A network approach to investigating the role of the Sorghum bicolor transcription factor SbWRKY86 in promoting plant resistance to aphids
Plants defend themselves against pathogens and pests by mounting complex responses involving many defensive genes, proteins and metabolites. These immune responses are often activated by transcription factors that regulate expression of genes required for immunity. Melanaphis sacchari (Sugar cane aphid, SCA) has become a major pest to Sorghum bicolor (sorghum), posing a threat to this livestock feeding and biofuel producing plant. Recently, a sorghum transcription factor, SbWRKY86, was identified through a genome-wide association study as being associated with SCA resistance and was subsequently shown to confer aphid resistance when ectopically expressed in both Nicotiana benthamiana and Arabidopsis thaliana. However, how SbWRKY86 promotes aphid resistance was not understood. Here, we investigated the resistance phenotype further through transcriptomic profiling of transgenic Arabidopsis thaliana lines heterologously expressing SbWRKY86 as a fusion with yellow fluorescent protein and under the control of the Cauliflower Mosaic Virus (CaMV) 35S constitutive promoter (35S::SbWRKY86-YFP lines). Genes that were differentially expressed in 35S::SbWRKY86-YFP lines were extracted and used to probe a predicted protein-protein interaction (PPI) network. The integrated analysis identified potential network components associated with SbWRKY86 function. Specifically, a network of genes related to carbon/nitrogen metabolism, production of the cell wall polymer callose, and heat shock proteins were upregulated in these lines. Visualization of callose deposits in the leaves of 35S::SbWRKY86-YFP plants demonstrated increased frequency as compared to wild type in response to the immunostimulatory microbe-associated molecular pattern flg22. These results suggest that SbWRKY86 may in part mediate resistance to M. sacchari through regulation of callose production.