The maintenance of genome integrity over cell divisions is critical for plant development and the correct transmission of genetic information to the progeny. A key factor involved in this process is the STRUCTURAL MAINTENANCE OF CHROMOSOME5 (SMC5) and SMC6 (SMC5/6) complex, related to the cohesin and condensin complexes that control sister chromatid alignment and chromosome condensation, respectively. Here, we characterize NON-SMC ELEMENT4 (NSE4) paralogs of the SMC5/6 complex in Arabidopsis (Arabidopsis thaliana). NSE4A is expressed in meristems and accumulates during DNA damage repair. Partial loss-of-function nse4a mutants are viable but hypersensitive to DNA damage induced by zebularine. In addition, nse4a mutants produce abnormal seeds, with noncellularized endosperm and embryos that maximally develop to the heart or torpedo stage. This phenotype resembles the defects in cohesin and condensin mutants and suggests a role for all three SMC complexes in differentiation during seed development. By contrast, NSE4B is expressed in only a few cell types, and loss-of-function mutants do not have any obvious abnormal phenotype. In summary, our study shows that the NSE4A subunit of the SMC5-SMC6 complex is essential for DNA damage repair in somatic tissues and plays a role in plant reproduction.
Although gene duplications provide genetic backup and allow genomic changes under relaxed selection, they may potentially limit gene flow. When different copies of a duplicated gene are pseudo-functionalized in different genotypes, genetic incompatibilities can arise in their hybrid offspring. While such cases have been reported after manual crosses, it remains unclear whether they occur in nature and how they affect natural populations. Here we identified four duplicated-gene based incompatibilities including one previously not reported within an artificial Arabidopsis intercross population. Unexpectedly, however, for each of the genetic incompatibilities we also identified the incompatible alleles in natural populations based on the genomes of 1,135 Arabidopsis accessions published by the 1001 Genomes Project. Using the presence of incompatible allele combinations as phenotypes for GWAS, we mapped genomic regions that included additional gene copies which likely rescue the genetic incompatibility. Reconstructing the geographic origins and evolutionary trajectories of the individual alleles suggested that incompatible alleles frequently co-exist, even in geographically closed regions, and that their effects can be overcome by additional gene copies collectively shaping the evolutionary dynamics of duplicated genes during population history.
The fate of duplicated genes includes pseudo-, sub-, or neo-functionalization. When different copies of a duplicated gene are pseudo-functionalized in different genotypes, genetic incompatibilities can arise in their hybrid offspring. While such cases have been reported after manual crosses, it remains unclear whether they occur in nature and how they affect natural populations. Using the Arabidopsis multi-parental RIL population, we identified four duplicated-gene based incompatibilities including one previously not reported. Unexpectedly, however, for each of the genetic incompatibilities we found incompatible allele combinations in natural Arabidopsis accessions. Using the incompatible allele combinations as phenotypes for GWAS, we mapped genomic regions containing additional gene copies, which rescue the incompatible allele combinations. Reconstructing the geographic origins of the individual alleles suggested that incompatible alleles co-exist in nature, and that their effects can be overcome by additional gene copies collectively shaping the evolutionary dynamics of duplicated genes during population history.
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