PHO2-Dependent Degradation of PHO1 Modulates Phosphate Homeostasis in Arabidopsis
PHO2-Dependent Degradation of PHO1 Modulates Phosphate Homeostasis in Arabidopsis
复制标题
DOI：
10.1105/tpc.112.096636
复制
发表时间：
2012-05-01
期刊：
影响因子：
11.6
通讯作者：
Chiou, Tzyy-Jen
中科院分区：
文献类型：
--
作者：
Liu, Tzu-Yin;Huang, Teng-Kuei;Chiou, Tzyy-Jen
拟南芥pho2突变体是一种泛素偶联E2酶缺陷的突变体，由于无机磷酸盐（Pi）的吸收增强和根到茎的转运，表现出无机磷酸盐（Pi）毒性。为了阐明pho2依赖性调控途径的下游组分，我们确定了两个pho2抑制子，它们在PHO1中携带错义突变，这与Pi装载到木质部有关。为了支持PHO1和PHO2之间的遗传相互作用，我们发现PHO1蛋白水平在PHO2中增加，而这种积累在PHO2抑制基因中都得到了改善。环己亚胺和内体Cys蛋白酶抑制剂E-64d处理的结果进一步表明，PHO1的降解依赖于PHO2，并涉及多泡体介导的空泡蛋白水解。利用烟草叶片的瞬时表达系统，我们发现PHO1和PHO2在烟草内膜中部分共定位并相互作用，PHO2的泛素偶联酶活性是PHO1降解所必需的。此外，PHO1突变导致的PHO1表达减少阻碍了Pi的摄取，这表明木质部装载与Pi的获取之间存在功能关联。总之，我们的发现揭示了PHO2调节PHO1在植物膜中的降解以维持Pi稳态的关键分子机制。
The Arabidopsis thaliana pho2 mutant, which is defective in a ubiquitin-conjugating E2 enzyme, displays inorganic phosphate (Pi) toxicity as a result of enhanced uptake and root-to-shoot translocation of Pi. To elucidate downstream components of the PHO2-dependent regulatory pathway, we identified two pho2 suppressors as carrying missense mutations in PHO1, which has been implicated in Pi loading to the xylem. In support of the genetic interaction between PHO1 and PHO2, we found that the protein level of PHO1 is increased in pho2, whereas such accumulation is ameliorated in both pho2 suppressors. Results from cycloheximide and endosomal Cys protease inhibitor E-64d treatments further suggest that PHO1 degradation is PHO2 dependent and involves multivesicular body-mediated vacuolar proteolysis. Using the transient expression system of tobacco (Nicotiana tabacum) leaves, we demonstrated that PHO1 and PHO2 are partially colocalized and physically interact in the endomembranes, where the ubiquitin conjugase activity of PHO2 is required for PHO1 degradation. In addition, reduced PHO1 expression caused by PHO1 mutations impede Pi uptake, indicating a functional association between xylem loading and acquisition of Pi. Together, our findings uncover a pivotal molecular mechanism by which PHO2 modulates the degradation of PHO1 in the endomembranes to maintain Pi homeostasis in plants.