Samuilov Sladjana, Rademacher Nadine, Brilhaus Dominik, Flachbart Samantha, Arab Leila, Kopriva Stanislav, Weber Andreas P M, Mettler-Altmann Tabea, Rennenberg Heinz
Chair of Tree Physiology, Institute of Forest Sciences, Faculty of Environment and Natural Resources, University of Freiburg, Freiburg, Germany.
Institute of Plant Biochemistry, Cluster of Excellence on Plant Sciences, Heinrich Heine University, Düsseldorf, Germany.
Front Plant Sci. 2018 Dec 11;9:1830. doi: 10.3389/fpls.2018.01830. eCollection 2018.
The aim of present study was to elucidate the significance of the phosphorylated pathway of Ser production for Cys biosynthesis in leaves at day and night and upon cadmium (Cd) exposure. For this purpose, wildtype plants as control and its mutant knocked-down in phosphoserine phosphatase () were used to test if (i) photorespiratory Ser is the dominant precursor of Cys synthesis in autotrophic tissue in the light, (ii) the phosphorylated pathway of Ser production can take over Ser biosynthesis in leaves at night, and (iii) Cd exposure stimulates Cys and glutathione (GSH) biosynthesis and effects the crosstalk of S and N metabolism, irrespective of the Ser source. Glycine (Gly) and Ser contents were not affected by reduction of the transcript level confirming that the photorespiratory pathway is the main route of Ser synthesis. The reduction of the transcript level in the mutant did not affect day/night regulation of sulfur fluxes while day/night fluctuation of sulfur metabolite amounts were no longer observed, presumably due to slower turnover of sulfur metabolites in the mutant. Enhanced contents of non-protein thiols in both genotypes and of GSH only in the mutant were observed upon Cd treatment. Mutation of the phosphorylated pathway of Ser biosynthesis caused an accumulation of alanine, aspartate, lysine and a decrease of branched-chain amino acids. Knock-down of the gene induced additional defense mechanisms against Cd toxicity that differ from those of WT plants.
本研究的目的是阐明丝氨酸（Ser）磷酸化途径在白天和夜晚以及镉（Cd）暴露时对叶片中半胱氨酸（Cys）生物合成的意义。为此，使用野生型植物作为对照及其丝氨酸磷酸酶（）基因敲除突变体来测试：（i）光呼吸丝氨酸是否是光下自养组织中半胱氨酸合成的主要前体；（ii）丝氨酸磷酸化途径是否能在夜间接管叶片中的丝氨酸生物合成；（iii）镉暴露是否会刺激半胱氨酸和谷胱甘肽（GSH）的生物合成，并影响硫和氮代谢的相互作用，而不考虑丝氨酸来源。甘氨酸（Gly）和丝氨酸含量不受转录水平降低的影响，这证实了光呼吸途径是丝氨酸合成的主要途径。突变体中转录水平的降低并不影响硫通量的昼夜调节，而硫代谢物量的昼夜波动不再被观察到，这可能是由于突变体中硫代谢物的周转较慢。镉处理后，两种基因型的非蛋白硫醇含量均增加，而仅在突变体中观察到谷胱甘肽含量增加。丝氨酸生物合成磷酸化途径的突变导致丙氨酸、天冬氨酸、赖氨酸的积累以及支链氨基酸的减少。基因敲除诱导了针对镉毒性的额外防御机制，这与野生型植物不同。
