Polyadenylation accelerates the degradation of the mitochondrial mRNA associated with cytoplasmic male sterility in sunflower

In sunflower, PET1-cytoplasmic male sterility is correlated with the presen ce of a novel mitochondrial gene (orf522) located 3' to the atpA gene, The dicistronic atpA-orf522 transcripts are preferentially destabilized in male florets of 'restored to fertility' plants as compared with sterile plants. In this report, we show that atpA-orf522 transcripts may be polyadenylated in vivo at their 3' termini and that a tissue-specific increase in the lev el of polyadenylated atpA-orf522 transcripts correlates with the tissue-spe cific instability of atpA-orf522 mRNAs in male florets of the restored hybr id plants. In addition, we have identified two distinct ribonuclease activi ties in sunflower mitochondria, one of which preferentially degrades polyad enylated as compared with non-polyadenylated RNA substrates corresponding t o the 3' UTR of atpA-orf522 transcripts. These in vivo and irt vitro result s show that polyadenylation is involved in the degradation pathway of the m itochondrial atpA-orf522 transcripts and that polyadenylation can be develo pmentally regulated by a nuclear gene(s) upon restoration of fertility.