Investigating the Role of BRASSIKIN1 (BKN1) in the Compatible Pollen-stigma Interactions in Arabidopsis Species

The basal compatible pollen response pathway in the stigma is initiated upon recognition of compatible pollen. A previous attempt to identify candidate genes in this signal transduction pathway led to the discovery of two tandemly-linked genes that encode pseudokinases, BRASSIKIN1 (BKN1) and BKN2. Interestingly, Arabidopsis thaliana Col-0 is predicted to encode a truncated BKN1, but A. thaliana Hh-0 and Arabidopsis lyrata BKN1 genes encode full length proteins. The A. thaliana bkn2 mutant in the Col-0 accession showed a mild pollen hydration defect when wild-type pollen was placed on the mutant stigmas, and the bkn1-bkn2 double mutant did not show additional defects. To further understand the role of BKN1 in the compatible pollen pathway, BKN1 cDNAs from A. lyrata and A. thaliana Hh-0 were used to complement the bkn1-3 bkn2-5 mutant. Additionally, BKN1 deletions were generated in the A. thaliana Hh-0 accession with the CRISPR/Cas9 system. Results show that BKN1 complementation restored the minor pollen hydration defects when wild-type pollen was placed on stigmas from the complementation lines, and no significant fertility defect was seen in A. thaliana Hh-0 bkn1 mutants, both results suggesting the functional redundancy between BKN1 and BKN2.M.Sc