The Arabidopsis RING-type E3 ligase XBAT32 mediates the proteasomal degradation of the ethylene biosynthetic enzyme, 1-aminocyclopropane-1-carboxylate synthase 7
The Arabidopsis RING-type E3 ligase XBAT32 mediates the proteasomal degradation of the ethylene biosynthetic enzyme, 1-aminocyclopropane-1-carboxylate synthase 7
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DOI：
10.1111/j.1365-313x.2012.04965.x
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发表时间：
2012-07-01
期刊：
影响因子：
7.2
通讯作者：
Stone, Sophia L.
中科院分区：
文献类型：
--
作者：
Lyzenga, Wendy J.;Booth, Judith K.;Stone, Sophia L.
E3泛素连接酶选择特定的蛋白质用于泛素缀合，并且修饰的蛋白质通常通过26 S蛋白酶体降解。XBAT 32是一种RING型E3连接酶，参与维持适当的乙烯水平。先前的研究表明，XBAT 32通过泛素化两种乙烯生物合成酶ACS 4（II型同种型）和ACS 7（III型同种型）来调节乙烯的产生。在拟南芥中，I型和II型1-氨基环丙烷-1-羧酸（ACC）合酶（ACS）同种型C-末端尾部内的保守序列影响泛素依赖的蛋白水解。ACS 7是唯一的拟南芥III型ACS，含有一个截短的C-末端尾，缺乏所有已知的调控序列，这表明这种亚型可能不会受到泛素介导的蛋白酶体降解。在这里，我们证明了在植物中，ACS 7是在一个26 S蛋白酶体依赖性的方式和ACS 7的降解需要E3连接酶XBAT 32翻转。此外，在野生型植物中由ACS 7的过表达引起的乙烯相关表型在xbat 32 -1中被大大夸大，表明需要XBAT 32来减弱ACS 7的过表达的作用。这一观察结果与XBAT 32在泛素介导的ACS 7降解中的作用一致。过表达ACS 7的xbat 32 -1幼苗的黑暗生长表型可以被ACS活性的抑制剂aminoethoxylvinylglycine有效地拯救。在不存在XBAT 32的情况下，ACS 4的降解速率也显著较慢，进一步暗示XBAT 32参与了ACS 4的泛素介导的降解。总之，这些结果表明，XBAT 32靶向乙烯生物合成酶进行蛋白酶体降解，以维持适当水平的激素产生。
E3 ubiquitin ligases select specific proteins for ubiquitin conjugation, and the modified proteins are commonly degraded through the 26S proteasome. XBAT32 is a RING-type E3 ligase involved in maintaining appropriate levels of ethylene. Previous work has suggested that XBAT32 modulates ethylene production by ubiquitinating two ethylene biosynthesis enzymes, ACS4 (type-II isoform) and ACS7 (type-III isoform). In Arabidopsis, conserved sequences within the C-terminal tail of type-I and -II 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) isoforms influence ubiquitin-dependent proteolysis. ACS7, the sole Arabidopsis type-III ACS, contains a truncated C-terminal tail that lacks all known regulatory sequences, which suggests that this isoform may not be subject to ubiquitin-mediated proteasomal degradation. Here we demonstrate in planta that ACS7 is turned over in a 26S proteasome-dependent manner and that degradation of ACS7 requires the E3 ligase XBAT32. Furthermore, the ethylene-related phenotypes that result from overexpression of ACS7 in wild-type plants are greatly exaggerated in xbat32-1, suggesting that XBAT32 is required to attenuate the effect of overexpression of ACS7. This observation is consistent with a role for XBAT32 in the ubiquitin-mediated degradation of ACS7. The dark-grown phenotype of xbat32-1 seedlings overexpressing ACS7 can be effectively rescued by aminoethoxyvinylglycine, an inhibitor of ACS activity. The degradation rate of ACS4 is also significantly slower in the absence of XBAT32, further implicating XBAT32 in the ubiquitin-mediated degradation of ACS4. Altogether, these results demonstrate that XBAT32 targets ethylene biosynthetic enzymes for proteasomal degradation to maintain appropriate levels of hormone production.