Spatio-temporal expression of patatin-like lipid acyl hydrolases and accumulation of jasmonates in elicitor-treated tobacco leaves are not affected by endogenous levels of salicylic acid

We have previously isolated three tobacco genes (NtPat) encoding patatin-like proteins, getting rapidly induced during the hypersensitive response (HR) to tobacco mosaic virus, in advance to jasmonate accumulation. NtPAT enzymes are lipid acyl hydrolases that display high phospholipase A(2) (PLA(2)) activity and may mobilize fatty acid precursors of oxylipins. Here, we performed a detailed study of NtPat gene regulation under various biotic and abiotic stresses. PLA(2) activity was poorly induced in response to drought, wounding, reactive oxygen intermediates, salicylic acid (SA) or methyl-jasmonate ( MJ) whereas the ethylene (ET) precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), provoked a moderate induction. In contrast, PLA(2) activity was strongly induced when ACC was combined with MJ, and in response to the bacterium Erwinia carotovora or to the fungus Botrytis cinerea, as well as to treatment with beta-megaspermin, a cell death-inducing protein elicitor. A simplified system based on the infiltration of beta-megaspermin into leaves was used to dissect the spatio-temporal activation of PLA(2) activity with regards to the accumulation of jasmonates and to the influence of endogenous SA. NtPat-encoded PLA(2) activity was rapidly induced in the infiltrated zone before the appearance of cell death and with some delay in the surrounding living cells. A massive accumulation of 12-oxo-phytodienoic and jasmonic acids occurred in the elicitor-infiltrated zone, but only low levels were detectable outside this area. A similar picture was found in SA-deficient plants, showing that in tobacco, accumulation of jasmonates is not affected by the concomitant HR-induced build-up of endogenous SA. Finally, ET-insensitive plants showed a weakened induction of PLA(2) activity outside the elicitor-infiltrated tissue.