Characterization And Mapping Of DES2 In Rice

Rice (Oryza sativa L.) as one of the most important crops, supplies food for about a half of the world's population. Because of the increasing severity of food crisis in the modern world, the importance is conferred on the investigation aiming to improve grain yield. The research on rice genetics can facilitate the improvement of rice production, thus alleviating the crisis.The average number of spikelets per panicle could largely determine rice yield. Five lines of decreased spikelets (des1 to des5), with reduced spikelet number, were isolated by screening the japonica rice cultivar Zhonghua 11 (ZH11) population with des1 to des4 irradiated byγ-ray and des5 mutagenized by EMS, in which des2 was characterized in detail here. The striking phenotype of des2 is the reduction of secondary branches (SB) and lateral spikelets (SP), with that of other branches including tillers and primary branches (PB) relatively modest. A single recessive locus was proved responsible for des2 phenotype by segregation analysis, then was primarily found to be linked with two markers RM3827 and RM528 on the long arm of chromosome 6. Finally, with the generation of newly developed molecular markers and a larger mapping population, des2 was delimited to a～28kb region between markers OsdCAPS2 and OsdCAPS3, while co-segregated with RM20378d. Sequence analysis showed that a point mutation occurred in the coding region of MOC1 gene, leading to a premature translation stop that results in a truncated MOC1 protein with the last 5 residues in C-terminus lost. Therefore, des2 phenotype is probably caused by the mutation of MOC1 gene. Genetic analyses demonstrated that defects in des5 should also result from recessive mutation in a single locus, and that des2 and des5 double mutation exerted significant synergistic effects on axillary branch development. This study will shed new light on the function of MOC1 at molecular level.