Two groups of Arabidopsis receptor kinases preferentially regulate the growth of intraspecies pollen tubes in the female reproductive tract

Abstract

In flowering plants, continuous cell-cell communication between the compatible male pollen 15 grain/growing pollen tube and the female pistil is required for successful sexual reproduction. In 16Arabidopsis thaliana, the later stages of this dialogue are mediated by several peptide ligands 17 and receptor kinases that guide pollen tubes to the ovules for the release of sperm cells. Despite a 18 detailed understanding of these processes, a key gap remains on the nature of the regulators that 19 function at the earlier stages. Here, we report on two groups of A. thaliana receptor kinases, the 20 LRR-VIII-2 RK subclass and the SERKs, that function in the female reproductive tract to regulate 21 the compatible pollen grains and early pollen tube growth, both essential steps for the 22 downstream processes leading to fertilization. Multiple A. thaliana LRR-VIII-2 RK and SERK 23 knockout mutant combinations were created, and several phenotypes were observed such as 24 reduced wild-type pollen hydration and reduced pollen tube travel distances. As these mutant 25 pistils displayed a wild-type morphology, the observed altered responses of the wild-type pollen 26 are proposed to result from the loss of these receptor kinases leading to an impaired pollen-pistil 27 dialogue at these early stages. Furthermore, using pollen from related Brassicaceae species, we 28 also discovered that these receptor kinases are required in the female reproductive tract to 29 establish a reproductive barrier to interspecies pollen. Thus, we propose that the LRR-VIII-2 RKs 30 and the SERKs play a dual role in the preferential selection and promotion of intraspecies pollen 31 over interspecies pollen. 32 33 Key Words: Arabidopsis, receptor kinases, pollen, pistil, compatible intraspecies pollinations, 34 interspecies pollinations 35 is the identification of the key regulators that function in the earlier stages that take place in the 63 stigma/style immediately after pollination. Successful growth of pollen tubes through the A. 64 thaliana stigma/style is a prerequisite to these later stages as pollen tubes growing through the 65 stigma/style then acquire the competency to perceive ovular guidance cues [23]. So far, the only 66 4 putative early stage regulators that have been identified are the pollen-specific genes encoding 67 the Pollen Coat Protein-B (PCP-B) peptides which are required for pollen adhesion and 68 hydration [24]. 69Here, we report that members of two groups of RK genes, the LEUCINE RICH REPEAT (LRR)-70 VIII-2 RKs and the SOMATIC EMBRYOGENESIS RECEPTOR KINASES (SERKs), that are 71 required in the stigma and the female reproductive tract to promote compatible pollen grain 72 hydration and pollen tube growth and to establish a reproductive barrier against interspecies 73 pollen tube growth. The discovery of these RKs was enabled by employing an unconventional 74 approach of using an interspecies tissue-specific pseudokinase as a tool for discovery of 75 candidate RKs by using the assumption that pseudokinases typically associate ...