Submitted to: Maize Genetics Conference Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 2/22/1998
Publication Date: N/A
Technical Abstract: Fertility restoration in cmsT maize requires the action of dominant alleles of two unlinked nuclear-restorer loci, rf1 and rf2. Computational analyses of the cloned rf2 gene suggested that it encodes a mitochondrial aldehyde dehydrogenase (mtALDH). Three lines of evidence support this functional assignment. 1) ALDH activity is present in crude extracts of Rf2-expressing E. coli; 2) the rf2 gene can complement an aldh mutant of E coli; and 3) ALDH activity is at least 5-fold lower in mitochondria purified from mutant (rf2/rf2) plants than those from wild-type (Rf2/-) plants. Most maize lines are homozygous for functional Rf2 alleles even though they have never been exposed to the T cytoplasm. To test the hypothesis that the rf2 gene has a physiological role independent of its ability to restore fertility to cmsT maize, a series of rf2-Mu alleles was transferred to an N-cytoplasm version of Ky21. The progeny of this cross were then selfed. In this genetic background all genotypes exerted from th upper floret of each spiklet, functional anthers that shed pollen. However, the anthers from the lower florets of plants homozygous for rf2 alleles (but not their siblings that carried the Rf2-Ky21 allele) aborted late in development. Subsequently, three generations of crosses involving other genetic backgrounds revealed the presence of a variant allele of a previously undescribed nuclear gene, pif1 (partner in fertility), which alters rf2-mediated anther abortion in N-cytoplasm plants. Unless plants that are homozygous for pif1 carry a functional Rf2 allele, they are completely male sterile, i.e., all anthers in both the upper and lower florets abort. Hence, the rf2 gene can play a role in anther development independent of its role as a nuclear restorer of cmsT.