A Maize (Zea mays L.) BIK1-Like Receptor-Like Cytoplasmic Kinase Contributes to Disease Resistance

Receptor-like cytoplasmic kinases (RLCKs) form a large subfamily of proteins in plants. RLCKs are known to regulate plant immunity to bacterial and fungal pathogens. In this study, we analyzed the genome-wide complement of maize RLCK genes and conducted detailed studies on one maize RLCK. The maize genome encodes 192 RLCKs that largely mirror the RLCK family in other plants. Previous studies implicated Arabidopsis BOTRYTIS INDUCED KINASE1 (BIK1) and TOMATO PROTEIN KINASE 1b (TPK1b) in plant resistance to the bacterial pathogen Pseudomonas syringae and the fungal pathogen Botrytis cinerea. A novel maize RLCK, Zea Mays BIK1-LIKE KINASE 1 (ZmBLK1), was identified based on sequence similarity to the tomato and Arabidopsis RLCKs. We demonstrated that ZmBLK1 displays protein kinase activity in vitro and the protein localizes to the plasma membrane. Importantly, expression of ZmBLK1 partially rescued the growth and disease phenotypes of the Arabidopsis bik1 mutant plants. The expression of ZmBLK1 was induced in maize at 12 h after inoculation with Clavibacter michiganensis subsp. nebraskensis (CMN), the bacterial pathogen causing Goss's wilt. Interestingly, overexpression of ZmBLK1 in transgenic maize increased resistance to CMN but did not impact resistance to Aspergillus ear rot caused by the fungal pathogen Aspergillus flavus and the associated aflatoxin contamination. These findings support our hypothesis that ZmBLK1 contributes to plant resistance to bacterial pathogens likely by modulating events early after pathogen infection, implying that the protein may interact with other membrane proteins early in the immune response pathway.