Evaluation of the fertility restoring ability of Rf-PPR592 in petunia

Cytoplasmic male sterility (CMS) in petunia is associated with the mitochondrial locus pcf, which encodes a 19.5 kD protein that is expressed in the tapetum of floral buds. A dominant nuclear gene called Restorer of Fertility (Rf) suppresses CMS by dramatically reducing PCF expression. The petunia Rf gene was cloned through a combination of candidate gene approach and transgenic complementation assay. A candidate open reading frame found in a BIBAC2 clone identified from a genomic screen was tested for its ability to restore fertility in petunia CMS lines. The open reading frame contains 592 codons and pentatricopeptide repeat motifs and was therefore designated Rf-PPR592. Green fluorescent protein fused to a putative targeting signal from Rf-PPR592 was imported into the mitochondria. Both sterile and fertile transformants were obtained following Agrobacterium-mediated transformation of PCF protein abundance and pollen production in the progeny of fertile primary transformants. While most transformants were normal, a few exhibited unusual vegetative and reproductive organs.