Mutation of OsCAX1a Results in Panicle Degeneration in Rice

Background: Rice is one of the most common cereal crops in China. Increasing the yield of rice has always been a primary purpose of rice breeding. However, panicle degeneration in rice, a complex characteristic regulated by many genes and commonly encountered in rice production, seriously reduces the yield. Findings: In this study, we obtained a new apical panicle degeneration mutant named ym48, which exhibits a serious degeneration rate and reduced grain yield in rice. After fine mapping, the OsCAX1a gene responsible for Ca2+ selection and transportation was identified. In the ym48 mutant of the OsCAX1a gene, a A to G substitution was noted at the 190th nucleotide, and the corresponding 64th amino acid was changed from threonine to alanine. Also, the tolerance from Ca2+ stress was damaged due to the mutation. Phylogenetics, protein sequence alignment and motif identification of CAX family members in Arabidopsis and rice indicated that this mutation site was highly conserved and might play an essential role in Ca2+ transportation. Moreover, the OsCAX1a expression pattern was analyzed in rice. qRT-PCR and GUS (β-glucuronidase) staining experiments showed that OsCAX1a was highly expressed in roots, stems and panicles and that its expression increased with panicle development. Conclusions: These results demonstrated that OsCAX1a played an essential role in the regulation of panicle development for the first time and mutation of OsCAX1a would generate the panicle degeneration in rice. This study provided a new view point to explore the mechanism of panicle development and degeneration in rice.