Involvement of 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase in the Regulation of Sesquiterpenoid Phytoalexin Synthesis in Potato

Abstract

The importance of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase) in the regulation of sesquiterpenoid phytoalexin accumulation in potato (Solanum tuberosum L. cv Kennebec) was examined. Wounding of potato tubers produced a large temporary increase in HMG-CoA reductase activity of the microsomal and organelle fractions. Treatment of wounded tuber tissue with the sesquiterpenoid phytoalexin elicitor arachidonic acid further increased and prolonged the HMG-CoA reductase activity in the microsomal but not the organelle fraction. Incubation of elicitor-treated tuber tissue in white light reduced organelle and microsomal HMG-CoA reductase activity to 50% and 10%, respectively, of the activity of tissues held in darkness. Constant light also reduced overall phytoalexin accumulation 58% by greatly reducing levels of lubimin. Rishitin accumulation was not significantly altered by light. Application of nanomolar amounts of mevinolin, a highly specific inhibitor of HMG-CoA reductase, to elicitor-treated tuber tissue produced a large decline in lubimin accumulation and did not markedly alter rishitin accumulation. These results indicate that HMG-CoA reductase has a role in the complex regulation of sesquiterpenoid phytoalexin accumulation in potato.

Induction of Sesquiterpene Cyclase and Suppression of Squalene Synthetase Activities in Plant Cell Cultures Treated with Fungal Elicitor

“…Yet, those studies were prompted, in part, by anticipating a corollary between the role HMGR plays in regulating isoprenoid metabolism in mammalian cells to that of plants. The current results, along with previous results showing the inhibition of sesquiterprenoid production by mevinolin (9, 19), indicate that, while HMGR activity is undoubtedly required for the synthesis of sesquiterpenoids, more stringent regulation occurs by a modulation of the branch point enzymes as well as by other means. In the present study, induction of HMGR activity was rapid and transient, and had returned to control levels by the time the sesquiterpenoid biosynthetic rate was maximum (6-9 h postelicitor addition).…”

“…We, like others (19,21), previously correlated the de novo synthesis of the sesquiterpenoids by elicitor-treated cells with a transient induction of HMGR activity (9). Yet, those studies were prompted, in part, by anticipating a corollary between the role HMGR plays in regulating isoprenoid metabolism in mammalian cells to that of plants.…”

Expression of the Arabidopsis HMG2 gene, encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase, is restricted to meristematic and floral tissues.

“…Some of these metabolic changes have been correlated with changes in HMGR activity (Stermer and Bostock, 1987;Chapell et al, 1991) or differential expression of specific HMGR genes (Stermer et al, 1991;Yang et al, 1991;Choi et al, 1992;Cramer et al, 1993). We showed that the Arabidopsis HMGP gene promoter is not induced in wounded leaves of transgenic tobacco plants containing construct (-857/+64)HMGP-GUS.…”

Purification and Characterization of an Inducible Sesquiterpene Cyclase from Elicitor-Treated Tobacco Cell Suspension Cultures

“…Previous work by ourselves (9,31) and others (26,28) related the accumulation of sesquiterpenoids with the induction of 3-hydroxy-3-methylglutaryl CoA reductase, HMGR,3 a key regulatory step for isoprenoid metabolism in mammals (8). For example, addition offungal cell wall fragments to tobacco cell suspension cultures resulted in the de novo synthesis and accumulation ofextracellular sesquiterpenoids, including capsidiol (9).…”