Accurate segregation of chromosomes at the first meiotic division relies upon the establishment of physical connections between homologous chromosomes, which with a few exceptions, are realized by crossover recombination. Recombination also reshuffles genetic information between homologs, and thus strongly influences genome evolution. At the molecular level, meiotic recombination is initiated by the programmed induction of DNA double strand breaks (DSBs) and their subsequent repair as a crossover (CO) or a non-crossover (NCO). However, COs are constrained and the majority of DSBs are repaired as NCOs in plants. Gutierrez Pinzon et al. provide a comprehensive overview of the most recent findings on the different steps controlling meiotic recombination, with an emphasis on the different anti-CO pathways. Notably, one of these, involving the RecQ4 helicase, has previously been shown to be active in Arabidopsis, rice, pea and tomato (Séguéla-Arnaud et al., 2015; Mieulet et al., 2018). Arrieta et al. extend this anti-CO role to the cereal barley. Through a suppressor screen of a CO-defective mutant, they show that mutating the RecQ4 gene in Barley can increase meiotic recombination by nearly two-fold. The RecQ4 anti-CO pathway, initially discovered in Arabidopsis, appears thus largely conserved and translatable to cereals. Mechanisms of meiotic recombination are thus largely conserved across plant kingdom. Nevertheless specificities exist, as nicely illustrated by the characterization of the maize checkpoint clamp loader RAD17 by Zhang et al. RAD17 is not essential for meiotic DSB repair in Arabidopsis, while rice Osrad17 mutants exhibit extensive meiotic chromosome fragmentation leading to male and female sterility (Hu et al., 2018). Here, Zhang et al., demonstrate that RAD17 is also essential for meiotic DSB repair in maize but, remarkably and contrary to rice, only in male meiosis. Thus, besides underlining the importance of studying various plant species, this work also points to important differences between male and female meiosis (highlighted by Gutierrez Pinzon et al.). New issues have also recently emerged at the forefront of research on meiotic recombination. First, considering the impact of global warming, understanding how temperature affects meiosis has become a major challenge and recent breakthroughs have been comprehensively described by Gutierrez Pinzon et al. Second, Dziegielewski and Ziolkowski present an extensive review of the knowledge around non-coding RNAs (ncRNAs) and their impact on plant meiosis. NcRNAs are key players in many biological processes, but their role in meiosis has remained elusive. An interesting proposal of Dziegielewski and Ziolkowski is that ncRNA pathways regulate meiosis through the controlled expression of meiosis-specific genes and this role may have evolved as a secondary effect of their primary function in the control of transposable elements in germ cells.
