The receptor‐like cytoplasmic kinase PCRK1 contributes to pattern‐triggered immunity against Pseudomonas syringae in Arabidopsis thaliana

Abstract

Summary In this paper we describe PATTERN‐TRIGGERED IMMUNITY (PTI) COMPROMISED RECEPTOR‐LIKE CYTOPLASMIC KINASE 1 (PCRK1) of Arabidopsis thaliana, an RLCK that is important for defense against the pathogen Pseudomonas syringae pv. maculicola ES4326 (Pma ES4326). We examined defense responses such as bacterial growth, production of reactive oxygen species (ROS) and callose deposition in pcrk1 mutant plants to determine the role of PCRK1 during pathogen infection. Expression of PCRK1 was induced following pathogen infection. Pathogen growth was significantly higher in pcrk1 mutant lines than in wild‐type Col‐0. Mutant pcrk1 plants showed reduced pattern‐triggered immunity (PTI) against Pma ES4326 after pretreatment with peptides derived from flagellin (flg22), elongation factor‐Tu (elf18), or an endogenous protein (pep1). Deposition of callose was reduced in pcrk1 plants, indicating a role of PCRK1 in activation of early immune responses. A PCRK1 transgene containing a mutation in a conserved lysine residue important for phosphorylation activity of kinases (K118E) failed to complement a pcrk1 mutant for the Pma ES4326 growth phenotype. Our study shows that PCRK1 plays an important role during PTI and that a conserved lysine residue in the putative kinase domain is important for PCRK1 function.

Two redundant receptor-like cytoplasmic kinases function downstream of pattern recognition receptors to regulate activation of SA biosynthesis in Arabidopsis

“…Similarly, a pcrk1 mutation predicted to abolish its kinase activity also compromises the function of PCRK1 in plant immunity (Sreekanta et al, 2015). These results suggest that the kinase activity of PCRK1 and PCRK2 is critical for their functions, and they probably transduce defense signals through phosphorylation of their protein substrates.…”

“…Interestingly, the K115E mutation in PCRK2 also affects its accumulation in plants through an unknown mechanism. It remains to be determined whether accumulation of the similar mutant in PCRK1 (Sreekanta et al, 2015) is also reduced and whether reduced accumulation of the mutant proteins affects their functions in plant defense. BIK1 protein level was shown to be regulated by proteasome-mediated degradation (Monaghan et al, 2014).…”

“…Since blocking SA biosynthesis leads to enhanced susceptibility to bacterial pathogens (Nawrath and Métraux, 1999), reduced pathogen-induced SA biosynthesis is most likely a major factor contributing to the increased bacterial growth in the pcrk1 pcrk2 double mutant. However, the pcrk1 single mutants were found to exhibit increased disease susceptibility without affecting SA accumulation (Sreekanta et al, 2015), suggesting that PCRK1 also regulates defense responses that are independent of SA.…”

“…Plants lacking both PCRK1 and PCRK2 exhibit enhanced susceptibility to bacterial pathogens. Recently, it was reported that knockout mutants of PCRK1 support higher growth of bacterial pathogens Pma ES4326 and Pto DC3000 as well as the nonpathogenic bacteria Pto DC3000 hrcC 2 (Sreekanta et al, 2015). A double mutant of PCRK1 and PCRK2 was also generated in the study.…”

“…At3g09830 and At5g03320 belong to receptor-like cytoplasmic kinase subfamily VII and share 81% sequence identity. Since At3g09830 was recently designated as PATTERN-TRIGGERED IMMUNITY COMPROMISED RECEPTOR-LIKE CYTOPLASMIC KINASE1 (PCRK1; Sreekanta et al, 2015), we named At5g03320 as PCRK2. To determine the functions of these two kinases, T-DNA insertion mutants for PCRK1 (pcrk1-2, SALK_145629) and PCRK2 (pcrk2-1, SAIL_129_D02) were obtained from the Arabidopsis Biological Resource Center, and the pcrk1-2 pcrk2-1 double mutant (designated as pcrk1 pcrk2) was generated by crossing the two single mutants.…”