Deletion of the OsLA1 Gene Leads to Multi-Tillering and Lazy Phenotypes in Rice

Plant architecture, one of the key factors that determine grain yield in rice, is mainly affected by components such as plant height, tiller number, and panicle morphology. For this paper, we obtained a multi-tillering and lazy mutant from a japonica rice cultivar, Wuyunjing 7 (WYJ7), via treatment with a heavy ion beam. Compared to WYJ7, the mutant showed a significant increase in tiller angle, tiller number, number of primary and secondary branches, and number of grains; however, the plant height and grain thickness of the mutant was significantly decreased. Phenotypic analysis of the F1 hybrids revealed that the multi-tillering and lazy mutant phenotypes were regulated by a recessive gene. The segregation ratio of 1:3 of the mutant phenotype and the wild-type plant in the F-2 population indicated that the former was controlled by a single gene named Multi-Tillering and Lazy 1 (MTL1). Bulked segregant analysis was performed using the individual plants with extremely typical tiller angles in the F-2 population. The MTL1 gene was initially mapped within a region of 5.58-17.64 Mb on chromosome 11. By using the F-2 segregated population for fine mapping, the MTL1 gene was ultimately fine mapped within the range of 66.67 kb on chromosome 11. The analysis of genes in this region revealed the presence of the previously identified LAZY1 (LA1) gene. Genomic PCR amplification and semi-quantitative RT-PCR assays showed that the LA1 gene could not be amplified and was not expressed, thus indicating that the MTL1 gene might be identical to the LA1 gene. This study suggests that the multi-tillering and lazy mutant phenotypes might be caused by the deletion of LA1 function. This finding can guide further investigations on the functional mechanisms of the LA1 gene, thus enriching the theoretical knowledge of plant architecture in relation to rice.