THE PLANT CELL, Vol 1, Issue 11 1121-1130, Copyright © 1989 by American Society of Plant Biologists
Identification of a Mitochondrial Protein Associated with Cytoplasmic Male Sterility in Petunia
H. T. Nivison and M. R. Hanson
Section of Genetics and Development, Cornell University, Ithaca, New York 14853
The petunia fused gene (pcf), which is associated with cytoplasmic male
sterility (CMS), is composed of sequences derived from atp9, coxII, and an
unidentified reading frame termed urfS. To determine whether the pcf gene
is expressed at the protein level, we produced antibodies to synthetic
peptides specified by the coxII and urfS portions of the pcf gene.
Anti-COXII peptide antibodies recognized petunia COXII but no other
mitochondrial proteins. Anti-URF-S peptide antibodies recognized a
20-kilodalton protein present in both cytoplasmic male sterile and fertile
lines and a protein with an apparent molecular mass of 25 kilodaltons
present only in cytoplasmic male sterile lines. The 25-kilodalton protein
was found to be synthesized by isolated mitochondria and to fractionate
into both the soluble and membrane portions of disrupted mitochondria,
whereas the 20-kilodalton protein was found only in the membrane fraction.
The abundance of the 25-kilodalton protein was much lower in fertile plants
carrying the cytoplasmic male sterile cytoplasm and a single dominant
nuclear fertility restorer gene, Rf. Thus, the pcf gene is correlated with
cytoplasmic male sterility not only by its co-segregation with the
phenotype in somatic hybrids, but also by the modification of its
expression at the protein level through the action of a nuclear gene that
confers fertility.
