The role and regulation of receptor-like kinases in plant defense

Abstract

Receptor-like kinases (RLKs) in plants are a large superfamily of proteins that are structurally similar. RLKs are involved in a diverse array of plant responses including development, growth, hormone perception and the response to pathogens. Current studies have focused attention on plant receptor-like kinases as an important class of sentinels acting in plant defense responses. RLKs have been identified that act in both broad-spectrum, elicitor-initiated defense responses and as dominant resistance (R) genes in race-specific pathogen defense. Most defense-related RLKs are of the leucine-rich repeat (LRR) subclass although new data are highlighting other classes of RLKs as important players in defense responses. As our understanding of RLK structure, activation and signaling has expanded, the role of the ubiquitin/proteasome system in the regulation of these receptors has emerged as a central theme.

Keywords: E3 ligase; disease resistance; elicitors; plant defense; receptor-like kinase; ubiquitin.

Figure 1

The ubiquitin/26S proteasome pathway. The pathway begins with the activation of ubiquitin by ATP and the subsequent linkage via thioester bond to an E1. This is followed by the transfer of ubiquitin to an E2 enzyme. From here the pathway branches, depending on the type of E3 ligase to which the ubiquitin moiety will be transferred. RING/U-box, APC and SCF-type E3 ligases will facilitate the direct transfer of ubiquitin from the E2 to the target substrate. In the case of HECT-domain E3 ligases, the E2 will first transfer the ubiquitin to the HECT-E3 and then the HECT-E3 will transfer the ubiquitin to the target substrate. In both cases, after a chain of multiple ubiquitin moieties is attached to the target substrate it will be recognized by the 26S proteasome and degraded.