Molecular characterization of three differentially expressed members of the Camptotheca acuminata 3-hydroxy-3-methylglutaryl CoA reductase (HMGR) gene family

Camptotheca acuminata is a Chinese tree that produces the anti-cancer monoterpenoid indole alkaloid camptothecin (CPT). 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) supplies mevalonate for the terpenoid moiety of CPT and its hydroxylated derivative 10-hydroxycamptothecin (10-OH-CPT). We previously described the isolation of a gene encoding HMGR from C. acuminata (hmg1) and analyzed its expression in transgenic tobacco [6]. Here, we report on the isolation of genomic (hmg2) and cDNA (hmg3) clones representing two additional HMGR gene family members and characterize the expression of all three genes in C. acuminata. Transcript levels for two family members were highest in the shoot apex, dry seeds (hmg1), and bark (hmg3) which are the tissues containing the highest levels of CPT and IO-OH-CPT respectively. Levels of hmg3 mRNA also correlated with the accumulation of 10-OH-CPT during germination. In C. acuminata leaf disks, hmg1 mRNA increased in response to wounding, and this induction was suppressed by methyljasmonate (MeJA), in agreement with results previously obtained in transgenic tobacco [6]. In contrast, wounding and MeJA did not affect hmg2 or hmg3 transcript levels in C. acuminata. These results show that members of the C. acuminata HMGR gene family are differentially expressed in various tissues under different physiological conditions which may contribute to the regulation of monoterpenoid indole alkaloid synthesis in this species.