The Arabidopsis her1 mutant implicates GABA in E‐2‐hexenal responsiveness

Abstract

SummaryWhen wounded or attacked by herbivores or pathogens, plants produce a blend of six-carbon alcohols, aldehydes and esters, known as C6-volatiles. Undamaged plants, when exposed to C6-volatiles, respond by inducing defense-related genes and secondary metabolites, suggesting that C6-volatiles can act as signaling molecules regulating plant defense responses. However, to date, the molecular mechanisms by which plants perceive and respond to these volatiles are unknown. To elucidate such mechanisms, we decided to isolate Arabidopsis thaliana mutants in which responses to C6-volatiles were altered. We observed that treatment of Arabidopsis seedlings with the C6-volatile E-2-hexenal inhibits root elongation. Among C6-volatiles this response is specific to E-2-hexenal, and is not dependent on ethylene, jasmonic and salicylic acid. Using this bioassay, we isolated 18 E-2-hexenal-response (her) mutants that showed sustained root growth after E-2-hexenal treatment. Here, we focused on the molecular characterization of one of these mutants, her1. Microarray and map-based cloning revealed that her1 encodes a c-amino butyric acid transaminase (GABA-TP), an enzyme that degrades GABA. As a consequence of the mutation, her1 plants accumulate high GABA levels in all their organs. Based on the observation that E-2-hexenal treatment induces GABA accumulation, and that high GABA levels confer resistance to E-2-hexenal, we propose a role for GABA in mediating E-2-hexenal responses.

Plant Defense Priming against Herbivores: Getting Ready for a Different Battle

“…For example, changes may occur in cellular electrical potential or Ca 21 flux across cell membranes, as has been shown for physical damage (Maffei et al, 2007). Although such ephemeral signals by themselves are unlikely to maintain a primed state, the recent work in Arabidopsis linking g-amino butyric acid with responsiveness to E-2-hexenal provides an intriguing signaling cascade mechanism because wound-induced accumulation of g-amino butyric acid is regulated by the activity of a Ca 21 /calmodulin-dependent Glu decarboxylase (Mirabella et al, 2008).…”

Airborne Induction and Priming of Plant Defenses against a Bacterial Pathogen

“…Which VOCs, then, were responsible for the responses that we observed? Green-leaf volatiles have repeatedly been reported to be active in airborne induction of herbivore resistance (Engelberth et al, 2004;Farag et al, 2005;Ruther and Kleier, 2005;Mirabella et al, 2008), and they can also enhance a plant's direct resistance to certain pathogens, particularly necrotrophic fungi (Kishimoto et al, 2005;Matsui, 2006;Shiojiri et al, 2006). Certain volatiles even might be involved in the resistance of plants to abiotic stress (Behnke et al, 2007), and BTH treatment has been reported to enhance the attractiveness of herbivore-damaged corn seedlings to parasitic wasps (Rostás and Turlings, 2008).…”

Plant volatiles regulate the activities of Ca2+-permeable channels and promote cytoplasmic calcium transients in Arabidopsis leaf cells

“…(Described concentrations of volatiles seedlings. 23 In plant lines that are mutant for γ-amino butylic acid (GABA) transaminase, (E)-2-hexenal-dependent growth inhibition was impaired and GABA accumulation was observed. 22 Besides these biological and physiological effects, natural plant aldehydes including (E)-2-hexenal were identified as natural insecticides against stored-product beetles in fumigation tests with wheat grains.…”