Elucidation of Gossypol Biosynthesis Pathway

Cotton plants accumulate gossypol and related sesquiterpene aldehydes, which function as phytoalexins against pathogens and herbivores. Till now progress has been made in characterization of gossypol biosynthetic pathway, and several enzymes catalyzing early steps of the pathway have been cloned, including farnesyl pyrophosphate synthase (FPS), (+)-σ-cadinene synthase (CDN) and the P450 monooxygenase CYP706B1.

To elucidate the downstream steps, we performed comparative transcriptome analysis of glanded and glandless cotton plants, which resulted in isolation of genes that are preferentially or specifically expressed in the glanded cultivar. Of these, one encodes a P450 monooxygenase (CQ1) and another encodes a short chain alcohol dehydrogenase (CQ2), and both were strongly induced by fungal elicitor. In vitro assays with recombinant proteins showed that CQ2 was able to convert the 8-hydroxy-σ-cadinene into a new compound (A), which was further hydroxylated by CQ1. Moreover, CQ1 also showed the hydroxylation activity towards (+)-σ-cadinene, leading to 8-hydroxy-σ-cadinene. When either CQ1 or CQ2expression was down-regulated by virus induced gene silencing (VIGS), content of gossypol was decreased significantly, and increased accumulation of intermediates was detected. These data indicate that CQ1 and CQ2 are gossypol biosynthesis pathway enzymes that function downstream of CDN and CYP706B1.

With recent and continuous release of cotton genome data, we performed analysis of gene families of the enzymes involved in gossypol biosynthesis, and some of the results will be discussed during presentation.