The molecular signatures of compatible and incompatible pollination

16 Fertilization in flowering plants depends on the early contact and recognition of pollen grains by 17 the receptive papilla cells of the stigma. To identify the associated molecular pathways, we 18 developed a transcriptomic analysis based on single nucleotide polymorphisms (SNPs) present in 19 two Arabidopsis thaliana accessions, one used as female and the other as male. We succeeded in 20 distinguishing 80 % of transcripts according to their parental origins and drew up a catalog of genes 21 whose expression is modified after pollen-stigma interaction. Global analysis of our data reveals 22 that pattern-triggered immunity (PTI)-associated transcripts are upregulated after compatible 23 pollination. From our analysis, we predicted the activation of the Mitogen-activated Protein Kinase 24 3 on the female side after compatible pollination, which we confirmed through expression and 25 mutant analysis. Our work defines the molecular signatures of compatible and incompatible 26 pollination, highlights the active status of incompatible stigmas, and unravels a new MPK3-27 dependent cell wall feature associated with stigma-pollen interaction