Crossing-over decision landscape in maize

Abstract

In most crops, including maize, meiotic double-strand breaks (DSBs) occur in all chromosome regions but crossovers (COs) are predominantly near chromosome ends. To understand how the uniform DSB distribution changes into the U-shaped CO distribution, we generated high-resolution maps of CO intermediates. We found that DSBs with medium resection spans more often result in COs than those with shorter or longer resections. We also discovered that sites of CO intermediates associated with MLH3 in zygotene are uniformly distributed along chromosomes, resembling DSB distribution. However, in late prophase, they show the U-shaped distribution characteristic of COs. While zygotene MLH3 sites exhibit methylation levels similar to the genome average, late prophase sites have reduced DNA methylation. In contrast to DNA methylation, inter-parental DNA sequence polymorphism has limited effect on CO distribution. These data indicate that the final CO landscape shape in maize is established late during recombination and controlled by chromatin state.

Exploring impact of recombination landscapes on breeding outcomes

“…If the replacing segment differs in sequence from the original segment, the result of the replacement is a gene conversion (GC). Considering the number of NCOs, the average length of DSB resection, which in maize has been found to be ~1,100 bp ( 14 ), and the level of intraspecies DNA sequence polymorphism, GCs should be a significant contributor to genetic variation in plants. However, detailed analyses of recombination products performed in Arabidopsis failed to produce evidence of substantial GC numbers ( 15 , 16 ).…”