Two Arabidopsis threonine aldolases are nonredundant and compete with threonine deaminase for a common substrate pool
Two Arabidopsis threonine aldolases are nonredundant and compete with threonine deaminase for a common substrate pool
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DOI：
10.1105/tpc.106.044958
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发表时间：
2006-12-01
期刊：
影响因子：
11.6
通讯作者：
Jander, Georg
中科院分区：
文献类型：
--
作者：
Joshi, Vijay;Laubengayer, Karen M.;Jander, Georg
氨基酸不仅是蛋白质的基本成分，而且是许多植物必需代谢产物的前体。虽然氨基酸在植物中的生物合成途径已经确定，但途径调控、分解代谢和下游代谢物分配仍然相对未被研究。苏醛缩酶（EC 4.1.2.5）将苏醛转化为甘氨酸和乙醛只是最近才被证明在植物氨基酸代谢中起作用。拟南芥苏醛缩酶（Thr aldolase, THA1）主要在种子和幼苗中表达，而另一种（THA2）则在整个植物的维管组织中表达。该突变体的代谢物分析发现，种子苏氨酸含量增加了50倍，幼苗甘氨酸含量减少了50%，其他代谢变化很少。相比之下，纯合的tha2突变导致致命的白化表型。通过过度产生反馈不敏感的苏脱氨酶（OMR1）来拯救tha2突变体和tha1 tha2双突变体，表明在拟南芥中，tha1和tha2的Gly形成不是必需的。th1和th2 Thr醛缩酶突变体对反馈不敏感的Thr脱氨酶的种子特异性表达大大增加了种子IIe含量，表明这两种Thr分解代谢酶竞争一个共同的底物库。
Amino acids are not only fundamental protein constituents but also serve as precursors for many essential plant metabolites. Although amino acid biosynthetic pathways in plants have been identified, pathway regulation, catabolism, and downstream metabolite partitioning remain relatively uninvestigated. Conversion of Thr to Gly and acetaldehyde by Thr aldolase (EC 4.1.2.5) was only recently shown to play a role in plant amino acid metabolism. Whereas one Arabidopsis thaliana Thr aldolase (THA1) is expressed primarily in seeds and seedlings, the other (THA2) is expressed in vascular tissue throughout the plant. Metabolite profiling of tha1 mutants identified a > 50-fold increase in the seed Thr content, a 50% decrease in seedling Gly content, and few other significant metabolic changes. By contrast, homozygous tha2 mutations cause a lethal albino phenotype. Rescue of tha2 mutants and tha1 tha2 double mutants by overproduction of feedback-insensitive Thr deaminase (OMR1) shows that Gly formation by THA1 and THA2 is not essential in Arabidopsis. Seed-specific expression of feedback-insensitive Thr deaminase in both tha1 and tha2 Thr aldolase mutants greatly increases seed IIe content, suggesting that these two Thr catabolic enzymes compete for a common substrate pool.