Genetic Mapping of Rolled Leaf and Spotted Leaf Mutants in Rice

Abstract

Leaves are the organ for photosynthesis, respiration and transpiration, and have a major effect on growth and development related to crop yield. Therefore, morphological characteristics of leaf such as structure, shape and color are important agronomic traits in rice (Oryza sativa L.) breeding for ideal plant type.

To understand the genes related to leaf and those of regulations, we obtained two new leaf-related mutants, rolled leaf mutant and spotted leaf mutant, from Ilpum (Oryza sativa japonica) by the treatment of ethyl methane sulfonate (EMS). The rolled leaf mutant was observed to have increased bulliform cell number and size, and led to the outcurved leaf rolling. The spotted leaf mutant displayed brown and white spots from early vegetative stage.

The phenotypes of the F1 plants derived from the cross between these mutants and wild-type plants were normal. In each F2 population, segregation ratio between the wild-type and the mutant type was 3:1. This genetic analysis indicated that each mutant phenotype was controlled by single recessive gene. Bulked segregant analysis (BSA) and genetic mapping were conducted using F2 population developed from the cross between each of mutants and Milyang23 (Oryza sativa indica). According to the results, the rolled leaf gene was located on the long arm of chromosome 2 between the flanking markers 2125f and 2126b (122kb) and the spotted leaf gene was located on the long arm of chromosome 5 between the flanking markers S05105 and S05112 (2.2Mb). In order to search for candidate genes and causal SNP positions rapidly, whole-genome sequencing data of Ilpum and bulked F2 progenies displaying the mutant phenotype were used. Through the combination of the BSA and SNP analysis, two candidate genes of rolled leaf mutant and a few candidate SNP positions of spotted leaf mutant were identified. This study will contribute to the further study of leaf-related mechanism in rice, and confirmation of each candidate genes is in progress.