Faculty of Biology II, University of Freiburg, Schänzlestr., Freiburg, Germany.
Planta. 2010 Oct;232(5):1251-62. doi: 10.1007/s00425-010-1250-6. Epub 2010 Aug 25.
Abiotic stress stimuli induce the increased synthesis of abscisic acid (ABA), which is generated through the cleavage of xanthophyll precursors. To cope with the increased xanthophyll demand, maize and rice contain a third stress-induced gene copy, coding for phytoene synthase (PSY), which catalyzes the first carotenoid-specific reaction in the pathway. To investigate whether this specific response extends beyond the Poaceae, cassava was analyzed, an important tropical crop known for its drought tolerance. We also found three PSY genes in cassava, one of which (MePSY3) forms a separate branch with the stress-specific Poaceae homologs. However, MePSY3 transcripts were virtually absent in all tissues investigated and did not change upon abiotic stress treatment. In contrast, the two remaining PSY genes contributed differentially to carotenoid biosynthesis in leaves, roots, and flower organs and responded towards drought and salt-stress conditions. Detailed analyses of PSY and 9-cis-epoxycarotenoid cleavage dioxygenase (MeNCED) expression and resulting ABA levels revealed MePSY1 as the main stress-responsive paralog. In the presence of high carotenoid levels in leaves, MePSY1 appeared to support, but not to be rate-limiting for ABA formation; MeNCED represented the main driver. The inverse situation was found in roots where carotenoid levels are low. Moreover, ABA formation and the relative induction kinetics showed discrimination between drought and salt stress. Compared to rice as a drought-intolerant species, the drought response in cassava followed a different kinetic regime. The difference is thought to represent a component contributing to the large differences in the adaptation towards water supply.
非生物胁迫刺激会诱导脱落酸（ABA）的合成增加，ABA 是通过叶黄素前体的裂解产生的。为了应对叶黄素需求的增加，玉米和水稻含有第三个应激诱导的基因拷贝，编码八氢番茄红素合酶（PSY），它催化该途径中第一个类胡萝卜素特异性反应。为了研究这种特定的反应是否超出了禾本科植物，我们分析了木薯，木薯是一种重要的热带作物，以其耐旱性而闻名。我们还在木薯中发现了三个 PSY 基因，其中一个（MePSY3）与应激特异性禾本科同源物形成一个单独的分支。然而，MePSY3 的转录本在所有研究的组织中几乎不存在，并且在非生物胁迫处理后没有变化。相比之下，其余两个 PSY 基因在叶片、根和花器官中的类胡萝卜素生物合成中表现出不同的贡献，并对干旱和盐胁迫条件作出响应。PSY 和 9-顺式-环氧类胡萝卜素双加氧酶（MeNCED）表达和 ABA 水平的详细分析表明，MePSY1 是主要的应激响应基因。在叶片中存在高类胡萝卜素水平的情况下，MePSY1 似乎支持而不是限制 ABA 的形成；MeNCED 是主要的驱动因素。在根中则相反，根中类胡萝卜素水平较低。此外，ABA 的形成和相对诱导动力学显示出对干旱和盐胁迫的区分。与作为耐旱性较差的物种的水稻相比，木薯的干旱响应遵循不同的动力学模式。这种差异被认为是对供水适应差异的一个组成部分。
