Methyl jasmonate signaling and signal crosstalk between methyl jasmonate and abscisic acid in guard cells

Abstract

Plants tightly control stomatal aperture in response to various environmental changes. A drought-inducible phytohormone, abscisic acid (ABA), triggers stomatal closure and ABA signaling pathway in guard cells has been well studied. Similar to ABA, methyl jasmonate (MeJA) induces stomatal closure in various plant species but MeJA signaling pathway is still far from clear. Recently we found that Arabidopsis calcium dependent protein kinase CPK6 functions as a positive regulator in guard cell MeJA signaling and provided new insights into cytosolic Ca2+-dependent MeJA signaling. Here we discuss the MeJA signaling and also signal crosstalk between MeJA and ABA pathways in guard cells.

Figure 1

Proposed MeJA signaling pathway and signal crosstalk between MeJA and ABA in Arabidopsis guard cells. MeJA induces ROS and NO production in guard cells. RCN1-regulating PP2As are involved in this step. The major ROS sourses are NAD(P)H oxidases AtrbohD/F. NOS activity seems to be important for MeJA-induced NO production, but genes encoding NOS have not been indentified in plants. ROS and NO evoke guard cell [Ca²⁺]_cyt elevation by Ca²⁺ influx from apoplast and from intracellular stores, respectively. I_Ca channels mediate Ca²⁺ influx from apoplast. Elevated [Ca²⁺]_cyt is sensed by CDPKs including CPK6 and finally activates S-type anion channels. The abi2-1 mutation disrupts ROS-mediated I_Ca channel activation. The abi2-1 mutation also disrupts NO-dependent signal pathway, but the details are still unclear. Two myrosinases TGG1 and TGG2 are also involved in the signal crosstalk.