Below-ground tissues of Capsicum annuum respond to conserved bacterial peptides with pattern-triggered immunity

Plants have an innate immune system that deters and reduces infection by pathogenic microbes. <i>Solanaceous</i> plants such as <i>Solanum lycopersicum</i> (tomato) use cell-surface immune receptors to perceive microbe-associated molecular patterns (MAMPs) and activate pattern-triggered immunity (PTI), but these responses have been seldom explored in roots of other members of the <i>Solanaceae</i> . To investigate the PTI responses in roots of <i>Capsicum annuum</i> (pepper), oxidative luminescence and temporary root growth inhibition assays were used to measure PTI upon treatment with three bacterial MAMPs: two flagellin (flg)-derived peptides (flg22 and flgII-28), and one cold shock protein-derived peptide (csp22), in multiple pepper accessions. Our results show that pepper roots exhibit a significant increase in ROS production in response to csp22, flg22, and flgII-28 treatment, while only flg22 causes temporary root growth inhibition. PTI responses differ in amplitude among MAMPs and genotypes. Together, these results suggest that downstream immune signaling or immune receptor expression may differ among pepper genotypes and MAMP treatments and highlight the importance of investigating immune response variation in various crop plants.