A novel LRR receptor-like kinase BRAK reciprocally phosphorylates PSKR1 to enhance growth and defense in tomato

Abstract Plants face constant threats from pathogens, leading to growth retardation and crop failure. Cell-surface leucine-rich repeat receptor-like kinases (LRR-RLKs) are crucial for plant growth and defense, but their specific functions, especially to necrotrophic fungal pathogens, are largely unknown. Here, we identified an LRR-RLK (Solyc06g069650) in tomato ( Solanum lycopersicum ) induced by the economically important necrotrophic pathogen Botrytis cinerea . Knocking out this LRR-RLK reduced plant growth and increased sensitivity to B. cinerea , while its overexpression led to enhanced growth, yield, and resistance. We named this LRR-RLK as BRAK ( B . cinerea resistance-associated kinase). Yeast two-hybrid screen revealed BRAK interacted with phytosulfokine (PSK) receptor PSKR1. PSK-induced growth and defense responses were impaired in pskr1 , brak single and double mutants, as well as in PSKR1 -overexpressing plants with silenced BRAK . Moreover, BRAK and PSKR1 phosphorylated each other, promoting their interaction as detected by microscale thermophoresis. This reciprocal phosphorylation was crucial for growth and resistance. In summary, we identified BRAK as a novel regulator of seedling growth, fruit yield and defense, offering new possibilities for developing fungal disease-tolerant plants without compromising yield.