Expression of a 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase Gene from Camptotheca acuminata Is Differentially Regulated by Wounding and Methyl Jasmonate

Abstract

We have isolated a gene, hmgl, for 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMCR) from Camptotheca acuminata, aChinese tree that produces the anti-cancer monoterpenoid indole alkaloid camptothecin (CPT). HMCR supplies mevalonate for the synthesis of the terpenoid component of CPT as well as for the formation of many other primary and secondary metabolites. In Camptotheca, hmgl transcripts were detected only in young seedlings and not in vegetative organs of older plants. Regulation of the hmgl promoter was studied in transgenic tobacco using three translational fusions (-1678, -1 107, -165) with the B-glucuronidase (GUS) reporter gene. Histochemical analysis of plants containing each of the three promoter fusions showed similar developmental and spatial expression patterns. In vegetative tissues, CUS staining was localized to the epidermis of young leaves and stems, particularly in glandular trichomes. Roots showed intense staining in the cortical tissues in the elongation zone and light staining in the cortex of mature roots. hmgl::CUS expression was also observed in sepals, petals, pistils, and stamens of developing flowers, with darkest staining in the ovary wall, ovules, stigmas, and pollen. Leaf discs from plants containing each of the translational fusions showed a 15-to 20-fold wound induction of hmgl::CUS expression over 72 h; however, this increase in CUS activity was completely suppressed by treatment with methyl jasmonate. Taken together, these data show that a 165-bp fragment of Camptotheca hmgl promoter is sufficient to confer developmental regulation as well as wound induction and methyl jasmonate suppression of GUS expression in transgenic tobacco.

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

“…We showed that the Arabidopsis HMGP gene promoter is not induced in wounded leaves of transgenic tobacco plants containing construct (-857/+64)HMGP-GUS. Under similar experimental conditions, the promoter of the C. acuminata hmgl gene was highly induced in transgenic tobacco plants (Burnett et al, 1993). Our results suggest that the Arabidopsis HMGP gene is not involved in the synthesis of specific isoprenoids in response to wounding.…”

“…Specific potato HMGR genes are differentially expressed in response to wounding and pathogen challenge (Yang et al, 1991;Choi et al, 1992). lnduction of the Camptotheca acuminata hmgl gene by wounding has been reported in transgenic tobacco plants (Burnett et al, 1993). Arabidopsis contains two differentially expressed HMGR genes, HMGl and HMGP.…”

Terpenoid metabolism.

“…Severa1 feedback regulatory mechanisms control transcription of the reductase gene, and its catalytic activity is modulated by both covalent modification and noncovalent interactions (Goldstein and Brown, 1990). In contrast, plants, which produce much more diverse products from the mevalonate pathway in various tissues and organelles, contain multiple, differentially regulated genes for HMG-COA reductase (Narita and Gruissem, 1989;Yang et al, 1991;Choi et al, 1992;Chye et al, 1992;Genschik et al, 1992;Burnett et al, 1993;Enjuto et al, 1994). Different reductase genes are expressed in different parts of the plant (Chye et al, 1992;Genschik et al, 1992;Enjuto et al, 1994), at different stages of development (Narita and Gruissem, 1989), and in response to various stresses (Yang et al, 1991;Choi et al, 1992;Genschik et al, 1992).…”

Selective Enhancement of Scopadulcic Acid B Production in the Cultured Tissues of Scoparia dulcis by Methyl Jasmonate

“…It was shown that wounding of plant tissues induced hmg1 gene that encodes HMGR enzymes involved in the biosynthesis of phytosterols and its induction was suppressed by elicitors in a potato 24) and methyl jasmonate in Camptotheca acuminata. 25) These findings might explain the decrease in the content of b-sitosterol in the tissues treated with MeJA. In our previous communication, the involvement of 1-deoxy-D-xylulose 5-phosphate (DOXP) pathway, so called mevalonate-independent pathway, in the biosynthesis of SDB and phytol was suggested, while b-sitosterol was indicated to be biosynthesized via the mevalonate pathway.…”