Loss of E3 ligaseHvST1function substantially increases recombination

Abstract

AbstractDuring meiosis, genetic recombination occurs via repair of DNA double-strand breaks (DSBs) as crossovers (COs) resulting in the exchange of parental genetic material (1). Crossovers are important for chromosome segregation and shuffling genetic variation, but their number and distribution are tightly regulated (2). In barley and other large genome cereals, recombination events are limited in number and mainly restricted to the ends of chromosomes (3), constraining progress in plant breeding. Recent studies have highlighted subtle differences in meiotic progression (4, 5) and the distribution of recombination events in barley compared to other plants (6-8), indicating possible evolutionary divergence of the meiotic program in large genome crops. Here we identify a spontaneous loss of function mutation in the grass specific E3 ubiquitin ligaseHvST1(Sticky Telomeres 1) which results in semi-sterility in barley. We show that abnormal synapsis in the absence of HvST1 function increases overall recombination by up to 2.5-fold and that HvST1 is capable of ubiquitinating ASY1, a key component of the lateral elements of the synaptonemal complex. Our findings shed light on a novel—and evolutionarily divergent—pathway regulating synapsis and recombination in cereals. This natural loss of function variant presents new opportunities for the modulation of recombination in large genome cereals.Significance StatementClimate change places significant strain on crop production. Crop secondary gene pools offer an excellent resource for crop improvement. However, linkage drag driven by restrictions to meiotic recombination can impose severe yield or quality penalties from introgression of traits from secondary gene pools to elite varieties. Here, we characterize a spontaneous mutation in the barley E3 ubiquitinHvST1that leads to a significant increase in recombination. Through biochemical analysis of the wild type protein we identified a putative role for this ligase in regulating synapsis. This furthers our understanding of the control of synapsis in large genome cereals and may be of direct use in traditional barley breeding.