Zhao Le, Oyagbenro Richard, Feng Yiling, Xu Meimei, Peters Reuben J
Roy J. Carver Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50011 USA.
aBIOTECH. 2023 Jan 19;4(1):1-7. doi: 10.1007/s42994-022-00092-3. eCollection 2023 Mar.
Rice produces many diterpenoid phytoalexins and, reflecting the importance of these natural products in this important cereal crop plant, its genome contains three biosynthetic gene clusters () for such metabolism. The chromosome 4 () is largely associated with momilactone production, in part due to the presence of the initiating -copalyl diphosphate (CPP) synthase gene (). Oryzalexin S is also derived from -CPP. However, the relevant subsequently acting -stemarene synthase gene () is not located in the . Production of oryzalexin S further requires hydroxylation at carbons 2 and 19 (C2 and C19), presumably catalyzed by cytochrome P450 (CYP) monooxygenases. Here it is reported the closely related CYP99A2 and CYP99A3, whose genes are also found in the catalyze the necessary C19-hydroxylation, while the closely related CYP71Z21 and CYP71Z22, whose genes are found in the recently reported chromosome 7 (), catalyze subsequent hydroxylation at C2α. Thus, oryzalexin S biosynthesis utilizes two distinct , in a pathway cross-stitched together by . Notably, in contrast to the widely conserved , the is subspecies (ssp.) specific, being prevalent in ssp. japonica and only rarely found in the other major ssp. indica. Moreover, while the closely related -stemodene synthase was originally considered to be distinct from , it has now been reported to be a ssp. indica derived allele at the same genetic loci. Intriguingly, more detailed analysis indicates that is being replaced by (), suggesting introgression from ssp. indica to (sub)tropical japonica, with concurrent disappearance of oryzalexin S production.
The online version contains supplementary material available at 10.1007/s42994-022-00092-3.
水稻会产生多种二萜类植物抗毒素，鉴于这些天然产物在这种重要的谷类作物中的重要性，其基因组包含三个用于此类代谢的生物合成基因簇。4号染色体（）在很大程度上与稻瘟菌素的产生有关，部分原因是起始的牻牛儿基牻牛儿基二磷酸（CPP）合酶基因（）的存在。稻瘟菌素S也源自 -CPP。然而，相关的随后起作用的 -甜没药烯合酶基因（）并不位于该染色体上。稻瘟菌素S的产生还需要在碳2和19（C2和C19）处进行羟基化，推测是由细胞色素P450（CYP）单加氧酶催化的。在此报道了密切相关的CYP99A2和CYP99A3，它们的基因也在该染色体上，催化必要的C19羟基化，而密切相关的CYP71Z21和CYP71Z22，它们的基因在最近报道的7号染色体（）上，催化随后在C2α处的羟基化。因此，稻瘟菌素S的生物合成利用了两个不同的染色体，通过细胞色素P450单加氧酶将它们拼接在一条途径中。值得注意的是，与广泛保守的细胞色素P450单加氧酶不同，这种细胞色素P450单加氧酶是亚种特异性的，在粳稻亚种中普遍存在，而在另一个主要亚种籼稻中很少见。此外，虽然密切相关的 -异蒲勒醇合酶最初被认为与 -甜没药烯合酶不同，但现在已报道它是同一基因座上源自籼稻亚种的等位基因。有趣的是，更详细的分析表明 -甜没药烯合酶正在被 -异蒲勒醇合酶（）取代，这表明从籼稻亚种渗入到（亚热带）粳稻中，同时稻瘟菌素S的产生消失。
在线版本包含可在10.1007/s42994-022-00092-3获取的补充材料。
