Weers Tristan, Feng Yiling, Peters Reuben J
Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, Iowa State University, Ames, IA, 50011, USA.
Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, Iowa State University, Ames, IA, 50011, USA.
Phytochemistry. 2025 Aug 8;240:114634. doi: 10.1016/j.phytochem.2025.114634.
The widely cultivated Asian rice (Oryza sativa) produces a variety of physiologically relevant diterpenoid products, which range in effect from the phytohormone gibberellin, derived from ent-kaurene, to phytoalexins such as the momilactones, derived from syn-pimara-7,15-diene. Previous reports have shown functional variation in the kaurene synthase-like (KSL) genes responsible for synthesizing diterpene precursors to more specialized metabolites, leading to the creation of distinct diterpenoids from allelomorphic genes. Here is reported the product of two previously discovered but uncharacterized alleles of the unusual KSLX, representing a cross between (fusion of) the tandem pair KSL8-KSL9p found in most cultivars. The previously characterized allele (KSLXo) was reported to act on syn-copalyl pyrophosphate (syn-CPP) to produce syn-abieta-7,12-diene, precursor to the phytoalexin oryzalactone. However, at least one other functionally distinct allele was reported from the O. sativa pan-genome (KSLXn), along with another phylogenetically distinct allele found in Oryza barthii (KSLXb), but these were not further characterized. Here both KSLXn and KSLXb were found to selectively react with syn-CPP and produce syn-pimara-9(11),15-diene, a novel diterpene in rice. Additionally, evolution of this locus was investigated, with KSLXb hypothesized to be a functional KSL9. The striking complexity of this locus, which includes distinct composition (KSL8-KSL9(p) or KSLX) as well as allelomorphism of both KSL8 and KSLX, suggests it is subject to balancing selection, consistent with the competing pressures exerted on phytoalexin biosynthesis. Regardless, the studies reported here clarify this additional example of allelomorphic variation in the rice KSL family, providing insight into the rice pan-genomic diterpenoid arsenal.
广泛种植的亚洲水稻（Oryza sativa）能产生多种具有生理相关性的二萜类产物，其作用范围从源自贝壳杉烯的植物激素赤霉素，到源自顺式-海松-7,15-二烯的植保素如稻瘟菌素。先前的报道显示，负责合成二萜前体以生成更特殊代谢产物的贝壳杉烯合酶样（KSL）基因存在功能变异，导致等位基因产生不同的二萜类化合物。本文报道了两个先前发现但未表征的不寻常KSLX等位基因的产物，它们代表了大多数品种中串联对KSL8 - KSL9p的杂交（融合）。先前表征的等位基因（KSLXo）据报道作用于顺式-柯巴基焦磷酸（syn-CPP）以产生顺式-阿替-7,12-二烯，即植保素稻瘟内酯的前体。然而，从水稻泛基因组中报道了至少另一个功能不同的等位基因（KSLXn），以及在野生稻（Oryza barthii）中发现的另一个系统发育上不同的等位基因（KSLXb），但这些未进一步表征。在这里发现KSLXn和KSLXb都能选择性地与顺式-CPP反应并产生顺式-海松-9(11),15-二烯，这是水稻中的一种新型二萜。此外，还研究了该基因座的进化，推测KSLXb是一个功能性KSL9。该基因座的显著复杂性，包括不同的组成（KSL8 - KSL9(p)或KSLX）以及KSL8和KSLX的等位基因多态性，表明它受到平衡选择，这与施加在植保素生物合成上的竞争压力一致。无论如何，本文报道的研究阐明了水稻KSL家族中等位基因变异的这一额外例子，为水稻泛基因组二萜类物质库提供了见解。
