Abstract
We report the characterization of new alleles of srs3 , srs3-2 and srs3-3 , which set small and round seeds in rice. SRS3 was grouped into the kinesin 13 family. SRS3 was consisted with 12 exons and the SRS3 protein with 819 amino acids. The kinesin-motor domain containing ATPase activity locates in the region from third exon to tenth exon. The previously reported srs3-1 mutant caused one base substitution in the ninth exon, which resulting in the 1 amino acid substitution from leucine to phenylalanine. The srs3-2 mutant caused one base substitution in the region which may be concerned to a splicing between exon 11 and intron 11. The transcript containing the abnormal sequence in the region was detected in the srs3-2 mutant. It was shown that the twelfth exon has an important function, because the exon 12 was lost in srs3-2 . The srs3-3 mutant caused one base substitution resulting the generation of a stop codon. As the mutated protein was lost the kinesin motor domain, it was considered that the mutant was a null mutant. Among three alleles of srs3 mutants, the srs3-3 mutant showed the most severe phenotypes, such as erection of panicle and small round seeds.
