Departament de Biologia Vegetal, Facultat de Farmàcia, Universitat de València, 46010 València, Spain.
Estructura de Recerca Interdisciplinar en Biotecnologia i Biomedicina (ERI BIOTECMED), Universitat de València, 46100 Burjassot, Spain.
Plant Physiol. 2019 May;180(1):153-170. doi: 10.1104/pp.18.01549. Epub 2019 Feb 20.
Although the plant Phosphorylated Pathway of l-Ser Biosynthesis (PPSB) is essential for embryo and pollen development, and for root growth, its metabolic implications have not been fully investigated. A transcriptomics analysis of Arabidopsis () PPSB-deficient mutants at night, when PPSB activity is thought to be more important, suggested interaction with the sulfate assimilation process. Because sulfate assimilation occurs mainly in the light, we also investigated it in PPSB-deficient lines in the day. Key genes in the sulfate starvation response, such as the adenosine 5'phosphosulfate reductase genes, along with sulfate transporters, especially those involved in sulfate translocation in the plant, were induced in the PPSB-deficient lines. However, sulfate content was not reduced in these lines as compared with wild-type plants; besides the glutathione (GSH) steady-state levels in roots of PPSB-deficient lines were even higher than in wild type. This suggested that PPSB deficiency perturbs the sulfate assimilation process between tissues/organs. Alteration of thiol distribution in leaves from different developmental stages, and between aerial parts and roots in plants with reduced PPSB activity, provided evidence supporting this idea. Diminished PPSB activity caused an enhanced flux of S into thiol biosynthesis, especially in roots. GSH turnover also accelerated in the PPSB-deficient lines, supporting the notion that not only biosynthesis, but also transport and allocation, of thiols were perturbed in the PPSB mutants. Our results suggest that PPSB is required for sulfide assimilation in specific heterotrophic tissues and that a lack of PPSB activity perturbs sulfur homeostasis between photosynthetic and nonphotosynthetic tissues.
虽然植物 l-丝氨酸生物合成的磷酸化途径（PPSB）对于胚胎和花粉发育以及根生长至关重要，但它的代谢影响尚未得到充分研究。对拟南芥（）PPSB 缺陷突变体在夜间（据认为 PPSB 活性更为重要）的转录组学分析表明，其与硫酸盐同化过程相互作用。由于硫酸盐同化主要发生在光照下，我们还在 PPSB 缺陷型系中白天进行了研究。硫酸盐饥饿反应的关键基因，如腺苷 5'磷酸硫酸盐还原酶基因，以及硫酸盐转运体，特别是那些参与植物中硫酸盐转运的基因，在 PPSB 缺陷型系中被诱导。然而，与野生型植物相比，这些系中的硫酸盐含量并没有降低；此外，PPSB 缺陷型系的根中的谷胱甘肽（GSH）稳态水平甚至高于野生型。这表明 PPSB 缺陷会扰乱组织/器官之间的硫酸盐同化过程。PPSB 活性降低的叶片不同发育阶段以及植株地上部分和根部之间的巯基分布的改变，为这一观点提供了证据。减少的 PPSB 活性导致 S 流入巯基生物合成的通量增加，特别是在根部。PPSB 缺陷型系中的 GSH 周转率也加快，这支持了这样一种观点，即不仅是巯基的生物合成，而且还有运输和分配，在 PPSB 突变体中受到干扰。我们的结果表明，PPSB 是特定异养组织中硫化物同化所必需的，缺乏 PPSB 活性会扰乱光合和非光合组织之间的硫稳态。
