Repression of CYSTATHIONINE γ-SYNTHASE in Seeds Recruits the S-Methylmethionine Cycle
Repression of CYSTATHIONINE γ-SYNTHASE in Seeds Recruits the S-Methylmethionine Cycle
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DOI：
10.1104/pp.17.00579
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发表时间：
2017-07-01
期刊：
影响因子：
7.4
通讯作者：
Amir, Rachel
中科院分区：
文献类型：
--
作者：
Cohen, Hagai;Hacham, Yael;Amir, Rachel
S-甲硫氨酸(SMM)参与种子蛋氨酸(Met)代谢。为了进一步揭示其功能，我们已经获得了Met的主要调节酶--胱硫醚-γ-合成酶(AtCGS)的低转录表达的转基因拟南芥(Arabiopsis Thaliana)RNA干扰(RNAi)种子。出乎意料的是，这些种子通过一种尚不清楚的机制，比对照种子积累了显著更高水平的Met。在这里，转录和代谢分析，结合同位素标记的[C-13]SMM和[C-13]Met的喂养实验，使我们能够揭示RNAi植物莲座叶中合成的SMM对其发育后期种子中Met的积累有显著贡献。种子特异性的AtCGS在RNAi种子中的抑制触发了在莲座叶的SMM循环中操作的基因的诱导，导致SMM向种子的运输增加，在种子中检测到较高的SMM到Met的再转化率。RNAi种子中的代谢重排导致了与硫相关的代谢的改变，如半胱氨酸和谷胱甘肽的含量减少，硫代葡萄糖苷的组成也不同。综上所述，这些数据提出了种子和莲座叶之间存在的一种新的串扰，以及在这些组织中运行的Asp家族和SMM途径之间的相互影响。他们还阐明了较高的蛋氨酸水平对种子生理和行为的影响。
S-Methylmethionine (SMM) was suggested previously to participate in the metabolism of methionine (Met) in seeds. To further reveal its roles, we had previously produced transgenic Arabidopsis (Arabidopsis thaliana) RNA interference (RNAi) seeds with lower transcript expression of CYSTATHIONINE gamma-SYNTHASE (AtCGS), Met's main regulatory enzyme. Unexpectedly, these seeds accumulated significantly higher levels of Met compared with control seeds through an as yet unknown mechanism. Here, transcript and metabolic analyses coupled with isotope-labeled [C-13] SMM and [C-13] Met feeding experiments enabled us to reveal that SMM that was synthesized in rosette leaves of RNAi plants significantly contributed to the accumulation of Met in their seeds at late stages of development. Seed-specific repression of AtCGS in RNAi seeds triggered the induction of genes operating in the SMM cycle of rosette leaves, leading to elevated transport of SMM toward the seeds, where higher reconversion rates of SMM to Met were detected. The metabolic rearrangements in RNAi seeds resulted in an altered sulfur-associated metabolism, such as lower amounts of Cys and glutathione, as well as a differential composition of glucosinolates. Together, the data propose a novel cross talk existing between seeds and rosette leaves along with mutual effects between the Asp family and SMM pathways operating in these tissues. They also shed light on the effects of higher Met levels on seed physiology and behavior.