Protein ADP-Ribosylation Takes Control in Plant–Bacterium Interactions

Sessile plants detect and ward off invading microorganisms with a robust and sophisticated innate immune system in addition to structural, physical, and chemical barriers [1]. The first line of the plant immune system depends on pattern-recognition receptors (PRRs) that recognize conserved pathogenor microbe-associated molecular patterns (PAMPs or MAMPs) and induce pattern-triggered immunity (PTI) [2]. To counteract this defense, pathogenic microbes have developed various virulence strategies, such as the bacterial type III secretion system (T3SS), through which bacteria inject a battery of effector proteins into plant cells to suppress host immunity and modulate host physiology [3]. Plants have, in turn, evolved intracellular NOD-like receptors (NLRs) that recognize effectors or effector-mediated changes and mount effector-triggered immunity (ETI) [1]. Recent studies show that protein ADP-ribosylation, an important yet less studied posttranslational modification with an emerging role in diverse cellular processes, is exploited both by plants to launch effective defense and by bacteria to achieve stealthy attacks to the hosts. Here, we summarize the classification and biochemical processes of protein ADP-ribosylation, compare the similarities and differences of ADP-ribosylation in plants and animals, and discuss the roles of ADP-ribosylation in plant immunity and bacterial pathogenicity.