Cytoplasmic male sterility in beta is associated with structural rearrangements of the mitochondrial DNA and is not due to interspecific organelle transfer

Cytoplasmic male sterility (CMS) in Lolium perenne L.: 1. Development of a diagnostic probe for the male-sterile cytoplasm

Analysis of reciprocal crosses between nonrestoring fertile genotypes and restored male-sterile genotypes of Lolium perenne confirmed the cytoplasmic nature of the sterility trait. This prompted a search for a molecular probe that could be used to distinguish between fertile and cytoplasmic male-sterile (CMS) cytoplasms. We describe the identification and cloning of a 4.5-kb BamHI-HindIII restriction fragment from the mtDNA of the CMS line. The cloned fragment (pCMS45) failed to hybridise to sequences in the mtDNA of fertile lines and was thus capable of unambiguously distinguishing between fertile and CMS cytoplasms. The use of pCMS45 as a diagnostic probe provided a simple test for positive identification of young non-flowering plants carrying the CMS cytoplasm and also permitted confirmation at the molecular level of the maternal transmission of the CMS trait suggested by the genetic data.

Variation in mitochondrial translation products in fertile and cytoplasmic male-sterile sugar beets

Intact and functional mitochondria were isolated from sugar beet plants (Beta vulgaris L.) containing normal fertile (F) or cytoplasmic male-sterile (S1-S4) cytoplasms. Incorporation of (35)S-methionine by mitochondria isolated from both roots and leaves showed approximately 20 major and ten minor translation products. Comparison of the polypeptide synthesis patterns produced by leaf mitochondria from fertile plants of three different species within the genus Beta revealed several taxonomically related differences. Contrary to this, the patterns of polypeptides synthesized by mitochondria from roots and leaves of sugar beet plants containing the F and S1-S4 cytoplasms were very similar; in the S1 and S2 cytoplasms no qualitative, and only a few quantitative, differences from the F cytoplasm were observed. Thus, in these cases, cytoplasmic male sterility in sugar beet is not correlated with the constitutive expression of variant polypeptides. In the S3 cytoplasm, however, an additional 6 kDa polypeptide was synthesized and in the S4 cytoplasm an additional 10 kDa polypeptide was observed when compared with the F cytoplasm. The expression of cytoplasmic male sterility in sugar beet may be associated with these variant polypeptides. The mitochondrial polypeptides synthesized were identical in plants with different nuclear backgrounds but with identical S1 cytoplasms. Mitochondria from plants with variants of the S4 cytoplasm in the same nuclear genotype also showed identical patterns of polypeptide synthesis, including the synthesis of the 10 kDa S4-specific polypeptide. Pulse-chase experiments did not affect the synthesis of this polypeptide.