Innate Immunity Signaling: Cytosolic Ca2+ Elevation Is Linked to Downstream Nitric Oxide Generation through the Action of Calmodulin or a Calmodulin-Like Protein  

Abstract

Ca2+ rise and nitric oxide (NO) generation are essential early steps in plant innate immunity and initiate the hypersensitive response (HR) to avirulent pathogens. Previous work from this laboratory has demonstrated that a loss-of-function mutation of an Arabidopsis (Arabidopsis thaliana) plasma membrane Ca 2+ -permeable inwardly conducting ion channel impairs HR and that this phenotype could be rescued by the application of a NO donor. At present, the mechanism linking cytosolic Ca 2+ rise to NO generation during pathogen response signaling in plants is still unclear. Animal nitric oxide synthase (NOS) activation is Ca 2+ / calmodulin (CaM) dependent. Here, we present biochemical and genetic evidence consistent with a similar regulatory mechanism in plants: a pathogen-induced Ca 2+ signal leads to CaM and/or a CaM-like protein (CML) activation of NOS. In wild-type Arabidopsis plants, the use of a CaM antagonist prevents NO generation and the HR. Application of a CaM antagonist does not prevent pathogen-induced cytosolic Ca 2+ elevation, excluding the possibility of CaM acting upstream from Ca 2+ . The CaM antagonist and Ca 2+ chelation abolish NO generation in wild-type Arabidopsis leaf protein extracts as well, suggesting that plant NOS activity is Ca 2+ /CaM dependent in vitro. The CaM-like protein CML24 has been previously associated with NO-related phenotypes in Arabidopsis. Here, we find that innate immune response phenotypes (HR and [avirulent] pathogen-induced NO elevation in leaves) are inhibited in loss-of-function cml24-4 mutant plants. Pathogenassociated molecular pattern-mediated NO generation in cells of cml24-4 mutants is impaired as well. Our work suggests that the initial pathogen recognition signal of Ca 2+ influx into the cytosol activates CaM and/or a CML, which then acts to induce downstream NO synthesis as intermediary steps in a pathogen perception signaling cascade, leading to innate immune responses, including the HR.

Modulation of Protein Phosphorylation, N-Glycosylation and Lys-Acetylation in Grape (Vitis vinifera) Mesocarp and Exocarp Owing to Lobesia botrana Infection

“…3B) is a tryptic fragment of the "EF-hand calcium-binding protein," which is orthologous to the "calcium-binding protein CML (CaMCML)." This protein seems to have a pivotal role in the plant innate immune system by inducing NO generation through the nitric oxide synthase (NOS) activation upon plant infection (43). Fig.…”

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

“…It is unclear whether Ca 2+ /CaM can directly modulate plant NOS or if Ca 2+ /CaM impacts plant leaf development/ senescence through (either direct or indirect) effects on NO generation. However, recent studies from our lab suggest that Ca 2+ /CaM acts as an activator of NOS activity in plant innate immune response signaling Ma et al, 2008).…”

“…generation of NO from L-Arg) is greatly reduced in senescing leaves. Plant NOS activity is regulated by Ca 2+ /calmodulin (CaM; Delledonne et al, 1998;Corpas et al, 2004Corpas et al, , 2009del Río et al, 2004;Valderrama et al, 2007;Ma et al, 2008). These studies suggest a link between Ca 2+ and NO that could be operating during senescence.…”

Plant Stress Surveillance Monitored by ABA and Disease Signaling Interactions

“…One of the major responses by infectioninduced cytosolic Ca 2+ influx is the generation of hypersensitive response (HR) and ROS production. Moreover pharmacological experiments with Calmodulin (CaM) antagonist and the calmodulin-like24-4 (cml24-4) mutant demonstrated that Ca 2+ influx mediates generation of Nitric oxide (NO) signals through activation of CaM or CML (Ma et al, 2008). For the decoding of pathogen-induced Ca 2+ signature, AtSR1 also known as Ca 2+ /calmodulin-binding transcription factor3 (CAMTA3) acts as a negative regulator of SA signaling-mediated HRs by binding to the promoter of the EDS1 gene (Du et al, 2009).…”