The NbCBP1-NbSAMS1 Module Promotes Ethylene Accumulation to Enhance Nicotiana benthamiana Resistance to Phytophthora parasitica Under High Potassium Status

Potassium (K) fertilization is crucial for plant resistance to pathogens, but the underlying mechanisms remain unclear. Here, we investigate the molecular mechanism by which the addition of K promotes resistance in <i>Nicotiana benthamiana</i> to <i>Phytophthora parasitica</i>. We found that <i>N. benthamiana</i> with high K content (HK, 52.3 g/kg) produced more ethylene in response to <i>P. parasitica</i> infection, compared to <i>N. benthamiana</i> with low-K content (LK, 22.4 g/kg). An exogenous ethylene application effectively increased resistance in LK <i>N. benthamiana</i> to the level under HK status, demonstrating the involvement of ethylene in the HK-associated resistance in <i>N. benthamiana</i>. Further, transcriptome analysis showed that <i>NbSAMS1</i>, encoding ethylene biosynthesis, was induced to upregulate <i>P. parasitica</i> about five times higher in HK than in LK <i>N. benthamiana. NbSAMS1</i> overexpression enhanced resistance in LK plants, whereas <i>NbSAMS1</i> silencing reduced resistance in HK plants, confirming its importance in conferring resistance. Furthermore, we identified a calcium-binding protein, NbCBP1, which interacted with NbSAMS1, promoting its expression in HK <i>N. benthamiana.</i> Silencing <i>NbCBP1</i> compromised resistance in HK <i>N. benthamiana</i>, whereas its overexpression improved resistance in LK <i>N. benthamiana</i>. Notably, NbCBP1 protected NbSAMS1 from degradation by the 26S proteasome, thereby sustaining ethylene accumulation in HK <i>N. benthamiana</i> in response to <i>P. parasitica</i> infection. Thus, our research elucidated some mechanisms of the NbCBP1-NbSAMS1 module associated with disease resistance in HK <i>N. benthamiana.</i>