Identification of New Regulators of the Pollen-pistil Dalogue in Arabidopsis thaliana

In flowering plants, continuous cell-to-cell communication between the male pollen grain/growing pollen tube and the female pistil is required for successful sexual reproduction. In Arabidopsis thaliana, the later stages of this dialogue are mediated by several peptide ligands and receptor kinases that guide pollen tubes to the ovules for the release of sperm cells. Despite a detailed understanding of these processes, a key gap remains on the nature of the regulators that function at the earlier stages. This thesis describes the identification and characterization of two groups of A. thaliana receptor-like kinases, the LRR-VIII-2 RLK subgroup and the SERKs, that are implicated in this process. These receptor-like kinases were observed to function in the female reproductive tract to regulate the compatible pollen grains and early pollen tube growth, both essential steps for the downstream processes leading to fertilization. Multiple A. thaliana LRR-VIII-2 RLK and SERK knockout mutant combinations were created, and several phenotypes were observed such as reduced wild-type pollen hydration and reduced pollen tube travel distances. As these mutant pistils displayed a wild-type morphology, the observed altered responses of the wild-type pollen are proposed to result from the loss of these receptor-like kinases leading to an impaired pollen-pistil dialogue at these early stages. Furthermore, using pollen from related Brassicaceae species, we also discovered that these receptor-like kinases are required in the female reproductive tract to establish a reproductive barrier to interspecies pollen. Thus, we propose that the LRR-VIII-2 RLKs and the SERKs play a dual role in the preferential selection and promotion of intraspecies pollen over interspecific pollen.Ph.D