P-346 - Amino acids as molecular signals: Serine and beyond in calcium-mediated immune priming.

Plants activate defense mechanisms through diverse chemical signals, including specialized metabolites, hormones, and small molecules that regulate immune responses. While these chemical inducers have been widely studied, recent evidence suggests that certain amino acids, traditionally known as protein building blocks, also function as signaling molecules in plant immunity. In our study, we found that several amino acids serve as defense activators, with varying degrees of priming effects. Notably, we identified serine as a potent defense activator that primes immune responses through calcium signaling. Serine application activates calcium-permeable channels, leading to the activation of calcium-dependent protein kinases and transcriptional regulators that modulate plant defense pathways. This response promotes the expression of defense genes and enhances the accumulation of the defense hormone salicylic acid (SA), thereby strengthening immune priming. Pre-treatment with serine significantly delays programmed cell death (PCD) during effector-triggered immunity (ETI), likely by reducing pathogen effector activity and consequently decreasing the need for rapid PCD activation compared to water-treated plants. Our findings highlight the emerging role of amino acids as immune modulators and suggest that serine, along with other amino acids and primary metabolites, may serve as a potential tool to enhance crop resilience against pathogens.