The HECT ubiquitin-protein ligase (UPL) family in Arabidopsis:: UPL3 has a specific role in trichome development
The HECT ubiquitin-protein ligase (UPL) family in Arabidopsis:: UPL3 has a specific role in trichome development
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DOI：
10.1046/j.1365-313x.2003.01844.x
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发表时间：
2003-09-01
期刊：
影响因子：
7.2
通讯作者：
Vierstra, RD
中科院分区：
文献类型：
--
作者：
Downes, BP;Stupar, RM;Vierstra, RD
一种或多种泛素(UBS)与多种细胞内蛋白的结合在植物中具有多种作用，包括26S蛋白酶体选择性地去除调节蛋白。这一修饰的最后一步是由泛素蛋白连接酶(E3)执行的，它促进Ub转移到适当的靶点。一个重要的E3家族是由Hect结构域的存在定义的，Hect结构域是首先在人类E3(E6-AP)的C末端发现的一个活性位点。以一个共有的Hect结构域为查询，我们在拟南芥中鉴定了一个由7个含有Hect的泛素蛋白连接酶(UPL1-UPL7)组成的家族，可分为四个亚家族。UPL3和UPL4亚家族编码约200 kDa的蛋白质，有4个Armadillo重复序列，与核孔蛋白Importin-a相似，表明这些E3通过与核定位序列结合来识别其靶标。虽然UPL3基因的T-DNA中断并不影响拟南芥的整体生长和发育，但突变体表现出异常的毛状体形态。许多Upl3毛状体包含五个或更多的分支，而不是形成三个分支。向上的毛状体还经常经历额外的一轮内复制，导致细胞核扩大，倍性水平高达64C。Upl3植物对赤霉酸-3(GA(3))高度敏感，这与赤霉素在毛状体发育中的作用一致。Upl3突变体的表型与Kaktus相似，Kaktus是一组先前描述的具有额外分枝的毛状体突变体。遗传分析证实，UPL3突变体和Kaktus-2与在UPL3转录区域内存在剪接点突变的Kaktus-2等位基因。总之，这些数据表明，UPL3泛素化一个或多个激活蛋白对于抑制拟南芥毛状体的过度分枝和内复制是必要的。
Attachment of one or more ubiquitins (Ubs) to various intracellular proteins has a number of roles in plants including the selective removal of regulatory proteins by the 26S proteasome. The final step in this modification is performed by ubiquitin-protein ligases (E3s) that promote Ub transfer to appropriate targets. One important family of E3s is defined by the presence of a HECT domain, an active site first found at the C-terminus of the human E3 (E6-AP). Using a consensus HECT domain as the query, we identified a family of seven HECT-containing ubiquitin-protein ligases (UPL1-UPL7) in Arabidopsis thaliana that can be grouped into four subfamilies. The UPL3 and UPL4 subfamily encodes approximately 200-kDa proteins with four Armadillo repeats similar to those in the nuclear pore protein importin-a, suggesting that these E3s identify their targets through binding to nuclear localization sequences. Although T-DNA disruptions of the UPL3 locus do not affect overall growth and development of Arabidopsis, the mutants show aberrant trichome morphology. Instead of developing three branches, many upl3 trichomes contain five or more branches. The upl3 trichomes also often undergo an additional round of endoreplication resulting in enlarged nuclei with ploidy levels of up to 64C. upl3 plants are hypersensitive to gibberellic acid-3 (GA(3)), consistent with the role of gibberellins in trichome development. The phenotype of upl3 mutants is similar to that of kaktus, a previously described set of trichome mutants with supernumerary branches. Genetic analyses confirmed that upl3 mutants and kaktus-2 are allelic with kaktus-2 plants harboring a splice-site mutation within the UPL3-transcribed region. Collectively, the data indicate that the ubiquitination of one or more activator proteins by UPL3 is necessary to repress excess branching and endoreplication of Arabidopsis trichomes.