Inoculation of leaves of Arabidopsis thaliana (L.) Heynh. with the wheat pathogen, Pseudomonas syringae pv syringae, resulted in the expression of the hypersensitive reaction and in phytoalexin accumulation. No phytoalexin accumulation was detected after infiltration of leaves with a mutant of P. s. syringae deficient in the ability to elicit a hypersensitive reaction; with the crucifer pathogen, Xanthomonas campestris pv campestris; or with 10 milimolar potassium phosphate buffer (pH 6.9). Phytoalexin accumulation was correlated with the restricted in vivo growth of P. s. syringae. A phytoalexin was purified by a combination of reverse phase flash chromatography, thin layer chromatography, followed by reverse phase high performance liquid chromatography. The Arabidopsis phytoalexin was identified as 3-thiazol-2'-yl-indole on the basis of ultraviolet, infrared, mass spectral, 1H-nuclear magnetic resonance, and '3C-nuclear magnetic resonance data.Phytoalexins are low mol wt, antimicrobial compounds of plant origin that accumulate after inoculation with a plant pathogen (14). A number of observations support the hypothesis that phytoalexins play a role in the defense response of plants to pathogens. Phytoalexins are absent in healthy tissues and accumulate after infection by fungal (18,24,30) or bacterial (9, 1 1) pathogens in monocotyledonous plants (24) as well as in dicotyledonous plants (9,18,30). Phytoalexins have been demonstrated to accumulate rapidly at the site of attempted infection in sufficient quantities to inhibit the in vitro growth of fungi (18,30) and bacteria (9). Virulence of the fungus Nectria haematococca on pea is correlated with the ability to detoxify the phytoalexin pisatin (28). Furthermore, transformation of Cochliobolus heterostrophus with the gene encoding pisatin demethylase allowed this maize patho-
, lllinois 61 604 (T.H.)The gene encoding trichodiene synthase (Trit;), a sesquiterpene synthase from the fungus Fusarium sporofrichioides, was used t o transform tobacco (Nicotiana tabacum). Trichodiene was the sole sesquiterpene synthase product in enzyme reaction mixtures derived from unelicited transformant cell-suspension cultures, and both trichodiene and 5-epi-aristolochene were observed as reaction products following elicitor treatment. lmmunoblot analysis of protein extracts revealed the presence of trichodiene synthase only in transformant cell lines producing trichodiene. In vivo labeling with [3Hlmevalonate revealed the presence of a novel trichodiene metabolite, 1 5-hydroxytrichodiene, that accumulated in the transformant cell-suspension cultures. I n a trichodiene-producing transformant, the leve1 of 1 5-hydroxytrichodiene accumulation increased after elicitor treatment. In vivo labeling with [14C1acetate showed that the biosynthetic rate of trichodiene and 15-hydroxytrichodiene also increased after elicitor treatment. lncorporation of radioactivity from [14C]acetate into capsidiol was reduced following elicitor treatment of a trichodiene-producing transformant as compared with wild type. These results demonstrate that sesquiterpenoid accumulation resulting from the constitutive expression of a foreign sesquiterpene synthase is responsive t o elicitation and that the farnesyl pyrophosphate present in elicited cells can be utilized by a foreign sesquiterpene synthase t o produce high levels of novel sesquiterpenoids.Sesquiterpenoids are thought to be prominent in plantfungal interactions. Members of this structurally diverse group of cyclic terpenoids appear to function both as defensive compounds in plants and as virulence factors in fungal plant pathogens. The best characterized examples of this include the accumulation of antimicrobial sesquiterpenoids in tobacco (Nicotiana tabacum) and other Solanaceae following exposure to fungi or fungal cell-wall fragments (Vogeli and Chappell, 1988; Zook and Kuc, 1991) and the production of phytotoxic sesquiterpenoids by fungal plant pathogens that enhance their virulence on certain plant hosts (Proctor et al., 1995). Sesquiterpenoids also frequently occur as components of plant essential oils and contribute to the flavor and fragrance of some agricultura1 products (Templeton, 1969).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.