A Multiprotein Complex Regulates Interference-sensitive Crossover Formation in Rice

In most eukaryotes, a set of conserved proteins that are collectively termed ZMM proteins (named after ZIP1/2/3/4, MSH4/5, MER3, and SPO16 in Saccharomyces cerevisiae) are essential for the formation of the majority of meiotic crossovers (COs). Recent reports indicated that ZIP2 acts together with SPO16 and ZIP4 to control CO formation through recognizing and stabilizing early recombination intermediates in budding yeast. However, whether this mechanism is conserved in plants is not clear. Here, we characterized the functions of OsSHOC1 (ZIP2 ortholog), OsPTD (SPO16 ortholog) and their interactions with other ZMM proteins in rice (Oryza sativa). We demonstrated that disruption of OsSHOC1 caused a reduction of CO numbers to ~ 83% of wild type, whereas synapsis and early meiotic recombination steps were not affected. Furthermore, OsSHOC1 interacts with OsPTD, which is responsible for the same set of CO formations as OsSHOC1. Additionally, OsSHOC1 and OsPTD are required for the normal loading of other ZMM proteins, and conversely, the localizations of OsSHOC1 and OsPTD were also affected by the absence of OsZIP4 and OsHEI10. OsSHOC1 interacts with OsZIP4, OsMSH5 ,and PTD interacts with OsHEI10. Furthermore, BiFC and yeast-three hybrid assays demonstrated that OsSHOC1, OsPTD, OsHEI10, and OsZIP4 were able to form various combinations of heterotrimers. Moreover, statistical and genetic analysis indicated that osshoc1-2 and osptd-1 are epistatic to oshei10 and oszip4 in meiotic CO formation. Taken together, we propose that OsSHOC1, OsPTD, OsHEI10, and OsZIP4 form multiple protein complexes that have conserved functions in promoting class I CO formation.