Developmental and wound-induced regulation of 3-deoxy-D-arabino-heptulosonate 7-phosphate (DAHP) synthase in the Solanaceae

John Mark Henstrand, Purdue University

Abstract

Wounding of plant tissues induces a massive change in gene expression. The phytohormone ethylene which is evolved in response to wounding of plant tissues has been implicated as one of the mediators of wound-induced changes in gene expression. Wounded unripe tomato pericarp tissue was treated with either 2,5 norbornadiene or silver thiosulfate to specifically inhibit the expression of ethylene-regulated mRNA species. Results show that wounding induces a dramatic shift in gene expression (over 50 mRNA species), but expression of less than 15% of these genes is affected by the ethylene action inhibitors. Wounded plant tissues accumulate many plant secondary products. DAHP synthase catalyzes the first reaction of the shikimate pathway that leads to the aromatic amino acids which are precursors of a number of secondary metabolites involved in plant defense and repair. Wounding Solanaceous tissues or treating parsley cells with fungal elicitor or light strongly induce DAHP synthase at the mRNA level. DAHP synthase mRNA accumulated coordinately with phenylalanine ammonia-lyase, potentially sharing regulatory factors which control primary and secondary metabolism. A tomato cDNA for DAHP synthase was cloned and sequenced. My data show that the tomato genome contains a single DAHP synthase gene which is induced by wounding but down regulated during fruit development and ripening, indicating environmental and developmental cues regulate the same gene. Transgenic potato plants were created to examine the expression of the DAHP synthase gene (shkA). The 5$\sp\prime$ region, flanking potato DAHP synthase coding sequences, was translationally fused to the reporter gene $\beta$-glucuronidase (GUS) and introduced into potato. Based on GUS activity, the shkA promoter conferred cell-specific and wound-inducible transgene expression similar to that of the endogenous DAHP synthase. However, the wound-induced accumulation of the endogenous DAHP synthase mRNA was inhibited by the expression of the introduced GUS transgene. This interaction suggests competition between endogenous and introduced homologous promoters for trans-acting transcription factors. Collectively, the data indicate that DAHP synthase is highly regulated and is an important control point for carbon flow through the shikimate pathway.

Degree

Ph.D.

Advisors

Handa, Purdue University.

Subject Area

Molecular biology|Botany

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