重金属相关异戊二烯化植物蛋白HIPP是一类含有金属结合结构域(HMA)和C端异戊二烯化基序的金属伴侣蛋白.该文总结了模式植物中HIPP蛋白的结构特征,阐述了植物HIPP蛋白家族参与的重金属稳态和解毒机制,揭示了其在植物生长发育和应对环境变化(生物和非生物胁迫)中的潜在意义,以期为HIPP蛋白家族的后续研究提供启示.

金属伴侣在植物的生理活动中发挥关键作用,负责结合金属离子并将其转运至靶蛋白以维持细胞的金属离子稳态.目前关于HIPP(heavy metal-associated isoprenylated plant protein)金属伴侣蛋白的特性和功能分析多集中于模式植物拟南芥.本研究在毛果杨(Populus trichocarpa)中鉴定了14个PtHIPPs蛋白,均具有两个保守的金属离子结合基序MXCXXC,氨基末端可以形成βαββαβ二级结构,羧基末端具有保守的异戊二烯化基序;一些PtHIPPs还具有赖氨酸和/或甘氨酸富集区.根据基因结构、蛋白质的保守基序和进化树分析,PtHIPPs蛋白可分为3个亚组.PlantGenIE的组织特异性表达数据及荧光定量PCR鉴定结果显示,毛果杨PtHIPPs基因及小黑杨(Populus simonii× Populus nigra)PnHIPPs基因具有特定的组织表达特异性且存在差异.此外,利用缺铜及过量铜离子处理小黑杨植株不同时间后,不同组织部位中PnHIPPs基因的表达模式发生改变.本研究为鉴定木本模式植物杨树HIPPs蛋白在维持铜离子稳态过程中发挥的作用提供了参考依据.

Eukaryotic organisms are equipped with quality-control mechanisms that survey protein folding in the endoplasmic reticulum (ER) and remove non-native proteins by ER-associated degradation (ERAD).Recent research has shown that cytokinin-degrading CKX proteins are subjected to ERAD during plant develop-ment,The mechanisms of plant ERAD,including the export of substrate proteins from the ER,are not fully understood,and the molecular components involved in the ERAD of CKX are unknown.Here,we show that heavy metal-associated isoprenylated plant proteins (HIPPs) interact specifically with CKX proteins syn-thesized in the ER and processed by ERAD.CKX-HIPP protein complexes were detected at the ER as well as in the cytosol,suggesting that the complexes involve retrotranslocated CKX protein species.Altered CKX levels in HIPP-overexpressing and higher-order hipp mutant plants suggest that the studied HIPPs control the ERAD of CKX.Deregulation of CKX proteins caused corresponding changes in the cyto-kinin signaling activity and triggered typical morphological cytokinin responses,Notably,transcriptional repression of HIPP genes by cytokinin indicates a feedback regulatory mechanism of cytokinin homeosta-sis and signaling responses.Moreover,loss of function of HIPP genes constitutively activates the unfolded protein response and compromises the ER stress tolerance.Collectively,these results suggests that HIPPs represent novel functional components of plant ERAD.

重金属相关异戊二烯化植物蛋白(HIPPs,heavy metal-associated isoprenylated plant proteins)是金属离子在植物细胞内安全运输的关键蛋白,在植物体金属离子稳态的维持过程中发挥重要作用.目前关于HIPPs基因家族的研究多集中于模式植物水稻(Oryza sativa L.)和拟南芥(Arabidopsis thaliana(L.)Heynh.),在甘蓝型油菜(Brassica napus L.)中报道相对较少.本研究通过生物信息学的方法在甘蓝型油菜全基因组(Darmor-bzh v10)中鉴定到了不均匀分布在19条染色体上的104个BnaHIPPs基因.蛋白理化性质分析发现其氨基酸数目在120～630 aa,蛋白分子量在13827.56～64467.05 ku,平均等电点为8.07,蛋白平均疏水指数在-1.146～-0.17之间.基因表达模式分析发现它们在不同组织和发育时期的表达模式具有一定的时空表达特性,在根中的表达量最高.镉胁迫处理条件下BnaHIPPs的表达模式发生了改变,BnaA08p24150、BnaA09p41730和BnaC06p45180在根和叶片中的相对表达水平都发生了上调.系统进化关系显示BnaHIPPs基因被分为5个亚家族.此外,共线性分析显示在BnaHIPPs基因的进化过程中,大多数的BnaHIPPs都是以片段复制的形式参与BnaHIPPs基因家族的扩张过程,仅发现BnaC05p3800、BnaC05p3810、BnaC05p3820和BnaC05p3830以串联重复的形式参与BnaHIPPs的复制事件.本研究结果将为甘蓝型油菜BnaHIPPs基因家族的进一步研究奠定基础.