An SMC-like protein is required for efficient homologous recombination in Arabidopsis

In plants, the observed low frequency of gene targeting and intrachromosoma l recombination contrasts markedly with the efficient extrachromosomal reco mbination of DNA. Thus, chromatin accessibility can have a major influence on the recombination frequency of chromosomal DNA in vivo. An Arabidopsis m utant hypersensitive to a range of DNA-damaging treatments (UV-C, X-rays, m ethyl methanesulfonate and mitomycin C) is also defective in somatic intrac hromosomal homologous recombination, The wild-type gene encodes a protein c losely related to the structural maintenance of chromosomes (SMC) family in volved in structural changes in chromosomes. Although loss of SMC function is lethal in other eukaryotes, growth of the Arabidopsis mutant is normal i n the absence of genotoxic treatments. This suggests a surprisingly special ized function for this protein in plants, and provides the first in vivo ev idence for the involvement of an SMC protein in recombinational DNA repair. It is possible that SMC-like proteins in plants alleviate suppressive chro matin structure limiting homologous recombination in somatic cells.