The dynamic association of SPO11-1 with conformational changes of meiotic axial elements in maize

Double strand breaks (DSBs) are generated at the beginning of meiosis by the evolutionarily conserved SPO11 complex that targets preferentially open chromatin. However, how DSBs are formed with respect to chromosome axes in a timely controlled manner remain unclear. Here, we analyzed the maize spo11-1 mutant and show that it strongly impairs DSB and bivalent formations. Notably, cytological characterization in the spo11-1 mutant revealed abnormally twisted axial elements that persisted until pachytene. In contrast, examinations of precisely staged wild-type meiocytes uncovered a transient remodeling of axial elements, changing from a curly to linear morphology during leptotene to zygotene transition, which is coincident with DSB formation. Using a SPO11-1 antibody, approximately 300 foci were detected from leptotene to pachytene in wild-type meiocytes. Interestingly, when examining distances between SPO11-1 foci to chromosome axes by super-resolution microscopy, predominant loading of SPO11-1 onto axial elements occurs concordantly with alteration of axial elements during leptotene. Taken together, our results suggest a dynamic localization of SPO11-1 during early meiosis that is correlated with a remodeling of the axial element conformation.