Nuclear expression of a cytoplasmic male sterility gene modifies mitochondrial morphology in yeast and plant cells

ORF138 is the mitochondrion-encoded protein responsible for Ogura cytoplasmic male sterility (cms) in radish (Raphanus sativus) and Brassica sp. As a means of developing technical tools for analyzing the mechanism of cms in relation to the structure of the sterility protein, we generated gene constructs for ORF138, the green fluorescent protein GFP and an ORF138-GFP fusion, to give nuclear expression with mitochondrial targeting of the encoded proteins. These genes were introduced into the yeast Saccharomyces cerevisiae and were transiently and stably expressed in plant cells. The targeting of nuclear-encoded ORF138 protein to the mitochondria did not prevent the growth of yeast cells on fermentable or non-fermentable media, but modified the cytological appearance of mitochondria in both yeast and plant cells. However, the production from a nuclear gene and mitochondrial targeting of ORF138 did not induce male sterility in transgenic A. thaliana plants. This may be due to the submitochondrial location of nuclearly expressed ORF138.