Deficiency of Volatile Terpenoids in Gossypol-Free Glandless Cotton and Characterization of Terpene Synthases

Cotton plants accumulate large amount of gossypol derivate as phytoalexin against pathogens and herbivore insects in epidermal layers of roots and pigment glands of upland tissues. However, little is known about the metabolism of other volatile monoterpenes and sesquiterpenes, which may also play roles in plant interaction with biotic and abiotic environmental factors. By Gas Chromatography – Mass Spectrum (GC-MS) analysis, multiple monoterpenes (α-Pinene, β-Pinene and β-Myrcene) and sesquiterpenes (β-Caryophyllene, α-Humulene, β-Farnesene and α-Himachalene) were detected in upland tissues of cotton plants. When stimulated by mechanical wounding, Verticillium dahliae (Vde) elicitor and jasmonate, increased production of these terpenoids was observed. Interestingly, more than gossypol, all the volatile monoterpenes and sesquiterpenes were also deficient in the dominant glandless cotton tissues. By EST data mining combined with Rapid Amplification of cDNA Ends (RACE), full length cDNA of two terpene synthases, GhTPS1 and GhTPS2 were isolated. GhTPS1 was expressed constitutively throughout cotton plant, whereas GhTPS2 was specifically detected in leaves. Transcripts of both TPSs were strongly increased when stimulated by multiple treatments. In the glandless cotton plants, consistent with the deficiency of volatile terpenes, expression of GhTPS1 and GhTPS2, as well as other TPSs with partial mRNA sequences, were all decreased, like gossypol biosynthesis pathway genes. When expressed in E.coli, the recombinant GhTPS1 protein was able to convert FPP into β-caryophyllene and α-humulene at a ratio of 2:1, whereas GhTPS2 catalyze the production of several sesquiterpenes with guaia-1(10),11-diene as major. When transcriptional suppressed by Virus Induced Gene Silencing (VIGS), deficiency of corresponding sesquiterpenes in leaves were observed, suggesting GhTPS1 and GhTPS2 are major player of volatile sesquiterpene production in cotton plants.