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Stress-induced expression of a parsley gene encoding 4-coumarate:CoA-ligase

University of British Columbia

Many of the diverse end-products of the phenyipropanoid pathway play an important role in the response of plants to environmental stresses such as wounding and pathogen attack. A key enzyme in the general phenylpropanoid pathway is 4-coumarate:CoA ligase (4CL) which catalyses the formation of activated esters of hydroxycinnamic acids. Expression of the parsley genes encoding this enzyme is increased in response to wounding or challenge with a fungal elicitor from Phytophthora megasperma. Using a number different systems I have investigated the stress response of parsley 4 CL. Using transgenic tobacco as a heterologous system to study the wound response, I showed that the same fragment of the 4 CL-1 promoter mediates wound-responsiveness and a strong response to exogenously applied methyl jasmonate. The 4 CL-1 promoter also mediates responsiveness to linolenic acid, from which jasmonates are synthesised via a lipoxygenase mediated step. In parsley cells in suspension culture, linolenic acid also activates 4CL expression, and expression of a number of phenyipropanoid and other defense-related genes is induced by jasmonates in this system. A similar response to jasmonates is observed in whole parsley plants. Jasmonate treatment of parsley cells activates the expression of genes of the furanocoumarin specific branch pathway of phenylpropanoid metabolism and results in secretion of furanocoumarins (which are known phytoalexins in parsley) by the cell cultures. In the presence of an inhibitor of lipoxygenase activity, n-propylgallate, the response of 4CL to stress was decreased in both systems suggesting that de novo synthesis of jasmonates may be required for these stress responses. This suggests that jasmonates may mediate the stress responses of 4CL and other defense-related genes In transgenic Arabidopsis, the parsley 4 CL-1 promoter is responsive to endogenously generated wound signals and directed strong localised expression of the reporter gene GUS at wound-sites. This may provide the basis for a genetic screen to identify genes whose products are necessary for the wound response of 4 CL-1.

Thesis/Dissertation

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2009-04-08

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http://hdl.handle.net/2429/6901

Botany

University of British Columbia

UBCV

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