A Mitochondrial DNA Sequence Is Associated with Abnormal Pollen Development in Cytoplasmic Male Sterile Bean Plants

Abstract

Cytoplasmic male sterility (CMS) in common bean is associated with the presence of a 3-kb unique mitochondrial sequence designated pvs. The pvs sequence encodes at least two open reading frames (297 and 720 bp in length) with portions derived from the chloroplast genome. Fertility restoration by the nuclear restorer gene Fr results in the loss of this transcriptionally active unique region. We examined the effect of CMS (pvs present) and fertility restoration by Fr (pvs absent) on the pattern of pollen development in bean. In the CMS line, pollen aborted in the tetrad stage late in microgametogenesis. Microspores maintained cytoplasmic connections throughout pollen development, indicating aberrant or incomplete cytokinesis. Pollen-specific events associated with pollen abortion and fertility restoration imply that a gametophytic factor or event may be involved in CMS. In situ hybridization experiments suggested that significant reduction or complete loss of the mitochondrial sterility-associated sequence occurred in fertile pollen of F2 populations segregating for fertility. These observations support a model of fertility restoration by the loss of a mitochondrial DNA sequence prior to or during microsporogenesis/gametogenesis.

Alloplasmic male-sterile Brassica lines containing B. tournefortii mitochondria express an ORF 3? of the atp6 gene and a 32 kDa protein

“…Differences in transcription patterns between B. tournefortii and the alloplasmic lines were found with two of the geneand ORF-specific clones given in Table 1 and with some of the genomic PstI, SalI and KpnI clones of B. campestris. Studies of mitochondrial transcriptional changes found between sterile and restored CMS lines have shown that such changes were caused by nuclear-induced alterations of the genomic organization [28] or by nuclear influence on transcription and/or post-transcriptional processes [1,26,27,44,52]. The RNA difference found for the atp6 gene in the present study reflected most likely a nuclear influence on transcription and/or RNA processing level, since the Southern analysis revealed no genomic differences between B. tournefortii and the alloplasmic lines in the atp6 region.…”

“…Investigations of several CMS cytoplasms have shown that male sterility is associated with alterations of the mitochondrial genome [reviewed by 10,22,40]. In maize, Petunia sunflower and bean, CMS-associated mitochondrial DNA (mtDNA) rearrangements have generated novel open reading frames (ORFs) [ 11,16,28,33,36,57]. These ORFs, which show no overall homoThe nucleotide sequence data reported will appear in the EMBL, GenBank and DDBJ Nucleotide Sequence Databases under the accession number X83692.…”

A cytoplasmic male sterility-associated mitochondrial protein causes pollen disruption in transgenic tobacco.

“…The association of CMS with abnormal mitochondrial gene expression has been established in many plant species including maize (1,2), petunia (3,4), sunflower (5)(6)(7)(8), and common bean (9,10). In all cases, pollen disruption in CMS lines is accompanied by the expression of novel mitochondrial DNA sequences that contain protein-coding open reading frames.…”

“…In CMS common bean, male-sterile plants contain a novel mitochondrial DNA sequence (designated pvs) of unknown origin that is associated with the pollen sterility phenotype by various genetic criteria (10,11). The 3.7-kb pvs sequence contains at least two open reading frames, ocf239 and orf98.…”

“…We assume that the ORF239 product alone, without a mitochondrial transit sequence, is not capable of targeting to the mitochondrion. The NH2 terminus of ORF239 does not contain the common features of a mitochondrial transit sequence; instead of a basic sequence, the putative helix-forming regions contain many acidic residues that do not appear amphiphilic (10). The two promoters, Psp and PLat52, were used to direct the expression of orf239 gene fusions in developing microspores.…”