Activation of Mitochondrial orf355 Gene Expression by a Nuclear-Encoded DREB Transcription Factor Causes Cytoplasmic Male Sterility in Maize

Coordination between mitochondria and the nucleus is crucial for fertility determination in plants with cytoplasmic male sterility(CMS).Using yeast one-hybrid screening,we identified a transcription factor,ZmDREB1.7,that is highly expressed in sterile microspores at the large vacuole stage and activates the expression of mitochondria-encoded CMS gene orf355.Δpro,a weak allele of ZmDREB1.7 with the loss of a key unfolded protein response(UPR)motif in the promoter,partially restores male fertility of CMS-S maize.ZmDREB1.7 expression increases rapidly in response to antimycin A treatment,but this response is attenuated in theΔpro allele.Furthermore,we found that expression of orf355 in mitochondria activates mitochondrial retrograde signaling,which in turn induces ZmDREB1.7 expression.Taken together,these findings demonstrate that positive-feedback transcriptional regulation between a nuclear regulator and a mitochondrial CMS gene determines male sterility in maize,providing new insights into nucleus-mitochondria communication in plants.