SMC5/6 Complex Subunit NSE4A is Involved in DNA Damage Repair and Seed Development in Arabidopsis.

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 MAINTAINANCE OF CHROMOSOME 5/6 (SMC5/6) complex, related to 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. 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 non-cellularized endosperm and embryos that maximally develop to the heart or torpedo stage. This resembles defects in cohesin and condensin mutants and suggests a role for all three SMC complexes in differentiation during seed development. In contrast, NSE4B is expressed only in a few cell types and loss-of-function mutants do not have any obvious phenotype. In summary, our study shows that the NSE4A subunit of the SMC5/6 complex is essential for DNA damage repair in somatic tissues, and plays a role in plant reproduction.