Expression of Allene Oxide Synthase Determines Defense Gene Activation in Tomato

Abstract

Allene oxide synthase (AOS; hydroperoxide dehydratase; EC 4.2.1.92) catalyzes the first step in the biosynthesis of jasmonic acid from lipoxygenase-derived hydroperoxides of free fatty acids. Using theAOS cDNA from tomato (Lycopersicon esculentum), in which the role of jasmonic acid in wound-induced defense gene activation has been best described, we examined the kinetics of AOS induction in response to wounding and elicitors, in parallel with that of the wound-inducible PIN II (proteinase inhibitor II) gene. AOS was induced in leaves by wounding, systemin, 12-oxophytodienoic acid, and methyl jasmonate. The levels of AOS mRNA started declining by 4 h after induction, whereas the levels of PIN II mRNA continued to increase up to 20 h after induction. Salicylic acid inhibited AOS and PIN IIexpression, and the addition of 12-oxophytodienoic acid or methyl jasmonate did not prevent the inhibition of PIN IIexpression in the presence of salicylic acid. Ethylene induced the expression of AOS, but the presence of ethylene alone did not produce an optimal induction of PIN II. The addition of silver thiosulfate, an ethylene action inhibitor, prevented the wound-induced expression of both AOS and PIN II. Products of hydroperoxide lyase affected neitherAOS nor PIN II, but induced expression of prosystemin. Based on these results, we propose an updated model for defense gene activation in tomato.

Jasmonic acid carboxyl methyltransferase: A key enzyme for jasmonate-regulated plant responses

“…It has been suggested that AOS is a major control point in the octadecanoid signaling pathway (42,43). However, overexpression of the plastidic flax AOS cDNA in transgenic potato plants was not enough to trigger a constitutive expression of wound-or jasmonate-responsive genes, even though the plants contained 6-to 12-fold increased levels of JA (11).…”

Lipid metabolism in arbuscular mycorrhizal roots of Medicago truncatula

“…The activity of several CYP74-enzymes has previously been described to be located in plastids [3]. Analysis of amino acid sequences of different cloned members of the CYP74 family revealed the presence of plastidic transit peptides [ 25,26,27]. The deduced amino acid sequence of AsDES lacks such a typical transit peptide.…”

Lipoxygenases and their metabolites in formation of plant stress tolerance

“…Gene expression of lipoxygenases and cytochrome oxides (СYР74) is regulated by JA and its derivatives [4,8,62]. Enhancement of aoS genes transcription in cells and increase in AOC activity occur when leaves are wounded [63]. Promoters of many genes of the enzyme family cytochrome oxidases were revealed to have elements sensitive to stress signals by JA, SA and ethylene [63,64].…”