Phenotype Analysis And Fine Mapping Of SGD1(T),A Small-Grain Dwarfness Mutant In Rice(Oryza Sativ,L.)

Plant height, directly related to production of rice, is one of the most important agronomic traits of rice. Too high plant would easily result in plant lodging and decreased yield. Appropriate dwarfism can avoid lodging and gain high yield. Researches on the dwarfism are helpful to increase the diversity of dwarf resources, avoid the uniform dwarf rice variety, and also to pave the way to the breakthrough of rice breeding production. Thus it is very important to identify new dwarfism phenotype, characterize their dwarf genes, and finally make use of these genes.In this study, a small grain and dwarf mutant, temporarily designated sgdl(t), hasbeen identified from the T-DNA insertion mutant lines of Nipponbare. Based on a systematic analysis of phenotype, combined with physiological and biochemical analysis, the mechanism underlying the dwarf was discussed. Finally, the gene was fine mapped through map-based cloning. The important results are as follows:(1) Plant height of, sgd1(t) was35cm at maturity, about34.31%of that of the wild-type Nipponbare (110cm). Compared with WT, panicle and all nodes are shortened in sgd1(t), resulting in dwafness. In addition, sgd1(t) showed small round grain, thick and dark yellow hull, short and broad leaves with, dark green clolor and increased chlorophyll content, short and compact spikes, the slightly increased number of tillers, delayed heading date and shortened flowering time, poor fertility and low seed setting;(2) Scanning electron microscope analysis of cellular morphology of stem and hull showed that compared to Nipponbare, cells in sgd1(t) stem failed to form normal cell line. Changes in cell shape directly led to the dwarfness of plants. In addition, epidermal cells in hull were tightly packed with irregular shape, resulting in overall cell showing small protrusions. Cell development is not normal in cross-section of the hull, with changed cell morphology. This irregular cell morphology led to confusion in cell arrangement, which resulted in coarse skin and thickness of sgd1(t) hull. (3) Through different concentration gradients of GA3and BL treatments, sgd1(t) can be restored to a phenotype similar to WT at a concentration of10-4(M). Therefore, sgd1(t) was a GA-sensitive dwarf mutant. Whether sgd1(t) gene is associated with defects in GA synthesis still awaits for the determination of endogenous GA content.(4) Genetic analysis showed that the mutant trait was controlled by a single recessive gene, sgd1(t). Using homologous recessive individuals identified in the sgdl (t)fPusher F2population in2010and the sgdl(y)/Pusher F2:3population in2011, sgd1(t) was eventually located in the553kb region around the telocentromere on the short arm of chromosome9.