ABC transporter PEN 3/ PDR 8/ ABCG 36 interacts with calmodulin that, like PEN 3, is required for Arabidopsis nonhost resistance

Nonhost resistance ( NHR ) is the most prevalent form of plant immunity. In Arabidopsis, NHR requires membrane‐localized ATP ‐binding cassette ( ABC ) transporter PENETRATION ( PEN ) 3. Upon perception of pathogen‐associated molecular patterns, PEN 3 becomes phosphorylated, suggestive of PEN 3 regulation by post‐translational modification. Here, we investigated the PEN 3 protein interaction network. We probed the Arabidopsis protein microarray At PMA ‐5000 with the N‐terminal cytoplasmic domain of PEN 3. Several of the proteins identified to interact with PEN 3 in vitro represent cellular Ca 2+ sensors, including calmodulin (CaM) 3, CaM7 and several CaM‐like proteins, pointing to the importance of Ca 2+ sensing to PEN 3‐mediated NHR . We demonstrated co‐localization of PEN 3 and CaM7, and we confirmed PEN 3–CaM interaction in vitro and in vivo by PEN 3 pull‐down with CaM Sepharose, CaM overlay assay and bimolecular fluorescence complementation. We also show that just like in pen3, NHR to the nonadapted fungal pathogens Phakopsora pachyrhizi and Blumeria graminis f.sp. hordei is compromised in the Arabidopsis cam7 and pen3 cam7 mutants. Our study discloses CaM7 as a PEN 3‐interacting protein crucial to Arabidopsis NHR and emphasizes the importance of Ca 2+ sensing to plant immunity.