Two RING-Finger Ubiquitin E3 Ligases Regulate the Degradation of SPX4, An Internal Phosphate Sensor, for Phosphate Homeostasis and Signaling in Rice
Two RING-Finger Ubiquitin E3 Ligases Regulate the Degradation of SPX4, An Internal Phosphate Sensor, for Phosphate Homeostasis and Signaling in Rice
复制标题
两个环指泛素 E3 连接酶调节 SPX4（一种内部磷酸盐传感器）的降解，用于水稻中的磷酸盐稳态和信号传导
DOI：
10.1016/j.molp.2019.04.003
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发表时间：
2019
期刊：
影响因子：
27.5
通讯作者：
Yi Keke
中科院分区：
文献类型：
--
作者：
Ruan Wenyuan;Guo Meina;Wang Xueqing;Guo Zhenhui;Xu Zhuang;Xu Lei;Zhao Hongyu;Sun Haiji;Yan Chengqi;Yi Keke
含SPX结构域的蛋白(SPX)在真核生物的无机磷(PI)传感、信号转导和转运中发挥着重要作用。在植物中，SPX可以整合细胞内的PI状态，并负向调节PI中央调节器的活性，即磷酸饥饿反应蛋白(PHR)。在PI不足的条件下，SPX，如SPX4的稳定性降低。然而，SPX被降解的机制仍不清楚。在本研究中，通过酵母双杂交筛选，我们鉴定了两个调控SPX4降解的环指泛素E3连接酶，命名为SDEL1和SDEL2，它们是由Pi饥饿后转录诱导的。我们发现，这两个SDELs都位于胞核和胞浆中，具有泛素E3连接酶活性，并直接泛素化SPX4中的K213和K299赖氨酸残基来调节其稳定性。此外，我们还发现水稻中的PI中央调节因子PHR2可以在PI充足的条件下与SPX4相互作用，从而保护SPX4不被泛素化和降解。与SDEL1和SDEL2的生化功能一致，即使在PI充足的条件下，SDEL1或SDEL2的过表达也会导致PI的过度积累并诱导PI饥饿信号。相反，它们的功能缺失突变体表现出PI积累减少和PI饥饿信号减少。总之，我们的研究表明，SDEL1和SDEL2促进了SPX4的降解，以调节PHR2的活性，并调节水稻体内的PI动态平衡和PI信号，以响应外部PI的可利用性。
SPX-domain-containing proteins (SPXs) play an important role in inorganic phosphate (Pi) sensing, signaling, and transport in eukaryotes. In plants, SPXs are known to integrate cellular Pi status and negatively regulate the activity of Pi central regulators, the PHOSPATE STARVATION RESPONSE proteins (PHRs). The stability of SPXs, such as SPX4, is reduced under Pi-deficient conditions. However, the mechanisms by which SPXs are degraded remain unclear. In this study, using a yeast-two-hybrid screen we identified two RING-finger ubiquitin E3 ligases regulating SPX4 degradation, designated SDEL1 and SDEL2, which were post-transcriptionally induced by Pi starvation. We found that both SDELs were located in the nucleus and cytoplasm, had ubiquitin E3 ligase activity, and directly ubiquitinated the K213and K299lysine residues in SPX4 to regulate its stability. Furthermore, we found that PHR2, a Pi central regulator in rice, could compete with SDELs by interacting with SPX4 under Pi-sufficient conditions, which protected SPX4 from ubiquitination and degradation. Consistent with the biochemical function of SDEL1 and SDEL2, overexpression ofSDEL1orSDEL2resulted in Pi overaccumulation and induced Pi-starvation signaling even under Pi-sufficient conditions. Conversely, their loss-of-function mutants displayed decreased Pi accumulation and reduced Pi-starvation signaling. Collectively, our study revealed that SDEL1 and SDEL2 facilitate the degradation of SPX4 to modulate PHR2 activity and regulate Pi homeostasis and Pi signaling in response to external Pi availability in rice.