Gibberellins (GAs) are diterpenoid hormones with a variety of roles in vascular plant growth and development ( Sun, 2011). Thus, these results clarify not only gibberellin phytohormone, but also diterpenoid phytoalexin biosynthesis in this important cereal crop plant. On the other hand, the expression of all three of these genes is inducible, suggesting a role in more specialized metabolism, such as that of the kauralexins. ![]() Consistent with the closer phylogenetic relationship of ZmKS元 with previously identified KSs from cereals, only transcription of this gene is affected in d5 plants. Here it is reported that all three genes encode enzymes that are targeted to the plastid in planta, where diterpenoid biosynthesis is initiated, and which all readily catalyze the production of ent-kaurene. Although one of these, ZmTPS1, has been previously reported to encode a sesquiterpene synthase, and both ZmTPS1 and that encoded by the third gene, ZmKSL5, have lost the N-terminal γ-domain prototypically associated with KS(L)s, all three genes fall within the KS(L) or TPS-e subfamily. Intriguingly, this forms part of a tandem array with two other terpene synthases ( TPSs). The relevant genetic lesion has been previously mapped, and was found here to correlate with the location of the KS-like gene ZmKS元. The maize gibberellin-deficient dwarf-5 ( d5) mutant has been associated with a loss of KS activity. However, no ent-kaurene synthases ( KSs) have been identified from maize. ![]() While most commonly associated with its role in gibberellin phytohormone biosynthesis, ent-kaurene also serves as an intermediate in more specialized diterpenoid metabolism, as exemplified by the more than 800 known derived natural products.
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