Paparo, R. | bioRxiv Science

bioRxiv2024

The mitochondrial orf125 affects male fertility of Solanum tuberosum (+) S. commersonii somatic hybrids and participates in the onset of ''Tuberosum''-Type CMS and evolution of common potato

Cytoplasmic male sterility (CMS) is an agronomically significant trait and a powerful tool to study interactions between nuclear and cytoplasmic genomes. In this study, the chondriomes of two isonuclear male-fertile and sterile somatic hybrids (SH9A and SH9B, respectively) between the common potato (Solanum tuberosum Group Tuberosum, tbr) and the wild species S. commersonii (cmm), were sequenced and compared to those of parental species to identify mitochondrial genes involved in the expression of male sterility. A putative novel gene (orf125) was found only in tbr and in male-sterile hybrids. Two approaches, a physical or functional deletion of orf125 by mtDNA editing in SH9B and its allotopic expression in SH9A, clearly demonstrate that orf125 affects male fertility. To trace the origin of orf125 and hypothesize its role in the evolution of common potato, we searched it in tbr varieties, tuber-bearing potato relatives and other Solanaceae. The organization of the mitochondrial genome region implicated in CMS remained consistent across all common potato accessions in GenBank. An identical tbr copy of orf125 was also detected in all six accessions belonging to the S. berthaultii complex (ber) analyzed. Such findings corroborate the hypothesis that ber accessions with T/{beta} cytoplasm crossed as female with Andean potato (S. tuberosum Group Andigenum, adg), giving rise to the differentiation of the Chilean potato (S. tuberosum Group Chilotanum), and highlights the origin of mitochondrial factors contributing to genic-cytoplasmic male sterility in tbr x adg (or some wild species) hybrids.

plant biology↗

bioRxiv2018

Recombination suppression in heterozygotes for a pericentric inversion induces interchromosomal effect on crossovers in Arabidopsis

During meiosis, recombination ensures the allele exchange through crossovers (COs) between the homologous chromosomes and, additionally, their proper segregation. CO events are under a strict control but molecular mechanisms underlying CO regulation are still elusive. Some advances in this field were made by structural chromosomal rearrangements that are known at heterozygous state to impair COs in various organisms. In this paper, we have investigated the effect that a large pericentric inversion involving chromosome 3 of Arabidopsis thaliana has on male and female recombination. The inversion associated to a T-DNA dependent mutation likely resulted from a side effect of the T-DNA integration. Reciprocal backcross populations, each consisting of over 400 individuals, obtained from the T-DNA mutant and the wild type, both crossed with Landsberg, have been analyzed at genome-wide level by 143 SNPs. We found a strong suppression of COs in the rearranged region in both male and female meiosis. As expected, we did not detect single COs in the inverted region consistently with the post-meiotic selection operating against unbalanced gametes. Cytological analysis of chiasmata in F1 plants confirmed that COs are effectively dropping in chromosome 3 pair. Indeed, CO failure within the inversion is not altogether counterbalanced by CO increase in the regions outside the inversion on chromosome 3. Strikingly, this CO suppression induces a significant increase of COs in chromosome pairs 1, 2 and 5 in male meiosis. We conclude that these chromosomes acquire additional COs thereby compensating the recombination suppression occurring in chromosome 3, similarly to what has been described as interchromosomal (IC) effect in other organisms. In female meiosis, IC effect is not evident. This may be related to the fact that CO number in female is close to the minimum value imposed by the obligatory CO rule.\n\nAuthor SummaryIt is well known that chromosome structure changes in heterozygous condition influence the pattern of meiotic recombination at broad scale. In natural populations, inversions are recognized as the most effective force to reduce COs. In this way, adaptive allele combinations which otherwise would be broken by recombination are maintained. In the present work, we studied the effect on recombination of a large pericentric inversion involving Arabidopsis chromosome 3. The analysis on heterozygous populations provided evidence of strong recombination suppression in chromosome 3. However, the most striking aspect of this study is the finding that the failure of chromosome 3 to recombine is coupled to increased CO frequencies on the other chromosome pairs in male meiosis. These CO compensatory increases are strictly an interchromosomal (IC) effect as was first described in Drosophila. As far as we know, it is the first time IC effect has been reported in plants. Unfortunately, the molecular mechanisms underlying IC effect in the other organisms are still elusive. To understand how a CO change on just one chromosome triggers the global response of the meiocyte to obtain the adequate CO number/cell remains a fascinating question in sexually reproducing species.

genetics↗