The Arabidopsis Cyclic Nucleotide-Gated Ion Channels AtCNGC2 and AtCNGC4 Work in the Same Signaling Pathway to Regulate Pathogen Defense and Floral Transition      

Abstract

Arabidopsis (Arabidopsis thaliana) cyclic nucleotide-gated ion channels (CNGCs) form a large family consisting of 20 members and have been implicated in Ca 2+ signaling related to various physiological processes, such as pathogen defense, development, and thermotolerance. The null mutant of AtCNGC2, defense, no death (dnd1), exhibits autoimmune phenotypes, while it is impaired in mounting the hypersensitive response, which is a hallmark of effector-triggered (i.e. RESISTANCE-gene mediated) resistance. It has been suggested that AtCNGC2 is involved in defense responses and likely other aspects of physiology through its role as a Ca 2+ -conducting channel. However, the downstream signaling components and its relation with AtCNGC4, which is the closest paralog of AtCNGC2, remain elusive. Despite the fact that cngc4 mutants display almost identical phenotypes to those seen in cngc2 mutants, not much is known about their relationship. Here, we report the identification and characterization of the Arabidopsis mutant repressor of defense no death1 (rdd1), obtained from a suppressor screen of a transfer DNA insertion knockout mutant of AtCNGC2 in order to identify downstream components of dnd1-mediated signal transduction. rdd1 suppressed the majority of dnd1-mediated phenotypes except Ca 2+ hypersensitivity. In addition, rdd1 also suppressed the dnd1-mediated lateflowering phenotype that was discovered in this study. Our genetic analysis conducted to elucidate the relationship between AtCNGC2 and AtCNGC4 indicates that RDD1 is also involved in AtCNGC4-mediated signal transduction. Lastly, bimolecular fluorescence complementation analysis suggests that AtCNGC2 and AtCNGC4 are likely part of the same channel complex.

Genetic buffering of cyclic AMP in Arabidopsis thaliana compromises the plant immune response triggered by an avirulent strain of Pseudomonas syringae pv. tomato

“…It is therefore tempting to assume a possible regulation of the SA‐dependent pathway by cAMP through cytosolic Ca 2+ homeostasis modulation. Much evidence indicates that cAMP permits Ca 2+ entrance into plant cells through CNGCs, initiating that the signalling event cascades occurred in response to biotic stress (Clough et al ., ; Balagué et al ., ; Jurkowski et al ., ; Yoshioka et al ., ; Ali et al ., ; Chin et al ., ; Lu et al ., ). Our data suggested that the delay in HR activation could be in part due to a failure in the activation of CNGCs in cAS plants, although we cannot exclude a possible downregulation of Ca 2+ efflux transporters in our system (Bose et al ., ).…”

OsCNGC13 promotes seed-setting rate by facilitating pollen tube growth in stylar tissues

“…The leaves of null mutant of AtCNGC2 , defense , no death ( dnd1 ), display delayed PCD when challenged with pathogens [22]. Null mutants of AtCNGC4 (the closest paralog of AtCNGC2 ) exhibit remarkably similar phenotypes to dnd1 [62, 63], supporting a notion that AtCNGC2 and AtCNGC4 may form a heteromeric Ca 2+ channel complex [54]. Similarly, several recent studies also documented evidence for a role of AtCNGC11 and AtCNGC12 in PCD and plant immunity [21, 23, 24, 26].…”

“…AtCNGC2 was co-expressed with AtCNGC4 as the positive control [54]. For transient expression, the Agrobacterium tumefaciens strain EHA105 carrying the BiFC constructs were co-infiltrated into N .…”

Ca2+ signalling in plant immune response: from pattern recognition receptors to Ca2+ decoding mechanisms

“…A second class of potential Ca 2+ channels are the cyclic nucleotide gated channels (CNGCs). Their initial implication in plant defence response comes from mutant studies where the 'constitutive expresser of pathogenesis-related (PR) genes22 ' (cpr22) gene is the result of a genomic deletion creating an in-frame chimeric CNGC11-CNGC12 fusion (Yoshioka et al, 2006), or from the fact that the defence-no-death mutants, dnd1 and dnd2, are CNGC2 and CNGC4, respectively (Chin et al, 2013). Arabidopsis CNGC2/DND1 is implicated in the transduction of DAMP, Pep1, (Qi et al, 2010) and bacterial lipopolysaccharide (LPS)mediated reactions (Ali et al, 2007).…”