Functional Analysis of Mitogen Activated Protein Kinase Superfamily in Solanaceae

Abstract

Mitogen-activated protein kinase (MAPK) is an essential gene superfamily with central roles in plant signaling. In plants, their functions include growth, development and stress response. It is divided into three families which control various cellular processes. The current study was focused on identification of MAP Kinases (MPKs), MAPK Kinases (MKKs) and MAPK Kinase Kinases (MAPKKK) from economically important crops of Solanaceae (tomato, potato, eggplant, pepper and tobacco) along with a syntenic species from Rubiaceae (wild coffee), based on their conserved domains and signature motifs. Multiple sequence alignments were performed and heat plots were generated. Phylogenetic trees were constructed via neighbor joining and maximum likelihood methods. Homology modeling was performed and the resulting three- dimensional structures were refined and optimized. Structural superimpositions were performed. Protein-lipid interactions were tested by dockings. Protein-protein interactions were tested using bimolecular fluorescence complementation and the results were visualized via confocal microscopy. Based on high sequence similarities, the total number of genes identified as MAPKs were 89 in tomato, 108 in potato, 63 in eggplant, 79 in pepper, 64 in coffee and 162 in tetraploid tobacco. All genes in tomato, potato, pepper and coffee spread uniformly on their chromosomes. Grouping of various genes in the phylogenetic trees was in accordance with the homologous Arabidopsis MAPKs. High sequence similarities led to high structural similarity in Constitutive Triple Response 1 protein in tomato, potato, eggplant, pepper and coffee. Phosphoglycerides, natural lipids in plants, were found to form hydrogen bonds and hydrophobic interactions with this protein. MPKs and MKKs in tomato and pepper were seen to show interactions via strong fluorescence signals in the nucleus and endoplasmic reticulum. MPK3 interacted with MKK2 and MKK5, and similar interactions were observed for MPK4 in both pepper and tomato. Hence, it was confirmed that multiple MPKs interact with a single MKK, and vice versa. The MAPKs thus form a complex interactome in the cell. This study would be helpful in future studies on MAPK functions in order to understand the cellular mechanisms at protein levels under various environmental conditions and this knowledge would be utilized for generating better crop varieties to achieve higher yield.