The RAP2.12 and RAP2.3 factors act downstream of LRR-MAL Receptor Kinases in Arabidopsis pollen-stigma interactions.

Arabidopsis Leucine-Rich Repeat-Malectin Receptor Kinase (LRR-MAL RK) genes have been previously implicated in the early stages of pollen-pistil interactions to support compatible pollen. One member, Receptor Kinase in Flowers 1 (RKF1), has been associated with roles in the stigma to support pollen hydration as well as pollen tube growth. To better understand the function of RKF1 in these processes, a yeast two-hybrid screen was conducted with the RKF1 cytosolic kinase domain. Two positive interactors identified from this screen were the Group VII Ethylene Response Factors (ERFVIIs), RELATED TO APETALA 2.12 (RAP2.12) and RAP2.3. Their putative roles in pollen-pistil interactions were investigated using the quintuple erfvii mutant, and novel pistil-mediated pollen tube callose deposition phenotypes were uncovered during the pollen tube growth stage. Loss of seven LRR-MAL RKs including RKF1 in the pistil was previously found to cause an unusual phenotype where shorter callose plugs were deposited in wildtype pollen tubes compared to that seen in wildtype Col-0 pistils. Contrary to this, wildtype pollen tubes growing through the quintuple erfvii mutant pistil deposited callose plugs that were more elongated than that seen in wildtype Col-0 pistils. Further analyses with the proteolysis 6 (prt6) mutant and RAP2.12 rescue constructs were consistent with these phenotypes providing support that RKF1 is a negative regulator of RAP2.12 and RAP2.3 in the pistil during pollen tube growth.