Changes in planta K nutrient content altered the interaction pattern between Nicotiana benthamiana and Alternaria longipes.

Potassium (K) fertilisation has frequently been shown to enhance plant resistance against pathogens, though the mechanisms remain elusive. This study investigates the interaction dynamics between Nicotiana benthamiana and the pathogen Alternaria longipes under different planta K levels. On the host side, adding K activated the expressions of three NLR (nucleotide‐binding domain and leucine‐rich repeat‐containing proteins) resistance genes, including NbRPM1, NbR1B23 and NbNBS12. Silencing these NLRs attenuated resistance in high‐K (HK, 40.8 g/kg) plant, whereas their overexpression strengthened resistance in low‐K (LK, 23.9 g/kg) plant. Typically, these NLRs mainly strengthened plant resistance via promoting the expression of pathogenesis‐related genes (PRs), ROS burst and synthesis of antifungal metabolites in HK plant. On the pathogen side, the expression of effectors HKCSP1, HKCSP2 and LKCSP were shown to be related to planta K content. A. longipes mainly expressed effectors HKCSP1 and HKCSP2 in HK plant to interfere host resistance. HKCSP1 physically interacted with NbRPM1 to promote the degradation of NbRPM1, then attenuated related resistance in HK N. benthamiana. Meanwhile, HKCSP2 directly interacted with NbPR5 to suppress resistance in HK plant. In LK plant, A. longipes mainly deployed LKCSP that interacted with NbR1B23 to interfere reduce resistance in N. benthamiana. Overall, our research insights that both pathogen and host mobilise distinct strategies to outcompete each other during interactions in different K nutrient environments. Summary statement: The present study demonstrated that changes in planta K content could mediate the interaction pattern between host plants and pathogens, eventually leading different outcome of plant disease. Although the pathogen tries to suppress host immune by deploying different virulence factors, the host can benefit much more due to its sufficient resistance events under high K condition. Our results add to evidence that K fertilisation can be adjusted to optimise suppression of fungal diseases and thus has value as a disease management tool. [ABSTRACT FROM AUTHOR]