A Cysteine-Rich Protein Kinase Associates with a Membrane Immune Complex and the Cysteine Residues Are Required for Cell Death

Abstract

Membrane-localized proteins perceive and respond to biotic and abiotic stresses. We performed quantitative proteomics on plasma membrane-enriched samples from Arabidopsis (Arabidopsis thaliana) treated with bacterial flagellin. We identified multiple receptor-like protein kinases changing in abundance, including cysteine (Cys)-rich receptor-like kinases (CRKs) that are up-regulated upon the perception of flagellin. CRKs possess extracellular Cys-rich domains and constitute a gene family consisting of 46 members in Arabidopsis. The single transfer DNA insertion lines CRK28 and CRK29, two CRKs induced in response to flagellin perception, did not exhibit robust alterations in immune responses. In contrast, silencing of multiple bacterial flagellin-induced CRKs resulted in enhanced susceptibility to pathogenic Pseudomonas syringae, indicating functional redundancy in this large gene family. Enhanced expression of CRK28 in Arabidopsis increased disease resistance to P. syringae. Expression of CRK28 in Nicotiana benthamiana induced cell death, which required intact extracellular Cys residues and a conserved kinase active site. CRK28-mediated cell death required the common receptor-like protein kinase coreceptor BAK1. CRK28 associated with BAK1 as well as the activated FLAGELLIN-SENSING2 (FLS2) immune receptor complex. CRK28 self-associated as well as associated with the closely related CRK29. These data support a model where Arabidopsis CRKs are synthesized upon pathogen perception, associate with the FLS2 complex, and coordinately act to enhance plant immune responses.

Parental DNA Methylation States Are Associated with Heterosis in Epigenetic Hybrids

“…In addition, another candidate gene (AT4G21860) was up-regulated in the same epiHybrid. Five of the six genes (AT4G21400, AT4G21410, AT4G21650, AT4G21830, and AT4G21860) were interesting in terms of their functionality, as they were shown to be involved in stress or defense responses (Rizhsky et al, 2004;Laugier et al, 2010;Li et al, 2012;Yadeta et al, 2017). The down-regulation of two (AT4G21650 and AT4G21830) of these genes was observed previously in heterotic hybrids between different Arabidopsis accessions .…”

Receptor Kinases in Plant-Pathogen Interactions: More Than Pattern Recognition

“…Similar to the FLS2-FER interaction, the Arabidopsis malectin-like/LRR-RLK IMPAIRED OOMYCETE SUSCEPTIBILITY1 (IOS1) was recently shown to interact with FLS2, EFR, and CERK1 and contributes to pattern-triggered immunity (Yeh et al, 2016). Furthermore, a cysteine-rich RLK, CPK28, was recently shown to interact with FLS2 and positively regulate disease resistance and cell death (Yadeta et al, 2017). A direct interaction between different receptor complexes may facilitate crosstalk between different pathways.…”

Bound by Fate: The Role of Reactive Oxygen Species in Receptor-Like Kinase Signaling

“…CRKs are involved in ROS-related processes, such as the regulation of MAMP-induced ROS production and stomatal closure (Bourdais et al, 2015). Furthermore, CRKs associate with other RLKs, such as FLS2 (Yeh et al, 2015) and BAK1 (Yadeta et al, 2016). Taken together, this emerging evidence supports a potential role for CRKs in the regulation of ROS production by RBOHs.…”

“…Transcriptional regulation by apoplastic ROS, the presence of conserved cysteines in the ectodomain, and functional analysis of crk mutants suggest that CRKs are intricately involved in ROS signaling (Chen, 2001;Bourdais et al, 2015). The recent report of a cysteine-dependent function for CRK28 (Yadeta et al, 2016) further supports this hypothesis. However, it will be critical to investigate whether the cysteines in the CRK ectodomains fulfill signaling functions or are purely relevant for the structure of the domain.…”