Fine Mapping Of Two Early Senescence Genes In Rice

Senescence is the final stage of biological growth and development, followed by the process of programmed cell death. The leaveis is an important source of plant organs and provide the energy and a large amount of organic material for plant. Rice is an important crop. Study on mechanism of rice leaf senescence has important significance for rice breeding and plant senescence regulation mechanism.W330 plants showed leaf senescence phenotype from 3-leaf-stage to maturity stage. Compared with wild-type parent Zhonghui8015, the plant height,tiller and blade width of W330 decreased significantly, and the number of productive panicles per plant, the number of spikelets per panicle and seed setting rate were also significantly reduced. All F1 plants generated by crossing early senescence mutant W330 with 02428 showed normal leaf. The segregation ratios of normal plants and early senescence plants in two F2 populations were both 3:1, indicating that the W330 was controlled by a single recessive nuclear gene which was mapped to the short arm of chromosome 3.With developed SSR and Indel markers, the gene was finally narrowed to an interval of 21.5 kb between markers CD-5 and CD-7. Among four ORFs in this region, the LOC_Os03g0131200 encoding a Catalase(OsCATC) was probably the candidate gene. The sequencing analysis and enzyme digestion revealed the variable splicing in the first intron was probably responsible for the early senescence phenotype, which was confirmed by assay of gene expression and enzyme activity. Compared with wild-type parent Zhonghui8015,the content of catalase activity decreased by 47.8% and the content of H2O2 increased by 2.7 times. So, we speculated that the W330 mutant gene was allelic to OsCATC gene. Otherwise, phylogenetic analysis revealed that Os CATC was an independent evolution in rice. Expression analysis of catalase genes by real-time PCR showed that Os CATA and OsCATB have a significant increase in the expression of leaves, while the expression of Os CATC has no significant changes. We speculated that the three highly homologous genes have complementary mechanisms in rice plants.W401 plants showed leaf senescence phenotype from tillering stage to maturity stage. Compared with wild-type parent Zhonghui8015, the plant height,tiller and blade width of W401 decreased significantly, and the number of productive panicles per plant, the number of spikelets per panicle and seed setting rate were also significantly reduced. All F1 plants generated by crossing early senescence mutant W401 with Nipponbare showed normal leaf. The segregation ratios of normal plants and early senescence plants in two F2 populations were both 3:1, indicating that the W401 was controlled by a single recessive nuclear gene which was mapped to the short arm of chromosome 7.With developed SSR and Indel markers, the gene was finally narrowed to an interval of 265.2 kb between markers DT-31 and DT-37. Among fourteen ORFs in this region, the G10 encoding a Methyl transferase was probably the candidate gene. The sequencing analysis revealed the fragment deletion in the first intron was probably responsible for the early senescence phenotype. Compared with wild-type parent Zhonghui8015,the W401 mutant at the heading stage after the chlorophyll content decreased rapid ly, the degradation rate of the protein to be faster than the wild type, SOD and MDA contents increased significantly with time. Dark induced experimental discovery, mutant W401 not affected by dark induced senescence.TEM observation revealed that the mutant and premature senescence of chloroplast development are not related.