PTPN22 and infection: Paparella et al. (2014) reported that the functional absence of AtLYK3 could affect SA-mediated responses. In addition to chitin recognition, CERK1 and two LysM domain proteins (LYP2, LYP3) are indispensable for peptidoglycan perception and immunity to bacterial pathogen infection (Willmann et al., 2011). Hussan et al. (2020) reported that an LRR-RLK protein LIK1 is involved in Xcc LPS perception, then phosphorylated by CERK1. The above suggests that the recognition of Xcc by the receptors plays an important role in the cabbage’s defense response to Xcc infection.