Genome-Wide Characterization of Glutamine Synthetase Family Genes in Cucurbitaceae and Their Potential Roles in Cold Response and Rootstock-Scion Signaling Communication

Abstract

Glutamine synthetase (GS; EC 6.3.1.2, L-glutamate: ammonia ligase ADP-forming) is the key enzyme responsible for the primary assimilation and reassimilation of nitrogen (N) in higher plants. There are two main isoforms of GS in higher plants, classified as cytosolic GS (GS1) and chloroplastic GS (GS2) by their size and subcellular localization. In order to improve the stress tolerance, quality, and yield of cucurbit crops such as cucumbers (Csa, Cucumis sativus L.), pumpkins (Cmo, Cucurbita moschata var. Rifu) are often used as rootstocks. Here, the GS family of the two species were comprehensively analyzed using bioinformatics in terms of aspects of the phylogenic tree, gene structure, chromosome location, subcellular localization, and evolutionary and expression patterns. Seven and four GS gene family members were screened in pumpkin and cucumber, respectively. GS family genes were divided into three groups (one for GS2 and two for GS1) according to their homology and phylogenetic relationships with other species. The analysis of gene ontology annotation of GS family genes, promoter regulatory elements, and tissue-specific expression patterns indicates the potential different biological roles of GS isoforms in Cucurbitaceae. In particular, we have identified a potentially available gene (GS1: CmoCh08G004920) from pumpkin that is relatively highly expressed and tissue-specifically expressed. RT-PCR analysis showed that most CmoGSs are induced by low temperature, and long-term (day 2 to day 9) cold stress has a more obvious effect on the RNA abundance of CmoGS. Our work presents the structure and expression patterns of all candidate members of the pumpkin and cucumber GS gene family, and to the best of our knowledge, this is the first time such work has been presented. It is worth focusing on the candidate genes with strong capacity for improving pumpkin rootstock breeding in order to increase nitrogen-use efficiency in cold conditions, as well as rootstock-scion communication.