玉米中ClassⅠ和ClassⅡNAS蛋白之间的BiFC互作研究

Interactions Between ClassⅠand ClassⅡNAS Proteins in Maize Using Bimolecular Fluorescence Complementation(BiFC)Assay

烟草胺合成酶(nicotianamine synthase,NAS)能够催化合成植物体内铁运输所需的螯合物烟草胺(nicotianamine,NA),在植物维持铁稳态方面发挥重要的作用。玉米、小麦和大麦等禾本科植物的NAS蛋白进化为ClassⅠ和ClassⅡ两个亚家族,可能分别参与调节铁的吸收和运输,其家族成员之间蛋白序列同源性较高,ClassⅡNAS具有特异的N端可变结构域。通过进化分析分析玉米NAS的两个亚家族,以及建模预测两类亚家族代表基因ZmNAS1(ClassⅠ)和ZmNAS3(ClassⅡ)的蛋白结构,结果表明ZmNAS1和ZmNAS3的三维结构高度相似,推测可能通过同源或异源二聚体化发挥功能;进一步通过双分子荧光互补(bimolecular fluorescence complementation,BiFC)分析ZmNAS1和ZmNAS3的相互作用,结果表明,ZmNAS1和ZmNAS3蛋白可以互作,删除N端可变结构域的ZmNAS3ΔN只能与ZmNAS3蛋白互作而不与ZmNAS1互作,推测ZmNAS可以形成同源二聚体,而形成异源二聚体需要ClassⅡ家族蛋白的N端可变结构域。研究结果揭示了玉米中ClassⅡNAS调控铁稳态的机制,其分子机制仍需进一步研究。

Nicotianamine synthase(NAS)catalyzes the synthesis of nicotianamine(NA),a chelate required for iron transport in plants,which plays an important role in remaining iron homeostasis in plants.The NAS proteins of graminaceous plants,such as maize,wheat and barley,evolved into two subfamilies,ClassⅠand ClassⅡ,which may participate in iron absorption and trans⁃port respectively.There is high homology between family members,ClassⅡNAS have specific N-terminal variable domains.This study analyzed evolution of two subfamilies of NAS,and predicted three-dimensional structures of the representative proteins(ZmNAS1 and ZmNAS3)in ClassⅠand ClassⅡthrough modeling.The result suggested that,three-dimensional structures of ZmNAS1 and ZmNAS3 were highly similar,speculating that the function of NAS proteins might through homologous or heterolo⁃gous dimerization.Furthermore,the interaction between ZmNAS1 and ZmNAS3 was also studied using bimolecular fluorescence complementation(BiFC)through transient expression in mesophyll protoplasts.BiFC results showed that ZmNAS1 interacted with ZmNAS3,while ZmNAS3ΔN(lack of the N-terminal variable domain)only interacted with ZmNAS3 but not with ZmNAS1.In summary,ZmNAS can form homologous dimers,while the formation of heterologous dimers requires the N-terminal variable domain of ClassⅡfamily proteins.Therefore,the results revealed the mechanism of ClassⅡNAS regulating homeostasis in maize and the molecular mechanism remains to be further studied.