Department of Molecular Biotechnology and Kumho Life Science Laboratory, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 61186, Republic of Korea.
Department of Molecular Biotechnology and Kumho Life Science Laboratory, College of Agriculture and Life Sciences, Chonnam National University, Gwangju 61186, Republic of Korea.
Bioorg Chem. 2023 Feb;131:106285. doi: 10.1016/j.bioorg.2022.106285. Epub 2022 Nov 24.
The peroxygenase pathway plays pivotal roles in plant responses to oxidative stress and other environmental stressors. Analysis of a network of co-expressed stress-regulated rice genes demonstrated that expression of OsPXG9 is negatively correlated with expression of genes involved in jasmonic acid biosynthesis. DNA sequence analysis and structure/function studies reveal that OsPXG9 is a caleosin-like peroxygenase with amphipathic α-helices that localizes to lipid droplets in rice cells. Enzymatic studies demonstrate that 12-epoxidation is slightly more favorable with 9(S)-hydroperoxyoctadecatrienoic acid than with 9(S)-hydroperoxyoctadecadienoic acid as substrate. The products of 12-epoxidation are labile, and the epoxide ring is hydrolytically cleaved into corresponding trihydroxy compounds. On the other hand, OsPXG9 catalyzed 15-epoxidation of 13(S)-hydroperoxyoctadecatrienoic acid generates a relatively stable epoxide product. Therefore, the regiospecific 12- or 15-epoxidation catalyzed by OsPXG9 strongly depends on activation of the 9- or 13- peroxygenase reaction pathways, with their respective preferred substrates. The relative abundance of products in the 9-PXG and 13-PXG pathways suggest that the 12-epoxidation involves intramolecular oxygen transfer while the 15-epoxidation can proceed via intramolecular or intermolecular oxygen transfer. Expression of OsPXG9 is up-regulated by abiotic stimuli such as drought and salt stress, but it is down-regulated by biotic stimuli such as flagellin 22 and salicylic acid. The results suggest that the primary function of OsPXG9 is to modulate the level of lipid peroxides to facilitate effective defense responses to abiotic and biotic stressors.
过氧化物酶体途径在植物应对氧化应激和其他环境胁迫的反应中发挥着关键作用。对一组共同表达的应激调节水稻基因的网络分析表明，OsPXG9 的表达与茉莉酸生物合成相关基因的表达呈负相关。DNA 序列分析和结构/功能研究表明，OsPXG9 是一种钙蛋白酶样过氧化物酶，具有两亲性α-螺旋，定位于水稻细胞中的脂滴中。酶学研究表明，与 9(S)-羟基过氧十八碳二烯酸相比，12-环氧化反应对 9(S)-羟基过氧十八碳三烯酸更有利。12-环氧化的产物不稳定，环氧化物环会水解成相应的三羟基化合物。另一方面，OsPXG9 催化 13(S)-羟基过氧十八碳三烯酸的 15-环氧化生成相对稳定的环氧化产物。因此，OsPXG9 催化的 12-或 15-环氧化的区域特异性强烈依赖于 9-或 13-过氧化物酶反应途径的激活，以及它们各自的优选底物。9-PXG 和 13-PXG 途径中产物的相对丰度表明，12-环氧化涉及分子内氧转移，而 15-环氧化可以通过分子内或分子间氧转移进行。OsPXG9 的表达受非生物胁迫如干旱和盐胁迫的诱导上调，但受生物胁迫如鞭毛蛋白 22 和水杨酸的诱导下调。结果表明，OsPXG9 的主要功能是调节脂质过氧化物的水平，以促进对生物和非生物胁迫因子的有效防御反应。
