Discrepant involvement of homologous repair and non-homologous end joining pathways in maize development and growth

Chromosomal DNA double-strand breaks (DSBs) are produced in the genome of all living organisms. To combat DNA damage, organisms have evolved several DSB repair mechanisms, of which nonhomologous end-joining (NHEJ) and homologous recombination (HR) represent the two most prominent. Although two major pathways have been studied extensively in Arabidopsis, rice and other mammals, the mechanisms that influence the choice between competing DSB repair pathways are less well understood. Here, we characterized mre11a and rad50, the mutants of HR pathway patterns, in which the typically persistent embryo and endosperm were drastically degraded during kernel development. Loss of MRE11 or RAD50 function caused chromosomal fragments and chromosomal bridges in anaphase. While, we also reported that the NHEJ pathway patterns, KU70 and KU80 are associated with developmental growth and genome stability. ku70 and ku80 both display an obvious dwarf phenotype. Cytological analysis of the mutants revealed extensive chromosome fragmentation in metaphase and subsequent stages. The loss of KU70/80 function upregulated the expression of genes involved in cell cycle progression and nuclear division. These results indicated how NHEJ and HR are executed mechanistically in different plant developmental periods, and may provide valuable information for a competitive and complementary relationship between the NHEJ and HR pathways for DNA double-strand break repair in maize.