Stemar‐13‐ene synthase, a diterpene cyclase involved in the biosynthesis of the phytoalexin oryzalexin S in rice

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Abstract
In suspension‐cultured rice cells, diterpenoid phytoalexins are produced in response to exogenously applied elicitors. We isolated a cDNA encoding a diterpene cyclase, OsDTC2, from suspension‐cultured rice cells treated with a chitin elicitor. The OsDTC2 cDNA was overexpressed in Escherichia coli as a fusion protein with glutathione S‐transferase, and the recombinant OsDTC2 was indicated to function as stemar‐13‐ene synthase that converted syn‐copalyl diphosphate to stemar‐13‐ene, a putative diterpene hydrocarbon precursor of the phytoalexin oryzalexin S. The level of OsDTC2 mRNA in suspension‐cultured rice cells began to increase 3 h after addition of the elicitor and reached the maximum after 8 h. The expression of OsDTC2 was also induced in UV‐irradiated rice leaves. In addition, we indicated that stemar‐13‐ene accumulated in the chitin‐elicited suspension‐cultured rice cells and the UV‐irradiated rice leaves.