Screening and characterization of apple Rho-like GTPase (MdROPs) genes related to S-RNase mediated self-incompatibility

ROP/Rac GTPase is a conserved class of proteins which play diverse signalling roles in plants. They regulate many fundamental cellular processes such as F-actin dynamics, cell polarity and polar growth. Using apple genomic database analyses, nine ROP family members were cloned for the first time in a fruit tree (apple). Phylogenetic analyses indicated that the nine MdROPs were distributed into two groups, as previously described in the literature for model plants. Expression analyses show all MdROPs were highly expressed in pollen, in particular MdROP1, 3, 4 and 8. Yeast two hybrid and bimolecular fluorescence complementation analyses indicated MdROP8 interacts with S-RNase, a pistil determinate factor in gametophyte self-incompatibility. The pollen tube microtubule is shown to depolymerize in response to S-RNase treatment, during which the expression of MdROP8 rapidly decreased. These results indicate MdROP8 is related to S-RNase mediated self-incompatibility, and gives some useful evidence in modeling the relationship between cytoskeleton depolymerization and pollen tube growth inhibition during the apple SI reaction.