During meiosis and mitosis, the chromatin is organised stochastically in loop arrays. The formation and stabilisation of chromatin loop arrays is dependent on both cohesin and condensin but independent on the presence of a chromosome axis. The meiotic chromosome axes differ significantly from the mitotic axes. Components of the meiotic chromosome axes are thought to localise on the chromatin during S-phase and G2 in budding yeast and Arabidopsis, respectively, and promote the formation of meiotic DNA double-strand breaks (DSBs). In addition, several evidences suggest that the chromosome axes are required for the repair of SPO11-dependent DSBs off the sister. The status of the meiotic axes may also have an important role in the designation of future crossover sites and crossover interference. However, the composition of the chromosome axes, the regulation of its morphology and its function during meiosis are poorly understood in plants.
The aims of this study consisted at further investigating the function of the axis-associated protein AtASY1 during DSB formation and DSB repair. The interaction between AtASY1 and the structural axis component AtASY3 was tested. In addition, the interplay between chromosome axes and the localisation of the AtSPO11-accessory protein AtPRD3 was analysed. This study showed that the formation of meiotic DSBs is spatially and temporally regulated by the formation of a nascent axis in Arabidopsis. The formation of the axes was independent on the formation of DSBs. However, the repair of DSBs off the sister and the formation of inter-homologue crossovers led to the remodelling of the axes in a pathway dependent on AtPCH2, an AAA ATPase family member. In addition, the phosphorylation level of AtASY1 T295 was increased in response to DSB formation. These highlight the coordination between the formation of DSBs/progression of DSB repair by homologous recombination and the remodelling of the chromosome axes
