Ca 2+ Deficiency Triggers Panicle Degeneration in Rice Mediated by OsCAX1a

Increasing the yield of rice has always been a primary purpose of rice breeding. However, panicle degeneration, a complex characteristic regulated by many genes and commonly encountered in rice production, seriously reduces the yield. 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. Cellular and physiological analyses revealed that the apical panicle in ym48 undergo programmed cell death, accompanied by accumulation of higher levels of peroxide. Following, the OsCAX1a gene responsible for Ca transportation was identified and a highly conserved A to G substitution was noted at the 190 nucleotide in ym48, which damaged Ca transport ability seriously. Through hydroponics assay and Ca quantified, we found that Ca transportation and distribution from underground part to apical tissues was blocked and over-accumulated in mutant stem. In general, this Ca deficiency mediated by OsCAX1a induced peroxide accumulation and resulted to programmed cell death in apical panicle of ym48 mutant. Our results demonstrated the essential role of OsCAX1a in Ca transportation and distribution, and laid a foundation to further explore the genetic and molecular mechanisms of panicle development and differentiation in rice.