Phytoalexin

About: Phytoalexin is a research topic. Over the lifetime, 1161 publications have been published within this topic receiving 63405 citations. The topic is also known as: phytoalexins.

A Stress-Inducible Resveratrol O-Methyltransferase Involved in the Biosynthesis of Pterostilbene

Abstract: Stilbenes are considered the most important phytoalexin group in grapevine (Vitis vinifera) and they are known to contribute to the protection against various pathogens. The main stilbenes in grapevine are resveratrol and its derivatives and, among these, pterostilbene has recently attracted much attention due both to its antifungal and pharmacological properties. Indeed, pterostilbene is 5 to 10 times more fungitoxic than resveratrol in vitro and recent studies have shown that pterostilbene exhibits anticancer, hypolipidemic, and antidiabetic properties. A candidate gene approach was used to identify a grapevine resveratrol O-methyltransferase (ROMT) cDNA and the activity of the corresponding protein was characterized after expression in Escherichia coli. Transient coexpression of ROMT and grapevine stilbene synthase in tobacco (Nicotiana benthamiana) using the agroinfiltration technique resulted in the accumulation of pterostilbene in tobacco tissues. Taken together, these results showed that ROMT was able to catalyze the biosynthesis of pterostilbene from resveratrol both in vitro and in planta. ROMT gene expression in grapevine leaves was induced by different stresses, including downy mildew (Plasmopara viticola) infection, ultraviolet light, and AlCl3 treatment.

Modulation of Phytoalexin Biosynthesis in Engineered Plants for Disease Resistance

Abstract: Phytoalexins are antimicrobial substances of low molecular weight produced by plants in response to infection or stress, which form part of their active defense mechanisms. Starting in the 1950's, research on phytoalexins has begun with biochemistry and bio-organic chemistry, resulting in the determination of their structure, their biological activity as well as mechanisms of their synthesis and their catabolism by microorganisms. Elucidation of the biosynthesis of numerous phytoalexins has permitted the use of molecular biology tools for the exploration of the genes encoding enzymes of their synthesis pathways and their regulators. Genetic manipulation of phytoalexins has been investigated to increase the disease resistance of plants. The first example of a disease resistance resulting from foreign phytoalexin expression in a novel plant has concerned a phytoalexin from grapevine which was transferred to tobacco. Transformations were then operated to investigate the potential of other phytoalexin biosynthetic genes to confer resistance to pathogens. Unexpectedly, engineering phytoalexins for disease resistance in plants seem to have been limited to exploiting only a few phytoalexin biosynthetic genes, especially those encoding stilbenes and some isoflavonoids. Research has rather focused on indirect approaches which allow modulation of the accumulation of phytoalexin employing transcriptional regulators or components of upstream regulatory pathways. Genetic approaches using gain- or less-of functions in phytoalexin engineering together with modulation of phytoalexin accumulation through molecular engineering of plant hormones and defense-related marker and elicitor genes have been reviewed.

Induction of Defense Responses in Cultured Parsley Cells by Plant Cell Wall Fragments

Abstract: Cell suspension cultures of parsley (Petroselinum crispum) accumulated coumarin phytoalexins and exhibited increased β-1,3-glucanase activity when treated with either a purified α-1,4-d-endopolygalacturonic acid lyase from Erwinia carotovora or oligogalacturonides solubilized from parsley cell walls by endopolygalacturonic acid lyase. Coumarin accumulation induced by the plant cell wall elicitor was preceded by increases in the activities of phenylalanine ammonia lyase (PAL), 4-coumarate:CoA ligase (4CL) and S-adenosyl-l-methionine:xanthotoxol O-methyltransferase (XMT). The time courses for the changes in these three enzyme activities were similar to those observed in cell cultures treated with a fungal glucan elicitor. The plant cell wall elicitor was found to act synergistically with the fungal glucan elicitor in the induction of coumarin phytoalexins. As much as a 10-fold stimulation in coumarin accumulation above the calculated additive response was observed in cell cultures treated with combinations of plant and fungal elicitors. The synergistic effect was also observed for the induction of PAL, 4CL, and XMT activities. These results demonstrate that plant cell wall elicitors induce at least two distinct biochemical responses in parsley cells and further support the role of oligogalacturonides as important regulators of plant defense.

Microbial elicitors of plant defence responses activate transcription of a retrotransposon

Abstract: Summary The Tnt1 retrotransposon was isolated from tobacco after transposition. Tnt1 expression is very low at the plant level and under most stress conditions but is strongly induced during protoplast isolation. It is shown here that transcription of the Tnt1 retrotransposon can be activated by several microbial factors having the common ability to elicit a hypersensitive response in tobacco. These elicitors include Onozuka crude extracts from the fungus Trichoderma viride, elicitins purified from Phytophthora fungal species and culture supernatants of the bacterium Erwinia chrysanthemi. Activation of Tnt1 expression correlates with the biological activity of purified elicitins. On detached leaves, dose response to two different elicitins, the highly necrotic cryptogein from P. cryptogea and the less toxic capsicein from P. capsici, is parallel to the necrotic dose response. A dose of 1 µg cryptogein induces Tnt1 transcription to a high level similar to that induced by Onozuka 1 mg ml−1 whilst 10–100-fold more capsicein is required to induce this level. In whole plants treated with cryptogein, activation of Tnt1 transcription is restricted to necrotic organs. In tobacco cell suspension cultures treated with E. chrysanthemi culture supernatants, the accumulation of Tnt1 RNA correlates with the accumulation of the phytoalexin capsidiol a few hours later. Two hours after contact with the elicitor, cells accumulate a high level of Tnt1 RNA, this level being almost 10-fold higher than that observed in protoplasts in response to Onozuka 1 mg ml−1. Our results suggest that Tnt1 activation might reflect a local and early plant response to microbial stress.