive mutant in a single nuclear locus. Map-based cloning revealed that the WSL12 locus encoded OsNDPK2, one of the three nucleoside diphosphate kinases (OsNDPKs). WSL12 expressed in all tested tissues, while highly expressed in leaves and young tissues. The WSL12 protein localized to the chloroplast. The wsl12 mutant showed higher superoxide anion level and enhanced sensitivity to abscisic acid (ABA) and salinity. The transcription pattern of many genes involved in Chl biosynthesis, ABA synthesis, light signaling pathway, reactive oxygen species-scavenging pathway and the other two OsNDPKs were altered in the wsl12 mutant. These results indicate that the OsNDPK2 encoded by WSL12 is a multi-functional protein and it plays an important role in chloroplast development and Chl biosynthesis by regulating the expression levels of related genes. In addition, WSL12 also affects the response to abiotic stress and is beneficial to improve crop stress tolerance via molecular breeding method. |
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