Cloning and Heterologous Expression of a Second (+)-δ-Cadinene Synthase from Gossypium arboreum

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Abstract
Screening of a Gossypium arboreum L. cv. Nanking cDNA library resulted in the identification and cloning of a second (+)-δ-cadinene synthase. A probe for the screens was prepared by PCR using primers based on conserved sequences in farnesyl diphosphate cyclases and genomic DNA as a template. This second cDNA clone encodes a protein that is 80% identical to the recently described (+)-δ-cadinene synthases CAD1-C1 and C14 from G. arboreum and maintains a significant degree of homology to the other known mono-, sesqui-, and diterpene synthases. As in the case of CAD1-C1 (+)-δ-cadinene synthase from cultured cotton cells, the synthesis of the second CAD1-A mRNA was induced by treatment of cotton cell suspension cultures with a partially purified elicitor preparation from the phytopathogenic fungus Verticillium dahliae. Expression of CAD1-A mRNA was quantitated with reverse transcription PCR and showed that CAD1-A mRNA was maximally increased 8-fold, 6 h after addition of elicitor. Heterologous expression of this second cDNA produced a 64 kD protein that catalyzed the cyclization of farnesyl diphosphate to (+)-δ-cadinene, the identical product produced by CAD1-C1. The steady-state kinetic parameters of CAD1-A were similar to CAD1-C, showing a Km of 7 mM farnesyl diphosphate and kcat of 0.039 s-1 at 30 °C. However, the optimal pH and Mg2+ concentration for CAD1-A activity were significantly higher than those observed for CAD1-C.