Diverse nitrogen signals activate convergent ROP2-TOR signaling in Arabidopsis

背景回顾The evolutionarily conserved target-of-rapamycin (TOR) kinase coordinates cellular and organismal growth in all eukaryotes. 

提出问题：Amino acids (AAs) are key upstream signals for mammalian TOR activation, but how nitrogen-related nutrients regulate TOR signaling in plants is poorly understood.

主要发现：Here, we discovered that, independent of nitrogen assimilation, nitrate and ammonium function as primary nitrogen signals to activate TOR in the Arabidopsis leaf primordium. 

结果1-激活TOR的氨基酸：We further identified that a total of 15 proteinogenic AAs are also able to activate TOR, and the first AAs generated from plant specific nitrogen assimilation (glutamine), sulfur assimilation (cysteine), and glycolate cycle (glycine), exhibit the highest potency. 

结果2-氮-ROP2-TOR：Interestingly, nitrate, ammonium, and glutamine all activate the small GTPase Rho-related protein from plants 2 (ROP2), and constitutively active ROP2 restores TOR activation under nitrogen-starvation conditions. 

结论：Our findings suggest that specific evolutionary adaptations of the nitrogen-TOR signaling pathway occurred in plant lineages, and ROP2 can integrate diverse nitrogen and hormone signals for plant TOR activation.

 摘 要 

雷帕霉素靶蛋白（TOR）激酶在演化上比较保守，在所有的真核生物中起协调细胞和器官生长的作用。氨基酸是哺乳动物TOP激活关键的上游信号，但是氮相关的营养如何调控植物中TOR信号转导还不清楚。本文中，作者发现在拟南芥的叶原基中，硝酸盐和铵盐作为主要的氮信号，不依赖于氮同化作用于TOR的激活。作者进一步鉴定了15个同样能够激活TOR的蛋白氨基酸，并且植物特异的氮同化、硫同化和乙醇酸循环所产生的第一种氨基酸（分别是谷氨酰胺、半胱氨酸和甘氨酸）激活TOR的潜力最高。有趣的是，硝酸盐、铵盐和谷氨酰胺都能激活植物ROP2蛋白，并且具备组成型活性的ROP2在氮饥饿条件下能够恢复TOR的激活。本文的研究说明植物这一支系发生了特异的氮-TOR信号转导通路的演化适应性，并且ROP2可以整合不同的氮和激素信号以激活植物TOR。