The Calcium-Dependent Protein Kinase CPK28 Buffers Plant Immunity and Regulates BIK1 Turnover

Abstract

Plant perception of pathogen-associated molecular patterns (PAMPs) triggers a phosphorylation relay leading to PAMP-triggered immunity (PTI). Despite increasing knowledge of PTI signaling, how immune homeostasis is maintained remains largely unknown. Here we describe a forward-genetic screen to identify loci involved in PTI and characterize the Arabidopsis calcium-dependent protein kinase CPK28 as a negative regulator of immune signaling. Genetic analyses demonstrate that CPK28 attenuates PAMP-triggered immune responses and antibacterial immunity. CPK28 interacts with and phosphorylates the plasma-membrane-associated cytoplasmic kinase BIK1, an important convergent substrate of multiple pattern recognition receptor (PRR) complexes. We find that BIK1 is rate limiting in PTI signaling and that it is continuously turned over to maintain cellular homeostasis. We further show that CPK28 contributes to BIK1 turnover. Our results suggest a negative regulatory mechanism that continually buffers immune signaling by controlling the turnover of this key signaling kinase.

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

“…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). It will be interesting to determine whether PCRK2 regulates its own accumulation by inhibiting its degradation through auto-phosphorylation or phosphorylation of a component required for its degradation.…”

ROS, Calcium, and Electric Signals: Key Mediators of Rapid Systemic Signaling in Plants

“…Indeed, RBOHs are known to be modulated by Ca 2+ -dependent signaling both directly through their EF-hand motifs (Takeda et al, 2008;Kimura et al, 2012) and through posttranslational modulation, such as Ca 2+ -dependent protein kinase activity (e.g. Kimura et al, 2012;Drerup et al, 2013;Dubiella et al, 2013;Li et al, 2014;Monaghan et al, 2014). In such a model where ROS and Ca 2+ interact to propagate a cell-to-cell signal, whether Ca 2+ or ROS lies upstream of the other becomes somewhat of a moot point as the response involves cycles of Ca 2+ -triggered ROS production that are themselves intimately linked to ROSdependent Ca 2+ fluxes (Fig.…”

Phosphorylation of Trihelix Transcriptional Repressor ASR3 by MAP KINASE4 Negatively Regulates Arabidopsis Immunity

“…In addition, PROTEIN PHOSPHATASE 2A regulates the activation of PRR complexes, likely by modulating the phosphorylation status of BAK1 . The calcium-dependent protein kinase CPK28 phosphorylates BIK1 and contributes to BIK1 turnover, thereby negatively regulating PTI signaling (Monaghan et al, 2014).…”