Identification of rice melatonin receptor OsPMTR and its comparative in silico analysis with arabidopsis AtCAND2 receptor

Melatonin (N-acetyl-5-methoxytryptamine) is a signaling molecule having crucial role in plant growth, development and stress responses. Melatonin receptor has been identified in Arabidopsis, maize, tobacco and cassava. However no bona fide receptor has been identified in rice. Here we have identified a homolog of Arabidopsis melatonin receptor (AtCAND2/PMTR1) in rice OsPMTR. It is predicted to be a plasma membrane localized, seven transmembrane domain containing protein resembling G-protein coupled receptor. The comparative in silico analysis revealed that OsPMTR has similar gene structure and physiochemical properties as that of AtCAND2/PMTR1. Molecular docking analysis of OsPMTR and melatonin revealed pKi and ligand efficiency that were comparable to that of AtCAD2 which indicates strong possible interaction between OsPMTR and melatonin. To further elucidate melatonin signaling, we identified 24 potential interacting partners of OsPMTR using in silico protein-protein interaction, and also identified co-expression network of OsPMTR. OsRGA1, a known downstream signaling protein in G-protein mediated pathway, was identified as one of the interacting partners. We confirmed the interaction of OsPMTR with OsRGA1 through molecular docking. The quantitative expression analysis revealed that OsPMTR, two interacting partners (OsRGA1, OsCOLD1) and four co-expressed genes (OsTGA2.1, OsWRKY90, OsDREB6/OsERF60 and OsTCP5) were significantly induced by exogenous melatonin treatment in rice. This further suggests a potential role of OsPMTR interacting partners and coexpressed genes in OsPMTR signaling pathway. Our study shows that OsPMTR may act as a G-protein coupled receptor (GPCR) which activates the G-protein signaling through the downstream α subunit (OsRGA1) and may transcriptionally regulate many transcription factors and genes related to plant growth, development, biotic and abiotic stress tolerance. Our findings lay the foundation for the future experimental investigation in plant system to bring out the functional role of OsPMTR as a melatonin receptor and its signaling pathway in rice. This will further help develop cheap agonists and orthogonal receptors for management of abiotic stress tolerance and yield of crops. © 2017 Elsevier Inc. All rights reserved.