Perreca Erica, Rohwer Johann, González-Cabanelas Diego, Loreto Francesco, Schmidt Axel, Gershenzon Jonathan, Wright Louwrance Peter
Department of Biochemistry, Max Planck Institute for Chemical Ecology, Jena, Germany.
Laboratory for Molecular Systems Biology, Department of Biochemistry, Stellenbosch University, Stellenbosch, South Africa.
Front Plant Sci. 2020 Oct 9;11:546295. doi: 10.3389/fpls.2020.546295. eCollection 2020.
The methylerythritol 4-phosphate (MEP) pathway of isoprenoid biosynthesis produces chlorophyll side chains and compounds that function in resistance to abiotic stresses, including carotenoids, and isoprene. Thus we investigated the effects of moderate and severe drought on MEP pathway function in the conifer , a boreal species at risk under global warming trends. Although moderate drought treatment reduced the photosynthetic rate by over 70%, metabolic flux through the MEP pathway was reduced by only 37%. The activity of the putative rate-limiting step, 1-deoxy-D-xylulose-5-phosphate synthase (DXS), was also reduced by about 50%, supporting the key role of this enzyme in regulating pathway metabolic flux. However, under severe drought, as flux declined below detectable levels, DXS activity showed no significant decrease, indicating a much-reduced role in controlling flux under these conditions. Both MEP pathway intermediates and the MEP pathway product isoprene incorporate administered CO to high levels (75-85%) under well-watered control conditions indicating a close connection to photosynthesis. However, this incorporation declined precipitously under drought, demonstrating exploitation of alternative carbon sources. Despite the reductions in MEP pathway flux and intermediate pools, there was no detectable decline in most major MEP pathway products under drought (except for violaxanthin under moderate and severe stress and isoprene under severe stress) suggesting that the pathway is somehow buffered against this stress. The resilience of the MEP pathway under drought may be a consequence of the importance of the metabolites formed under these conditions.
类异戊二烯生物合成的甲基赤藓糖醇4-磷酸（MEP）途径产生叶绿素侧链以及在抗非生物胁迫中起作用的化合物，包括类胡萝卜素和异戊二烯。因此，我们研究了中度和重度干旱对针叶树MEP途径功能的影响，针叶树是一种在全球变暖趋势下面临风险的北方物种。尽管中度干旱处理使光合速率降低了70%以上，但通过MEP途径的代谢通量仅降低了37%。假定的限速步骤1-脱氧-D-木酮糖-5-磷酸合酶（DXS）的活性也降低了约50%，这支持了该酶在调节途径代谢通量中的关键作用。然而，在严重干旱下，随着通量下降到可检测水平以下，DXS活性没有显著下降，表明在这些条件下其在控制通量方面的作用大大降低。在水分充足的对照条件下，MEP途径中间体和MEP途径产物异戊二烯都能将施用的CO大量掺入（75-85%），这表明与光合作用密切相关。然而，在干旱条件下这种掺入急剧下降，表明利用了替代碳源。尽管MEP途径通量和中间产物库减少，但在干旱条件下大多数主要MEP途径产物没有可检测到的下降（中度和重度胁迫下的紫黄质以及重度胁迫下的异戊二烯除外），这表明该途径在某种程度上对这种胁迫具有缓冲作用。干旱条件下MEP途径的恢复力可能是这些条件下形成的代谢物重要性的结果。
