Academic journal article Genetics

Mitochondrial DNA Phylogeny of Cultivated and Wild Beets: Relationships among Cytoplasmic Male-Sterility-Inducing and Nonsterilizing Cytoplasms

Academic journal article Genetics

Mitochondrial DNA Phylogeny of Cultivated and Wild Beets: Relationships among Cytoplasmic Male-Sterility-Inducing and Nonsterilizing Cytoplasms

Article excerpt

ABSTRACT

Cytoplasmic male sterility (CMS), the maternally inherited failure to produce functional pollen, has been used in the breeding of sugar beet (Beta vulgaris ssp. vulgaris). At least three different sources of CMS can be distinguished from one another as well as from normal fertile cytoplasm by polymorphisms in their mitochondrial genomes. Here we analyzed 50 accessions of cultivated and wild beets to investigate the phylogenetic relationships among male-sterility-inducing and normal cytoplasms. The haplotypes were characterized by the nucleotide sequence of the mitochondrial cox2-cox1 spacer region and mitochondrial minisatellite loci. The results indicated that (1) a normal cytoplasm line, cv. TK81-O, was situated at the major core node of the haplotype network, and (2) the three sterilizing cytoplasms in question derived independently from the core haplotype. The evolutionary pathway was investigated by physical mapping study of the mitochondrial genome of a wild beet (B. vulgaris ssp. orientalis) accession BGRC56777 which shared the same mitochondrial haplotype with TK81-O, but was not identical to TK81-O for the RFLP profiles of mitochondrial DNA. Interestingly, three sets of inverted repeated sequences appeared to have been involved in a series of recombination events during the course of evolution between the BGRC56777 and the TK81-O mitochondrial genomes.

THE involvement of cytoplasmic factors has been reported in >150 plant species in which male sterility occurs (Laser and Lersten 1972). This type of male sterility, called cytoplasmic male sterility (CMS), is usually attributed to chimeric ORFs in the mitochondrial genome (Chase 2007). In some plant species, multiple forms of CMS are found (Fauron and Casper 1994; Schnable and Wise 1998). These forms can be distinguished by their unusual associated mitochondrial ORFs and by their response to nuclear-encoded, restorer-of-fertility (Rf) genes that suppress the malesterile phenotype.

Several different sources of male-sterile cytoplasms have been described in cultivated beets (Beta vulgaris ssp. vulgaris) and their wild progenitor, all of which are assigned into the section Beta (syn. Vulgares) of the genus Beta (Mikami et al. 1985; Saumitou-Laprade et al. 1993). The first identified was the Owen cytoplasm, discovered in the cultivar "US-1" (Owen 1945). Up to now hybrid seed production in the sugar beet has exclusively relied on Owen CMS (Bosemark 1993). We have recently found that a mitochondrial 35-kDa protein ismost likely responsible for Owen CMS (Satoh et al. 2004; Yamamotoet al. 2005). The protein proved to be the product of a 387-codon mitochondrial ORF (designated preSatp6), which is fused in frame with the downstream atp6 ORF (Yamamotoet al. 2005). Interestingly, this protein was not detectable in the anther tissue of two different sources of CMS ½I-12CMS(2) and I-12CMS (3)] from wild Beta beets collected in Turkey and Pakistan; instead, a CMS-associated protein of 12 kDa was identified (Hallden et al. 1992; M. P. Yamamoto, Y.Onodera,T.KuboandT.Mikami,unpublished results). These three male-sterile cytoplasms showed different patterns of male-sterility maintenance and male-fertility restoration when crossed with the same pollen parents (T. Kubo, T. Kinoshita and T. Mikami, unpublished data). Moreover, Ducos et al. (2001) reported that male sterility caused by the G cytoplasm of wild Beta beets was associated with a mitochondrial cox2 gene lacking eight highly conserved, C-terminal amino acids. Beta beets thus appear to maintain several distinct CMS cytoplasms, each capable of conferring male sterility by an apparently different mechanism.

In this article, we attempted to obtain information on the evolutionary relationships among thesemale-sterilityinducing and nonsterilizing, normal cytoplasms. For this purpose, we determined the nucleotide sequence of the cox2-cox1 intergenic spacer region from a number of cultivated and wild beets as well as CMS accession lines. …

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