Silva Liliana S, Seabra Ana R, Leitão José N, Carvalho Helena G
Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal; Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Portugal.
Instituto de Biologia Molecular e Celular da Universidade do Porto, Rua do Campo Alegre, 823, 4150-180 Porto, Portugal.
Plant Sci. 2015 Nov;240:98-108. doi: 10.1016/j.plantsci.2015.09.001. Epub 2015 Sep 3.
Genes containing domains related to glutamine synthetase of the prokaryotic type (GSI-like) are widespread in higher plants, but their function is currently unknown. To gain insights into the possible role of GSI-like proteins, we characterized the GSI-like gene family of Medicago truncatula and investigated the functionality of the encoded proteins. M. truncatula contains two-expressed GSI-like genes, MtGSIa and MtGSIb, encoding polypeptides of 454 and 453 amino acids, respectively. Heterologous complementation assays of a bacterial glnA mutant indicate that the proteins are not catalytically functional for glutamine synthesis. Gene expression was investigated by qRT-PCR and western blot analysis in different organs of the plant and under different nitrogen (N) regimes, revealing that both genes are preferentially expressed in roots and root nodules, and that their expression is influenced by the N-status of the plant. Analysis of transgenic plants expressing MtGSI-like-promoter-gusA fusion, indicate that the two genes are strongly expressed in the root pericycle, and interestingly, the expression is enhanced at the sites of nodule emergence being particularly strong in specific cells located in front of the protoxylem poles. Taken together, the results presented here support a role of GSI-like proteins in N sensing and/or signaling, probably operating at the interface between perception of the N-status and the developmental processes underlying both root nodule and lateral root formation. This study indicates that GSI-like genes may represent a novel class of molecular players of the N-mediated signaling events.
含有与原核生物型谷氨酰胺合成酶相关结构域（类GSI）的基因在高等植物中广泛存在，但其功能目前尚不清楚。为了深入了解类GSI蛋白的可能作用，我们对蒺藜苜蓿的类GSI基因家族进行了表征，并研究了编码蛋白的功能。蒺藜苜蓿含有两个表达的类GSI基因，MtGSIa和MtGSIb，分别编码454和453个氨基酸的多肽。对细菌glnA突变体的异源互补分析表明，这些蛋白对谷氨酰胺合成没有催化功能。通过qRT-PCR和蛋白质免疫印迹分析研究了该植物不同器官以及不同氮素（N）处理条件下的基因表达，结果表明这两个基因在根和根瘤中优先表达，并且它们的表达受植物氮素状态的影响。对表达MtGSI类启动子 - gusA融合基因的转基因植物的分析表明，这两个基因在根中柱鞘中强烈表达，有趣的是，在根瘤出现的部位表达增强，在原生木质部极前方的特定细胞中尤为强烈。综上所述，本文给出的结果支持类GSI蛋白在氮感知和/或信号传导中发挥作用，可能在氮素状态感知与根瘤和侧根形成的发育过程之间的界面起作用。这项研究表明，类GSI基因可能代表了一类新的氮介导信号事件的分子参与者。
