Fine Mapping Of A Clustered Spikelet Gene Cl-4 In Rice

Recently, research of plant floral development has become a new focus both in plant molecular genetics and developental biology areas . Rice is one of the most important crops in the world, and also a model plant for studying of molecular developental biology in monocots. In addition, the rice floral organs provide the basis for grain formation. Therefore, researches on rice floral development show great theoretical significant and practical application value both in molecular developental biology and rice breeding program.In this study, one clustered spikelet mutant:cl-4, isolated from 93-11 (O. sativa ssp. indica) induced by 60Co-γray. The mutant is different from the wild type in phenotype, exhibited no main axis, fewer secondary branches, 2~3 seeds clustered on the top of the primary branchs and malformed seeds. When cl-4 mutant was crossed to a japonica cv Wuyunjing 8, the phenotype of F1 plants were normal, but the ratio of normal plants to mutant plants in F2 population was disordered from the ratio 3:1, the number of mutant plants was dramatically reduced, which may be due to the property of the indica/japonica cross population. The result preliminary suggested the phenotype of clustered spikelet mutant was controlled by a recessive gene. By using map-based cloning, the cl-4 gene was delimited to a 131 kb long region on the long arm of chromosome 4. And there are predicted 19 genes located in the anchored region, we sequenced 8 conceivable genes, sequencing results showed that P450 90B1 gene mutated , one-base (T) deletion in exon1, and bring forward stop codon. And no sequence differences were found in other 7 predicted genes. The results of our analyses preliminary suggested that P450 90B1 gene functions in spikelet development and the branches elongation.. Sequence BLAST revealed that cl-4 gene was a new allele of Dwarf11, which encoded a putative cytochrome P450 protein named CYP724B1, functioning in the biosythesis of Brassinosteroid (BR), controlling the plant height and grain length. However, on the basis of the phenotype of cl-4 mutant with no main axis (or premature degradation), it was deduced that the function of BR also functions in maintenance of Shoot Apical Meristem (SAM).