Specific expression in reproductive tissues and fate of a mitochondrial sterility-associated protein in cytoplasmic...

In common bean, cytoplasmic male sterility has been associated with a unique sequence found in the mitochondrial genome, designated pvs (for Phaseolus vulgaris sterility sequence). Within the pvs sequence, two open reading frames are encoded, ORF98 and ORF239. We have raised rabbit polyclonal antibodies against Pvs-ORF239 to evaluate the role of this putative male sterility-associated protein. Histological investigation of pollen development revealed that in the male-sterile bean line, callose deposition was abnormal and microspores remained as tetrads as previously reported. Pvs-ORF239 was found to be localized within the reproductive tissues of the male-sterile bean line, in contrast to all other cytoplasmic male sterility systems studied to date. This protein was associated with mitochondria, the callose layer, and developing primary cell walls during microsporogenesis. Expression of pvs-orf239 was not detected in fertile plants containing restorer gene Fr2. These observations, together with previous reports, suggest that nuclear restorer gene Fr2 interferes with expression of the pvs region post-transcriptionally.