Evolutionary Analysis of (+)-δ-Cadinene Synthases and 8-hydroxy-(+)-δ Cadinene Synthases in Gossypium spp

Cotton plants accumulate gossypol and related sesquiterpenoids which function as the major phytoalexin but limit the use of cottonseeds. We have isolated two enzymes of gossypol biosynthesis pathway, including (+)-δ-cadinene synthase (CDN, the sesquiterpene synthase) and 8-hydroxy-(+)-δ cadinene synthase (CYP706B1, P450 monooxygenase). To better understand the evolutionary history of gossypol formation in gossypium species, a genome-wide analysis of terpene synthases and P450s from 15 representative species was carried out. A total of 591 terpene synthases and 159 CYP706 family members were identified in these plants. We found both CDNs and CYP706B1 are newly evolved enzymes and existed specifically in gossypium species. Species-specific gene duplications, caused mainly by tandem duplication and segmental duplication, led to the expansion of CDN genes in gossypium species. Based on nucleic acid and amino acid sequence identities, CDNs can be divided into five (A-E) subfamilies. Of these, the CDN-E subfamily seems to be the prototype since it is closest to CDNs in T. cacao. Of the hundreds of P450s found in diploid and allotetraploid cotton genomes, CYP71 family was greatly specifically. Interestingly, members of the CYP706B subfamily are found only in Malvales, including cotton (Gossypium spp.) and cacao (Theobroma cacao), suggesting a role of P450s in the evolution of plant specialized metabolites.