Plants produce linalool to respond to biotic stress, but the linalool-induced early signal remains unclear. In wild-type Arabidopsis, plant resistance to diamondback moth (Plutella xylostella) increased more strongly in a linalool-treated group than in an untreated control group. H2O2 and Ca2+, two important early signals that participated in biotic stress, burst after being treated with linalool in Arabidopsis mesophyll cells. Linalool treatment increased H2O2 and intracellular calcium concentrations in mesophyll cells, observed using a confocal microscope with laser scanning, and H2O2 signaling functions upstream of Ca2+ signaling by using inhibitors and mutants. Ca2+ efflux was detected using non-invasive micro-test technology (NMT), and Ca2+ efflux was also inhibited by NADPH oxidase inhibitor DPI (diphenyleneiodonium chloride) and in cells of the NADPH oxidase mutant rbohd. To restore intracellular calcium levels, Ca2+-ATPase was activated, and calmodulin 3 (CAM3) participated in Ca2+-ATPase activation. This result is consistent with the interaction between CAM7 and Ca2+-ATPase isoform 8 (ACA8). In addition, a yeast two-hybrid assay, firefly luciferase complementation imaging assay, and an in vitro pulldown assay showed that CAM3 interacts with the N-terminus of ACA8, and qRT-PCR showed that some JA-related genes and defense genes expressions were enhanced when treated with linalool in Arabidopsis leaves. This study reveals that linalool enhances H2O2 and intracellular calcium concentrations in Arabidopsis mesophyll cells; CAM3-ACA8 reduces intracellular calcium concentrations, allowing cells to resume their resting state. Additionally, JA-related genes and defense genes' expression may enhance plants' defense when treated with linalool.
Keywords: CAM3-ACA8; H2O2 signaling; Plutella xylostella; calcium signaling; linalool.