Genomic Survey, Gene Expression, and Interaction Analysis Suggest Diverse Roles of ARF and Aux/IAA Proteins in Solanaceae

Auxin response factor (ARF) and Auxin/INDOLE-3-ACETIC ACID (Aux/IAA) proteins are the foremost regulators of auxin action and play an essential role in the coordination of many aspects of plant growth and development. Though many members of both ARF and Aux/IAA gene families have been identified and characterized in tomato, they are less studied in other Solanaceae species. In the present study, we focused on gaining insights into their functional conservation as well as diversification during auxin-mediated responses in Solanaceae. First, we identified their full complement in tomato, potato, pepper, Nicotiana benthamiana, eggplant, and petunia and found that both the gene families have expanded in N. benthamiana. We also looked into the structural variations associated with all the members of these two classes of genes in tomato and showed that huge natural variation exists in their sequence in wild relatives. The comprehensive gene expression analysis provided evidence of high conservation in the expression of orthologous ARFs and Aux/IAAs during fruit development and ripening in tomato and pepper. Furthermore, the molecular changes caused by exogenous plant hormones and abiotic stress conditions on their transcript levels were investigated which showed that many members of both the gene families may participate in various hormone- and stress-mediated responses in tomato and potato. Some of these genes may play a role in linking the hormone-controlled plant growth and stress-related signaling pathways. Finally, we demonstrate that single tomato ARF can interact with multiple Aux/IAA proteins and vice versa. Overall, our study will be very helpful in establishing both conserved as well as non-conserved functions of these genes in Solanaceae.