Fertility restoration mechanisms in S-type cytoplasmic male sterility of maize (Zea mays L.) revealed through expression differences identified by cDNA microarray and suppression subtractive hybridization

Cytoplasmic male sterility (CMS) is thought to be due to an incompatibility of 2 genomes that results in pollen abortion. In CMS-S of maize (Zea mays L.), mitochondrialorf355-orf77 and the nuclear restorer of fertility interact to control fertility of gametophytes. Numerous studies demonstrated thatRf3 can regulate nuclear and mitochondrial gene expression and shows pleiotropic effects on the transcriptional level. Little is known, however, about the alteration of the global expression profile caused byRf3 substitution ofrf3 under S cytoplasm or about molecular fertility restoration mechanisms. In this study, cDNA microarray and suppression subtractive hybridization were used to reveal differentially expressed genes during pollen development by comparing a set ofRf3/rf3 near isogenic lines. A total of 137 tentative unique genes (TUGs) were identified at the transcriptional level. On the basis of functional category analysis, these TUGs were involved in a broad range of cellular and biochemical activities, including metabolism, cell structure, cell defense, and apoptosis, as well as signal transduction pathways. Northern blot analysis using 5 representative clones as probes confirmed differential expression among S-(Rf3) and S-(rf3). Especially in S-(Rf3), the expression patterns of genes associated with electron or H+ conduction and antiapoptosis genes (e.g., VADC2, BI-1, cystatin, 14-3-3) are distinctly different from in S-(rf3). Together with normalization of cellular and biochemical activities in S-(Rf3), we proposed thatRf3 might regulate accumulation of nuclear and mitochondrial gene transcripts directly or indirectly to inhibit multiple programmed cell death pathways in S-type cytoplasm allowing the normal developmental pathways to unfold.