Functional Convergence of Oxylipin and Abscisic Acid Pathways Controls Stomatal Closure in Response to Drought    

Abstract

Membranes are primary sites of perception of environmental stimuli. Polyunsaturated fatty acids are major structural constituents of membranes that also function as modulators of a multitude of signal transduction pathways evoked by environmental stimuli. Different stresses induce production of a distinct blend of oxygenated polyunsaturated fatty acids, "oxylipins." We employed three Arabidopsis (Arabidopsis thaliana) ecotypes to examine the oxylipin signature in response to specific stresses and determined that wounding and drought differentially alter oxylipin profiles, particularly the allene oxide synthase branch of the oxylipin pathway, responsible for production of jasmonic acid (JA) and its precursor 12-oxo-phytodienoic acid (12-OPDA). Specifically, wounding induced both 12-OPDA and JA levels, whereas drought induced only the precursor 12-OPDA. Levels of the classical stress phytohormone abscisic acid (ABA) were also mainly enhanced by drought and little by wounding. To explore the role of 12-OPDA in plant drought responses, we generated a range of transgenic lines and exploited the existing mutant plants that differ in their levels of stress-inducible 12-OPDA but display similar ABA levels. The plants producing higher 12-OPDA levels exhibited enhanced drought tolerance and reduced stomatal aperture. Furthermore, exogenously applied ABA and 12-OPDA, individually or combined, promote stomatal closure of ABA and allene oxide synthase biosynthetic mutants, albeit most effectively when combined. Using tomato (Solanum lycopersicum) and Brassica napus verified the potency of this combination in inducing stomatal closure in plants other than Arabidopsis. These data have identified drought as a stress signal that uncouples the conversion of 12-OPDA to JA and have revealed 12-OPDA as a drought-responsive regulator of stomatal closure functioning most effectively together with ABA.

Alterations of Endogenous Hormonal Levels in Plants under Drought and Salinity

“…This finding suggests that OPDA might participate in the mechanisms that confer tolerance to water stress in B71 seedlings (Andrade, unpublished data). In concordance, [41] demonstrated that Arabidopsis plants producing higher OPDA levels exhibited a reduction in the stomatal aperture, and as result enhanced drought tolerance (Figure 2). It should be pointed out that this study confirmed OPDA as a drought-responsive regulator of stomatal closure which might act effectively together with ABA in this response.…”

Stomatal Defense a Decade Later

“…In particular, methylated JA (MeJA) has been used extensively to elucidate JA-dependent responses. Although some studies have provided evidence that MeJA closes the stomatal pore (Suhita et al, 2004;Munemasa et al, 2007;DesclosTheveniau et al, 2012;Hua et al, 2012;Yan et al, 2015), this could not be verified by other research groups (Speth et al, 2009;Savchenko et al, 2014). This inconsistency might be explained by the fact that an endogenous ABA threshold is needed for MeJA-induced stomatal closure (Hossain et al, 2011).…”

Spatial expression of the Arabidopsishydroperoxide lyasegene is controlled differently from that of theallene oxide synthasegene

“…Froehlich et al (2001) showed that tomato HPL and AOS are targeted to the outer and inner membranes of the chloroplast envelope, respectively. Rice HPL3 (OsHPL3), which has the shortest extension of its N-terminal among the three HPLs, was transported to chloroplasts when a fusion protein of the transit peptide of OsHPL3 with green fluorescent protein (GFP) was expressed in Arabidopsis leaves (Savchenko et al 2014). However, localization of HPL in Arabidopsis has not been reported.…”