The Ca²⁺ Channel CNGC19 Regulates Arabidopsis Defense Against Spodoptera Herbivory

Abstract

Cellular calcium elevation is an important signal used by plants for recognition and signaling of environmental stress. Perception of the generalist insect, <i>Spodoptera litura</i>, by Arabidopsis (<i>Arabidopsis thaliana</i>) activates cytosolic Ca²⁺ elevation, which triggers downstream defense. However, not all the Ca²⁺ channels generating the signal have been identified, nor are their modes of action known. We report on a rapidly activated, leaf vasculature- and plasma membrane-localized, CYCLIC NUCLEOTIDE GATED CHANNEL19 (CNGC19), which activates herbivory-induced Ca²⁺ flux and plant defense. Loss of <i>CNGC19</i> function results in decreased herbivory defense. The <i>cngc19</i> mutant shows aberrant and attenuated intravascular Ca²⁺ fluxes. CNGC19 is a Ca²⁺-permeable channel, as hyperpolarization of CNGC19-expressing <i>Xenopus</i> oocytes in the presence of both cyclic adenosine monophosphate and Ca²⁺ results in Ca²⁺ influx. Breakdown of Ca²⁺-based defense in <i>cngc19</i> mutants leads to a decrease in herbivory-induced jasmonoyl-l-isoleucine biosynthesis and expression of JA responsive genes. The <i>cngc19</i> mutants are deficient in aliphatic glucosinolate accumulation and hyperaccumulate its precursor, methionine. CNGC19 modulates aliphatic glucosinolate biosynthesis in tandem with BRANCHED-CHAIN AMINO ACID TRANSAMINASE4, which is involved in the chain elongation pathway of Met-derived glucosinolates. Furthermore, CNGC19 interacts with herbivory-induced CALMODULIN2 in planta. Together, our work reveals a key mechanistic role for the Ca²⁺ channel CNGC19 in the recognition of herbivory and the activation of defense signaling.