Causes of cytoplasmic male sterility (CMS) in plants have been studied for two decades, and mitochondrial chimeric genes have been predicted to induce CMS. However, it is unclear what happens after CMS-associated proteins accumulate in mitochondria. In our previous study of microarray analysis, we found that 140 genes are aberrantly regulated in anthers of CW-type CMS of rice (Oryza sativa L.). In the present study, we investigated DCW11, one of the down-regulated genes in CW-CMS encoding a protein phosphatase 2C (PP2C). DCW11 mRNA was preferentially expressed in anthers, with the highest expression in mature pollen. As predicted by the N-terminal sequence, DCW11 signal peptidegreen fluorescent protein (GFP) fusion protein was localized in mitochondria. Knockdown of DCW11 in wild-type rice by RNA interference caused a major loss of seed-set fertility, without visible defect in pollen development. Since this knockdown phenotype resembled that of CW-CMS, we concluded that the down-regulation of DCW11 is correlated with CW-CMS. This idea was supported by the up-regulation of alternative oxidase 1a (AOX1a), which is known to be regulated by mitochondrial retrograde signaling, in DCW11 knockdown lines. Down-regulation of DCW11 and up-regulation of AOX1a were also observed in two other types of rice CMS. Our result indicates that DCW11 could play a role as a mitochondrial signal transduction mediator in pollen germination. 6
