RFLP ANALYSIS OF MITOCHONDRIAL-DNA FROM CYTOPLASMIC MALE-STERILE LINES OF PEARL-MILLET

Mitochondrial DNA (mtDNA) from 13 cytoplasmic male-sterile (cms) lines from diverse sources were characterized by Southern blot hybridizatio n to pearl millet and maize mtDNA probes. Hybridization patterns of mt DNA digested with PstI, BamHI, SmaI or XhoI and probed with 13.6-, 10. 9-, 9.7- or 4.7-kb pearl millet mtDNA clones revealed similarities amo ng the ems lines 5141 A and ICMA 1 (classified as the S-A1 type of cyt oplasm based on fertility restoration patterns), PMC 30A and ICMA 2. T he remaining ems lines formed a distinct group, within which three sub groups were evident. Among the maize mitochondiral gene clones used, t he coxI probe revealed two distinct groups of cytoplasms similar to th e pearl millet mtDNA clones. The atp9 probe differentiated the ems lin e 81 A4, derived from P. glaucum subsp. monodii, while the coxII gene probe did not detect any polymorphism among the ems lines studied. MtD NA digested with BamHI, PstI or XhoI and hybridized to the atp6 probe revealed distinct differences among the ems lines. The maize atp6 gene clone identified four distinct cytoplasmic groups and four subgroups within a main group. The mtDNA fragments hybridized to the atp6 gene p robe with differing intensities, suggesting the presence of more than one copy of the gene in different stoichiometries. Rearrangements invo lving the coxI and/or rrn18-rrn5 genes (mapped within the pearl millet clones) probably resulted in the S-A1 type of sterility. Rearrangemen ts involving the atp6 gene (probably resulting in chimeric form) may b e responsible for male sterility in other ems lines of pearl millet.