Variations in the structure and transcription of the mitochondrial atp and cox genes in wild Solanum species that induce male sterility in eggplant (S. melongena)

Abstract

In order to determine the molecular basis of cytoplasmic male sterility (CMS) in alloplasmic lines of eggplant, the genomic structures and transcription patterns of mitochondrial ATP synthase subunit (atp) and cytochrome oxidase subunit (cox) genes were studied for wild and cultivated eggplants. Alloplasmic eggplant lines with cytoplasms of wild Solanum species showing either anther indehiscent type of CMS or non-pollen production type of CMS were studied with the cultivated eggplant Solanum melongena, used as a control. Southern hybridization of the mitochondrial genes indicated the difference between the two types of CMS and showed complete identity within each type. The cytoplasmic patterns of all wild species differed from that of the cultivated eggplant. Thus, the cytoplasm of the six wild eggplants and the one cultivated eggplant was classified into three groups. Male sterile plants of both types of CMS showed novel transcription patterns of atp1, whereas a different transcription pattern of cox2 was observed only in the anther indehiscent type. Based on these differences, we determined the DNA sequences of about a 4 kbp segment in the atp1 region. Although the coding and 3' flanking regions were almost identical among the cytoplasms, the 5' flanking region was completely different and novel open reading frames (orfs) were found for each of the CMS types and the cultivated eggplant. The cytoplasm of Solanum kurzii inducing the anther indehiscent type CMS had orf312, and those of Solanum aethiopicum and Solanum grandifolium of non-pollen production type CMS had orf218. The correspondence between the transcription patterns of these orfs and phenotypic expression of male sterility strongly suggests that these orfs are causal genes for each type of CMS.

Cell-to-cell movement of mitochondria in plants

“…We therefore believe that CMS is not caused by atp1 coding sequence SNPs in our experimental system. The predicted ORF293 protein is similar to the predicted protein product of mitochondrial ORF312 present in the alloplasmic CMS eggplant (Solanum melongena, carrying the cytoplasm of S. kurzii) (GenBank AB762696) (30) and to sequences in the pepper mitochondrial genomes, where the sequences are split (GenBank KJ865410; KJ865409). The region of N. undulata mitochondrial genome carrying orf293 is rearranged relative to the N. sylvestris mitochondrial genome.…”

Development and Fertility Restoration of CMS Eggplant Lines Carrying the Cytoplasm of Solanum violaceum

“…The CMS phenotype in alloplasmic eggplant was associated with the transcription patterns of novel open reading frames (ORFs) in the 5' flanking region of atp1 mitochondrial gene (Yoshimi et al, 2013). In the present study the negative effect of the S. violaceum cytoplasm on male fertility of the MS plants was expressed with reduced pollen release ability, abnormalities in anther morphology and low pollen viability (Figure 2b, Tables 2-4).…”

“…In the abovementioned CMS systems, the fertility restored plants exhibited marked differences in the procession of the co-transcripts of a novel orf and atp1 in relation to the CMS counterparts (Yoshimi et al, 2013). However, the presence of the Rf-genes was not confirmed in the pollen non-releasing (functional) CMS eggplant lines carrying the cytoplasms of S. violaceum, S. virgianum and S. kurzii (Isshiki & Kawajiri, 2002;Khan & Isshiki, 2009.…”

“…For example, plant BC 1 (V×E) 9b was initially characterized as MF due to pollen release ability throughout the observation period, but the respective backcrossing segregation ratio suggested that it was probably a PMF one (Table 2; cross 11). In addition, it cannot be ruled out that some alleles involved in the fertility restoration were lost during the backcrossing process due to the minor effect on the fertility phenotype, relative small population size, environmental effects on phenotypic expression of the fertility (Duvick, 1956;Yoshimi et al, 2013) or linkage with the dwarf or chlorotic phenotypes mentioned in the results section. Nevertheless, further experiments should be pursued in order to incorporate the Rf-genes in the genetic backgrounds of cvs.…”

Cytoplasmic Male Sterility in Eggplant

“…Isolation and studies of the function of the Rf gene might allow a better understanding of the mechanisms involved. The molecular basis of CMS in alloplasmic lines of eggplant was reported where genomic structures and transcription patterns of mitochondrial ATP synthase subunit and cytochrome oxidase subunit genes were studied for wild and cultivated eggplants (Yoshimi et al, 2013). Diversification of CMS sources is needed for use in commercial hybrid seed production.…”