Death Don't Have No Mercy and Neither Does Calcium: Arabidopsis CYCLIC NUCLEOTIDE GATED CHANNEL2 and Innate Immunity

Abstract

Plant innate immune response to pathogen infection includes an elegant signaling pathway leading to reactive oxygen species generation and resulting hypersensitive response (HR); localized programmed cell death in tissue surrounding the initial infection site limits pathogen spread. A veritable symphony of cytosolic signaling molecules (including Ca2+, nitric oxide [NO], cyclic nucleotides, and calmodulin) have been suggested as early components of HR signaling. However, specific interactions among these cytosolic secondary messengers and their roles in the signal cascade are still unclear. Here, we report some aspects of how plants translate perception of a pathogen into a signal cascade leading to an innate immune response. We show that Arabidopsis thaliana CYCLIC NUCLEOTIDE GATED CHANNEL2 (CNGC2/DND1) conducts Ca2+ into cells and provide a model linking this Ca2+ current to downstream NO production. NO is a critical signaling molecule invoking plant innate immune response to pathogens. Plants without functional CNGC2 lack this cell membrane Ca2+ current and do not display HR; providing the mutant with NO complements this phenotype. The bacterial pathogen–associated molecular pattern elicitor lipopolysaccharide activates a CNGC Ca2+ current, which may be linked to NO generation due to buildup of cytosolic Ca2+/calmodulin.

Lesion mimic mutants

“…10 However, only Ca 2+ channel inhibitors such as Gd 3+ or La 3+ significantly suppressed HR formation induced by cpr22 (AtCNGC11/12), but not the K + channel blocker, tetraethylammonium chloride (TEA). 23 The same effects were reported by Ali et al, 53 for AtCNGC2. This indicates that Ca 2+ influx, at least in part mediated by CNGCs plays a crucial role in the induction of PCD.…”

“…For examples, AtCNGC2 has been shown by patch clamp and yeast complementation analysis to be an inward rectifying Ca 2+ and K + channel. 52,53 AtCNGC11 and 12 also conduct Ca 2+ and K + as shown by yeast complementation assays. 7,23 AtCNGC4 is permeable for both Na + and K + .…”

Unraveling the Tapestry of Networks Involving Reactive Oxygen Species in Plants

“…These include Bax inhibitor 1 (Watanabe and Lam, 2008), BAP1 and BAP2 , the receptor kinase CERK1 (Miya et al, 2007), and BAK1 Kemmerling et al, 2007). Cyclic nucleotide-gated channel 2 (also called DND1) also was described as a key mediator of NO and hypersensitive response cell death (Ali et al, 2007). These studies provide important links between signaling events that occur upstream or downstream of ROS production during pathogen attack and expose the chronology of events that imparts successful defense against pathogens.…”

Leaf Senescence Signaling: The Ca2+-Conducting Arabidopsis Cyclic Nucleotide Gated Channel2 Acts through Nitric Oxide to Repress Senescence Programming

“…Plant cyclic nucleotide gated channels (CNGCs) have been proposed as candidates to conduct extracellular Ca 2+ into the cytosol (Sunkar et al, 2000;Talke et al, 2003;Lemtiri-Chlieh and Berkowitz, 2004;Ali et al, 2007;Demidchik and Maathuis, 2007;Frietsch et al, 2007;Kaplan et al, 2007;Ma and Berkowitz, 2007;Urquhart et al, 2007;Ma et al, 2009aMa et al, , 2009b. Arabidopsis "defense, no death" (dnd1) mutant plants have a null mutation in the gene encoding the plasma membranelocalized Ca 2+ -conducting CNGC2 channel.…”