Abstract
Key messageThis work adds a new player, HER2, downstream of the perception of E-2-hexenal, a green leaf volatile, and shows that E-2-hexenal specifically changes the redox status of the mitochondria.It is widely accepted that plants produce and respond to green leaf volatiles (GLVs), but the molecular components involved in transducing their perception are largely unknown. The GLV E-2-hexenal inhibits root elongation in seedlings and, using this phenotype, we isolated E-2-hexenal response (her) Arabidopsis thaliana mutants. Using map-based cloning we positioned the her2 mutation to the At5g63620 locus, resulting in a phenylalanine instead of serine on position 223. Knockdown and overexpression lines of HER2 confirmed the role of HER2, which encodes an oxidoreductase, in the responsiveness to E-2-hexenal. Since E-2-hexenal is a reactive electrophile species, which are known to influence the redox status of cells, we utilized redox sensitive GFP2 (roGFP2) to determine the redox status of E-2-hexenal-treated root cells. Since the signal peptide of HER2 directed mCherry to the mitochondria, we targeted the expression of roGFP2 to this organelle besides the cytosol. E-2-hexenal specifically induced a change in the redox status in the mitochondria. We did not see a difference in the redox status in her2 compared to wild-type Arabidopsis. Still, the mitochondrial redox status did not change with Z-3-hexenol, another abundant GLV. These results indicate that HER2 is involved in transducing the perception of E-2-hexenal, which changes the redox status of the mitochondria.
Highlights
Green leaf volatiles are C 6 volatiles, which are produced by plants in response to herbivory, wounding and environmental stress (Croft et al 1993; Fall et al 1999; Gouinguené and Turlings 2002; Heiden et al 2003; Shiojiri et al 2000, 2006; Turlings et al 1995)
In a previous paper (Mirabella et al 2008) we described the isolation of different hexenal response mutants and we showed that the her1 mutation was in the glutamate to γ-amino butyric acid (GABA) transaminase gene (At3g22200)
The her2 mutant has a similar phenotype as the her1 mutant (Mirabella et al 2008), i.e. the growth of the root of young seedlings is less inhibited by 0.3 μM aerial E-2-hexenal than the wild type Arabidopsis ecotype Col-0 of which the root stops growing (Fig. 1a)
Summary
Green leaf volatiles are C 6 volatiles, which are produced by plants in response to herbivory, wounding and environmental stress (Croft et al 1993; Fall et al 1999; Gouinguené and Turlings 2002; Heiden et al 2003; Shiojiri et al 2000, 2006; Turlings et al 1995) Biosynthesis of these volatiles occurs mainly from α-linolenic acid by the sequential action of two enzymes, a lipoxygenase (LOX), which dioxygenates at the C13 position, and hydroperoxide lyase (HPL; Hatanaka 1993; Matsui 2006; Matsui et al 2000; Mochizuki et al 2016), followed by the activity of an aldehyde dehydrogenase (ADH), an isomerase (Kunishima et al 2016) and acetyltransferase (D’Auria et al 2007) in order to produce the GLV bouquet of C6-aldehydes, alcohols and their esters. Plants have developed a repertoire of enzymatic reactions to modify GLVs upon perception (Matsui 2016), reducing them (Matsui et al 2012), converting them to glycosides (Sugimoto et al 2014, 2015) or glutathione conjugates (Davoine et al 2006; Mirabella et al 2008)
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