Genetic analysis and fine mapping of an enclosed panicle mutant esp2 in rice (Oryza sativa L.)

The phenomenon of panicle enclosure in rice is mainly caused by the shortening of uppermost internode. Elucidating the molecular mechanism of panicle enclosure will be helpful for solving the problem of panicle enclosure in male sterile lines and creating new germplasms in rice. We acquired a monogenic recessive enclosed panicle mutant, named as esp2 (enclosed shorter panicle 2), from the tissue culture progeny of indica rice cultivar Minghui-86. In the mutant, panicles were entirely enclosed by flag leaf sheaths and the uppermost internode was almost completely degenerated, but the other internodes did not have obvious changes in length. Genetic analysis indicated that the mutant phenotype was controlled by a recessive gene, which could be steadily inherited and was not affected by genetic background. Apparently, ESP2 is a key gene for the development of uppermost internode in rice. Using an F(2) population of a cross between esp2 and a japonica rice cultivar Xiushui-13 as well as SSR and InDel markers, we fine mapped ESP2 to a 14-kb region on the end of the short arm of chromosome 1. According to the rice genome sequence annotation, only one intact gene exists in this region, namely, a putative phosphatidylserine synthase gene. Sequencing analysis on the mutant and the wild type indicated that this gene was inserted by a 5287-bp retrotransposon sequence. Hence, we took this gene as a candidate of ESP2. The results of this study will facilitate the cloning and functional analysis of ESP2 gene.