Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570, Japan.
Tsukuba Research & Technology Center, SDS Biotech K.K., Tsukuba, 300-2646, Japan.
Plant Physiol. 2021 Oct 5;187(2):816-828. doi: 10.1093/plphys/kiab293.
The rice (Oryza sativa) 2-oxoglutarate (2OG)/Fe(II)-dependent dioxygenase HIS1 mediates the catalytic inactivation of five distinct β-triketone herbicides (bTHs). By assessing the effects of plant growth regulators on HIS1 enzyme function, we found that HIS1 mediates the hydroxylation of trinexapac-ethyl (TE) in the presence of Fe2+ and 2OG. TE blocks gibberellin biosynthesis, and we observed that its addition to culture medium induced growth retardation of rice seedlings in a concentration-dependent manner. Similar treatment with hydroxylated TE revealed that hydroxylation greatly attenuated the inhibitory effect of TE on plant growth. Forced expression of HIS1 in a rice his1 mutant also reduced its sensitivity to TE compared with that of the nontransformant. These results indicate that HIS1 metabolizes TE and thereby markedly reduces its ability to slow plant growth. Furthermore, analysis of five rice HIS1-like (HSL) proteins revealed that OsHSL2 and OsHSL4 also metabolize TE in vitro. HSLs from wheat (Triticum aestivum) and barley (Hordeum vulgare) also showed such activity. In contrast, OsHSL1, which shares the highest amino acid sequence identity with HIS1 and metabolizes the bTH tefuryltrione, did not manifest TE-metabolizing activity. Site-directed mutagenesis of OsHSL1 informed by structural models showed that substitution of three amino acids with the corresponding residues of HIS1 conferred TE-metabolizing activity similar to that of HIS1. Our results thus reveal a catalytic promiscuity of HIS1 and its related enzymes that support xenobiotic metabolism in plants.
水稻 2-氧戊二酸（2OG）/Fe（II）依赖性双加氧酶 HIS1 介导五种不同的β-三酮类除草剂（bTHs）的催化失活。通过评估植物生长调节剂对 HIS1 酶功能的影响，我们发现 HIS1 在 Fe2+和 2OG 的存在下介导 trinexapac-ethyl（TE）的羟化。TE 阻断赤霉素生物合成，我们观察到其添加到培养基中以浓度依赖的方式诱导水稻幼苗生长迟缓。用羟化 TE 进行类似处理表明，羟化大大减弱了 TE 对植物生长的抑制作用。在水稻 his1 突变体中强制表达 HIS1 也降低了其对 TE 的敏感性，与非转化体相比。这些结果表明 HIS1 代谢 TE，从而显著降低其减缓植物生长的能力。此外，对五个水稻 HIS1 样（HSL）蛋白的分析表明，OsHSL2 和 OsHSL4 也在体外代谢 TE。来自小麦（Triticum aestivum）和大麦（Hordeum vulgare）的 HSL 也表现出这种活性。相比之下，与 HIS1 共享最高氨基酸序列同一性并代谢 bTH tefuryltrione 的 OsHSL1 没有表现出 TE 代谢活性。基于结构模型的 OsHSL1 定点突变表明，用 HIS1 的相应残基取代三个氨基酸赋予了与 HIS1 相似的 TE 代谢活性。因此，我们的结果揭示了 HIS1 及其相关酶的催化多功能性，支持植物中外源化合物的代谢。
