抄録
Previously, we isolated SHORT GRAIN 1 (SG1) gene that encodes a novel protein in rice. SG1:OX rice shows a semi-dwarf phenotype with erected leaves reminiscent of brassinosteroid (BR) deficient mutants, however BR-content was comparable with WT. Therefore, it had been suggested that BR response might be repressed in SG1:OX plants. BR response of SG1:OX rice was investigated by lamina inclination assay. SG1:OX rice was insensitive to BR. In addition to short grain phenotype, it showed dense panicle phenotype. We developed a software to measure lengths of grains and internodes from scanned photographic images of panicles. Reduction of elongation of rachis internodes between spikelets appeared to be responsible for the dense panicle phenotype of OX rice. In contrast, RNAi plants that suppress both SG1 and its homologue SGL1 showed elongated grains and internodes between spikelets. In addition, expression of SG1 was predominantly detected in young panicles mainly at lower part of rachises and their branches by analyses of SG1-promoter GUS plants, as well as by RT-PCR. Further, cellular sizes of various organs of OX and WT plants were examined. Despite short organ phenotype, cellular sizes in organs of OX rice were similar to those of WT, implicating that reduction of organ size is mainly caused by reduction of cell numbers. Considering on phenotypes of OX and RNAi plants and its expression pattern, SG1 may repress organ elongation and cell division by repression of BR signaling.
