N-α-乙酰转移酶B(NatB)调控植物乙烯合成的机制

Molecular mechanism of N-α-acetyltransferase B(NatB)in regulating ethylene biosynthesis in plant

N-α-乙酰转移酶(NAT)催化的N-末端乙酰化(NTA)是发生在真核生物细胞质中的一种普遍的蛋白质修饰,可影响多种生命活动过程。乙烯是重要的植物生长调节因子,其生物合成和调控对维持其在植物体内的正常水平和稳态至关重要,然而对乙烯稳态调控的研究多集中在转录水平,尚未有蛋白N-末端乙酰化参与其生物合成调控的报导。本论文对NatB复合体催化亚基和辅助亚基缺失拟南芥突变体nbc-1和ckrc3进行了研究。结果发现,NatB缺失表现出顶钩缺陷的表型和不正常的乙烯响应。对蛋白质组学结果分析发现ckrc3、nbc-1和ckrc3 nbc-1突变体中乙烯合成关键酶ACO_(2)/3/4蛋白含量明显降低。激素测定结果表明,NatB缺失导致乙烯的合成减少而ACC积累。NatB缺陷的表型能够被外源施加乙烯所恢复,而不能被乙烯的直接前体ACC恢复。综上,NatB介导的NTA通过影响乙烯合成关键酶的蛋白稳定性从而参与调控其合成,揭示了蛋白修饰对激素稳态维持和生长发育调控的重要作用。

N-terminal acetylation(NTA)is a form of a highly abundant protein modification in eukaryotes in which the acetyl group of acetyl-CoA as donor is transferred to theα-amino group of a protein at its N-terminus under the catalysis of N-α-acetyltransferases(NATs),the modified N-terminus that may affect many normal cellular lives.The ethylene plays key roles in regulating plant growth and development,which depends on an intricate homeostasis that is determined by the balance between its biosynthesis and metabolism.Despite of numerous reports on the transcriptional regulation of ACO genes,little is known about those at the post-translational protein level.In this study,ckrc3 and nbc-1 were systematically studied,and we found that NTA catalyzed by NatB can stabilize some members of ACO proteins and contribute to regulating the homeostasis of ethylene in plant.The major findings are listed as below:Proteomics profiling data showed that ACO2/3/4 abundances were reduced in ckrc3 nbc-1 compared with that in Col-7,the low ethylene level and accumulation of ACC caused by down-regulation of ACOs led to defects in apical hook and the nomal response of ethylene in the dark.These ethylene-related phenotypes could be fully rescued by application of exogenous ethylene,but less by its precursor ACC,confirming the involvement of NatB in regulating ethylene biosynthesis and homeostasis by affecting the stability of ACOs.In summary,Nat B-mediated NTA of ACOs play significant roles in ethylene biosynthesis for normal growth and development,revealing a previously little-known mechanism at the protein translation levels regulating hormone homeostasis and plants growth and development.