Genetic Analysis And Gene Mapping Of A Small Grain Dwarf Mutant In Rice (Oryza Sativa L.)

Rice (Oryza sativa L.) is one of the world’s major food crops. And the plant height is one of the important agronomic traits of rice. So far, more than 70 semidwarf or dwarf plants had been identified. Grain shape is also one of the important agronomic traits of rice as it relates to the quality and appearance of rice yield. In this paper, a spontaneous dwarf mutant, designated d1352, was identified from the indica rice maintainer line 1352.Through the investigation of some major agronomic traits and responses tohormones, etc. of the mutant rice d1352 and wild-type, respectively, the geneticanalysis of the dwarf small grain traits, the fine mapping of the mutant gene d1352 as well as the expression levelof genesrelated to BR’s synthesis pathwaysandsignal transduction,we obtained the following resuLts:1. Anatomical investigation revealed that the plant height and grain length of d1352 decreased by 66 and 36%, respectively, compared with those of wild-type (WT) rice. All mutant internodes were sharply shortened when compared with their WT counterparts, and the relative ratio of each internode suggested a d6-type mutation ofd1352.2. The response toexogenoushormoneanalysis found:The d1352 and WT plants showed similar responses to exogenousGAactive substances GA3 or an inhibitor of GA biosynthesis PP333 and the effect of different concentrations of GA3 on seedling plant height was similar between the WT and d1352.Incomplete darkness, thed 1352mutant showed a typical etiolated phenotype similar to the BR-insensitive mutant.The length of d1352 seedlings coμLd not be elongated with additiveexogenousBRactive substances 24-eBL. Compared toWT,the d1352 mutant showed a significantly reduced response to 24-eBL in both tests of the growth of seminal root and the effect of the bent angles. It is suggested that d1352had normal sensitivity to GA but had reduced sensitivity to BR treatment compared with the WT.3. Investigation of all four F2 popμLations, which were developed by crossing dl352 with the indica rice cμLtivars XS1, MH63 and Hanma and the japonica rice cμLtivar Taishannuo, showed that the segregate ratio of the normal and dwarf plants was 3:1, which indicated that the mutation was controlled by a single recessive gene, named as d1352. All altered traits, such as the plant height and the grain shape, in the d1352 mutant also co-segregated in all the F2 mutant individuals. This resμLt suggests that the D1352 gene elicits pleiotropic effects.4. The mutant gene d1352 was located in a 98-kb region on rice chromosome 3 by employing a map-based cloning strategy. Sequencing comparison revealed a 24-bp insertion in the coding region of a putative U-box E3 ubiquitin ligase (LOC_Os03g13010), which led to the insertion of eight amino acids in the conserved domain of U-box. Linkage analysis in all popμLations showed that the insertion was co-segregated with the dwarf phenotype, indicating that the insertion of LOC_Os03g13010 was responsible for the mutant phenotype.5. The relative expression levels of several BR-related genes were determined in the dl352 and WT plants and theresμLts revealed significant upregμLation in the expression levels of BRD1,OsDWARF4,andOsBZRl but significant downregμLation in the expression levels of D61,BRD2,and Dll in d1352. The loss of function of D1352 significantly affected the expression levels of BR-related genes. This resμLt suggests that D1352 is crucial in the BR signal transduction pathway.In conclusion, we report that the mutation of a U-box E3 ubiquitin ligase reduces BR sensitivity in rice.