Isolation of an elicitor-stimulated 5-epi-aristolochene synthase gene (gPEAS1) from chili pepper (Capsicum annuum)

Phytoalexins play an important role in the inducible defense responses of p lants against diseases caused by fungi. Some enzymes, involved in the respe ctive biosynthetic pathways, catalyze key steps. Farnesyl pyrophosphate (FP P) is a key intermediate in the biosynthesis of terpenes. It may be convert ed into several cyclic and some acyclic sesquiterpenic derivatives, sterol precursors, or to geranylgeranyl pyrophosphate according to the requirement s of the plant cells. Specific cyclization reactions of FPP are catalyzed b y particular sesquiterpene cyclases. The 5-epi-aristolochene synthase (EAS) enzyme of tobacco (Nicotiana tabacum) and pepper (Capsicum annuum) produce the 5-epi-aristolochene, which is the immediate precursor of the bicyclic phytoalexin capsidiol. Oligonucleotides homologous to 3'-end specific regio ns of tobacco and Hyoscyamus muticus inducible sesquiterpene cyclase genes were used with the system for rapid amplification of cDNA ends (3'-RACE) te chnique to prepare pepper EAS-cDNA fragments (PEAS-cDNA). Three specific PE AS-cDNAs were isolated (PEAS1, PEAS18, and PEAS55), Northern blots of total RNA samples from pepper plant tissues challenged with cellulase or Phytoph thora capsici showed different expression levels of the respective transcri pts. PEAS1 was used to identify the corresponding elicitor-stimulated gene (gPEAS1). The nucleotide sequence of the proposed gPEAS1 promoter showed pu tative stimuli- and tissue-specific responsive elements. A pepper 5-epi-ari stolochene synthase gene family of 5-8 members was demonstrated by Southern blot.