This study characterizes a brittle culm (bc88) mutant of rice (Oryza sativa L.) obtained by ethylene methylsulfonate (EMS)-induced mutagenesis of Wuyunjing 7. The bc88 mutant exhibits a diversity of pleiotropic phenotypes, including brittle culm at the whole-plant growth stages, withered leaf tips at the seedling stage, and 18-d delay in heading date at the mature stage. Genetic analysis indicates that the bc88 mutant is controlled by a single recessive nuclear gene. The mutated bc88 gene isolated by map-based cloning contains only one point mutation in the 5th exon relative to its wild-type BC88 (LOC_Os09g25490 and Os09g0422500), leading to an amino acid change from P to L in bc88 plants. Alignment of the putative protein sequence with its homologs indicates that the mutation is located in the conserved region of the sequence. Detection of the transcription level of BC88 in rice plants shows that the expression level of BC88 is higher in spikes and culms than in leaves, roots, and leaf sheaths. These contribute to understanding of the molecular mechanism of cellulose synthesis. The target gene BC88 can be a useful tool in molecular marker-assisted selection for rice culm trait breeding.
RAO YuChunYANG YaoLongXIN DeDongLI XiaoJingZHAI KaiEnMA BoJunPAN JianWeiQIAN QianZENG DaLi
Plant height and tillering are crucial factors determining rice plant architecture and influencing rice grain production. In this study, multi-tillering dwarf1(mtd1), a stable multi-tiller and dwarf mutant, was screened from the ethylmethane sulfonate-treated japonica rice variety Wuyunging7. Compared with the wild type, mtd1 mutant exhibited pleiotropic phenotypes, including dwarfism, more tillers, brittle culms and delayed heading date.By employing map-based cloning strategy, the gene MTD1 was finally mapped to an approximately 66-kb region on the short arm of chromosome 9. Sequencing results showed that the gene LOC_Os09g02650(BC12) in mtd1 mutant had a single nucleotide substitution(G to A), which generated a premature translation stop. Over-expressing MTD1/BC12 coding sequence rescued all the phenotypes of mtd1 mutants including plant height and tillers, which confirms that BC12 is the mutated gene in mtd1 mutant.Quantitative reverse transcription-PCR analysis showed that MTD1/BC12 could negatively regulate the expression of MONOCULM 1, IDEAL PLANT ARCHITECTURE1 and Tillering and Dwarf 1, and control rice tillering. Remarkably, a-amylase activity analysis and gibberellic acid(GA)treatment showed that the dwarf phenotype of mtd1 mutant was dependent on GA biosynthesis pathway. These results facilitated to further uncover the molecular mechanism of the growth and development in rice.
