A Novel Kinesin 13 Protein Regulating Rice Seed Length

Abstract

The causal gene of a novel small and round seed mutant phenotype (srs3) in rice was identified by map-based cloning and named the SRS3 gene. The SRS3 gene was grouped as a member of the kinesin 13 subfamily. The SRS3 gene codes for a protein of 819 amino acids that contains a kinesin motor domain and a coiled-coil structure. Using scanning electron microscopy, we determined that the cell length of seeds in the longitudinal direction in srs3 is shorter than that in the wild type. The number of cells of seeds in the longitudinal direction in srs3 was not very different from that in the wild type. The result suggests that the small and round seed phenotype of srs3 is due to a reduction in cell length of seeds in the longitudinal direction. The SRS3 protein, which is found in the crude microsomal fraction, is highly expressed in developing organs.

The SMALL AND ROUND SEED1 (SRS1/DEP2) gene is involved in the regulation of seed size in rice

“…The cause of the small seed phenotype in the srs3 mutant is mainly due to the reduction of cell length in the lemma (Kitagawa et al, 2010). The SRS3 gene encodes a kinesin 13 protein (Kitagawa et al, 2010).…”

“…Rice yield potential is determined by several factors including seed size (or weight), number of panicles per plant and number of seeds per panicle (Takeda and Matsuoka, 2008;Song and Ashikari, 2008). Among these factors, we have been focusing on the study of seed size and continue to identify regulatory genes (Fujisawa et al, 1999;Tanabe et al, 2005;Kitagawa et al, 2010), in order to understand the molecular mechanisms that underline seed size regulation. Knowledge of these genes could be useful for breeding purpose.…”

“…Causal genes of small (or short) seed phenotype have been identified by us and other research groups through map-based cloning, namely D1 (also named RGA1) encoding the heterotrimeric G protein α subunit (Ashikari et al, 1999;Fujisawa et al, 1999), D11 encoding a cytochrome P450 involved in brassinosteroid (BR) biosynthesis (Tanabe et al, 2005), BRD1 and D2 encoding different types of cytochrome P450 that are also involved in BR synthesis (Hong et al, 2002(Hong et al, , 2003, BRD2 (also named rice Dim/dwf1) encoding an enzyme associated with BR biosynthesis (Hong et al, 2005), D61 (also named OsBRI1) encoding a BR receptor (Yamamuro et al, 2000), and finally SRS3 encoding the kinesin 13 protein (Kitagawa et al, 2010). These studies have shown that both the heterotrimeric G protein signaling pathway and the BR signaling pathway play a major role in the regulation of seed size.…”

“…These studies have shown that both the heterotrimeric G protein signaling pathway and the BR signaling pathway play a major role in the regulation of seed size. During seed formation in rice, it was shown that D1 regulates the cell number (Izawa et al, Edited by Masao Tasaka2010) and SRS3 regulates the cell length (Kitagawa et al, 2010), whereas BR-related genes seem to regulate both cell number and cell elongation (Yamamuro et al, 2000;Hong et al, 2002;Nakamura et al, 2006). Therefore, there are different types of functional genes that regulate seed size through the control of either cell length, cell number, or both.…”

Functional Characterization of Genes/QTLs for Increasing Rice Yield Potential

“…SMALL AND ROUND SEED (SRS3), which encodes a protein of the kinesin 13 subfamily containing a kinesin motor domain and a coiled-coil structure, is strongly expressed in developing organs and regulates rice grain length. The srs3 mutant shows shorter cells compared to the wild type, which causes the small and round seed phenotype [46]. Srs5 encodes alpha-tubulin protein and its mutation produces a semidominant mutant exhibiting similar phenotype with the srs3 mutant [47].…”