The Fine Mapping And Gene Cloning Analysis For A Dominant Minute-grain Gene, Mi(3)t In Oryza. Sativa.

As an important factor of rice production, Grain length also impacts on rice appearance quality and worth of further researches on its molecular level. At the same time, cloning the major grain-length genes will absolutely benefit the better understanding of the mechanisms of grain development, grain-length regulation, as well as determinant programs of grain weight in rice. Moreover, it will also enhance the efficiency of rice quality improvement. In this research, a completely dominant minute-grain gene, designated as Mi3(t), was studied with the approach of classic map-based cloning strategy. The main results were presented as follows:1. Genetic analysis for minute grain: Through investigations and genetic analysis in three genetic populations, as Shuhui 527/Y34, Shuhui 881/Y34 and 9311/Y34, we found that the grain-length trait of Y34 was controlled by a completely dominant minute-grain gene. Further studies indicated that the minute-grain gene mainly controlled the grain length trait by remarkably shortening 35.7%-47.4% of grain length. Meanwhile, we also found that the minute-grain gene also resulted in the improvement of 1000-grain weight, but not in the phenotypes of round grain, low production and later flowering.2. Molecular mapping of the minute grain gene: F2 populations including Shuhui527/Y34, in which there were 112 recessive individuals, and Shuhui 88a/Y34, in which there were 261 recessive individuals, were analyzed with 841 pairs of SSR makers. By Shuhui 527/Y34 F2 population, Mi3(t) was mapped on Chromosome 3 between the SSR makers RM282 and RM411, with the genetic distance of 6.4cM and 4.9cM, respectively. Furthermore, we mapped Mi3(t) by Shuhui881/Y34 F2 population between RM282 and RM6283 on Chromosome 3 with the genetic distance of 5.1cM and 0.9cM, respectively. As two minute grain gene, Mi/Mil and Mik/Mi2, were named in previous studies, minute grain gene studied in present paper was temporarily designed as Mi3(t).3. Fine mapping of Mi3(t): 778 recessive individuals(long grain individuals) from 9311/Y34 F2 population were further analyzed to narrow the Mi3(t) locus. Mi3(t) was first mapped on chromosome 3 between RM6881 and RM6283 in this population, with the genetic distance of 0.5cM and 3.6cM.