MULTI-TILLERING DWARF1, a new allele of BRITTLE CULM 12, affects plant height and tiller in rice

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, α-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.