Asymmetric expression of a poplar ACC oxidase controls ethylene production during gravitational induction of tension wood
Asymmetric expression of a poplar ACC oxidase controls ethylene production during gravitational induction of tension wood
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DOI：
10.1046/j.1365-313x.2003.01727.x
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发表时间：
2003-05-01
期刊：
影响因子：
7.2
通讯作者：
Sundberg, B
中科院分区：
文献类型：
--
作者：
Andersson-Gunnerås, S;Hellgren, JM;Sundberg, B
乙烯是在木材形成组织中产生的，当外源应用时，它已被证明对木材发育的模式和速度产生深远的影响。然而，在木材形成过程中乙烯生物合成的分子调控尚不清楚。我们在杨树(Populus tremula （L.) x P. tremuloides (micx)）的成木组织中发现了一个丰富的1-氨基环丙烷-1-羧酸（ACC）氧化酶基因（PttACO1）。PttACO1主要在次生木质部发育过程中表达，在次生木质部壁形成过程中表达上调。然而，根据GC-MS分析结合切向冷冻切片，发现ACC在形成区组织中的分布相当均匀。重力刺激导致茎上侧张力材形成，导致张力材形成组织中PttACO1表达和ACC氧化酶活性的强烈诱导。ACC水平与PttACO1表达同步升高。然而，在茎的上侧（张力木）增加的很少，而在茎的下侧（相对）积累了大量的ACC及其可水解共轭物。这表明，相对较低水平的ACC在张力木材一侧是由其转化为乙烯的PttACO1高度上调的结果，而ACC在木材另一侧的同时积累是由于较低的PttACO1水平。我们得出结论，PttACO1和ACC氧化酶活性在重力刺激下杨树茎内不对称乙烯生产的控制中起重要作用，而不是ACC有效性。
Ethylene is produced in wood-forming tissues, and when applied exogenously, it has been shown to cause profound effects on the pattern and rate of wood development. However, the molecular regulation of ethylene biosynthesis during wood formation is poorly understood. We have characterised an abundant 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene (PttACO1 ) in the wood-forming tissues of Populus tremula (L.) x P. tremuloides (Michx). PttACO1 is primarily expressed in developing secondary xylem, and is specifically upregulated during secondary wall formation. Nevertheless, according to GC-MS analysis combined with tangential cryosectioning, the distribution of ACC was found to be fairly uniform across the cambial-region tissues. Gravitational stimulation, which causes tension wood to form on the upper side of the stem, resulted in a strong induction of PttACO1 expression and ACC oxidase activity in the tension wood-forming tissues. The ACC levels increased in parallel to the PttACO1 expression. However, the increase on the upper (tension wood) side was only minor, whereas large amounts of both ACC and its hydrolysable conjugates accumulated on the lower (opposite) side of the stem. This suggests that the relatively low level of ACC on the tension wood side is a result of its conversion to ethylene by the highly upregulated PttACO1, and the concurrent accumulation of ACC on the opposite side of the wood is because of the low PttACO1 levels. We conclude that PttACO1 and ACC oxidase activity, but not ACC availability, are important in the control of the asymmetric ethylene production within the poplar stem when tension wood is induced by gravitational stimulation.