Exploring the boundaries of networks in the study of resistance against Ralstonia solanacearum

Solanum dulcamara displays partial resistance to the devastating bacterial pathogen Ralstonia solanacearum, with S. dulcamara plants showing delayed or no symptoms (Sebastià, et al, 2021). This trait, as well as studies identifying that their root exudates can transfer resistance to Solanum lycopersicum, a susceptible crop, makes S. dulcamara a key plant for understanding resistance to R. solanacearum (Franco Ortega, in press). The following study aims to develop from this finding by exploring the boundaries of network analysis, to broaden our understanding of plant defence against R. solanacearum.
A co-expression network compared how gene expression in S. lycopersicum and S. dulcamara responds to R. solanacearum inoculation at five time points post inoculation. This highlighted genes linked to the immune response which differ in expression between S. dulcamara and S. lycopersicum: Solyc10G001528, Solyc10G000984, Solyc05G001746, Solyc08G000580, Solyc11G001222, and Solyc01G003106. This stretched the capabilities of network analysis to incorporate both cross species and time series data, allowing for the identification of Differentially Expressed Genes (DEGs) related to immunity. Further work is required to mimic S. dulcamara’s expression of these genes in S. lycopersicum to assess whether their function regarding immunity can be transferred to reduce disease.
Additionally, a co-abundance network assessed the influence 2,6-dihydroxybenzoic acid (2,6-DHBA) - a metabolite extracted from S. dulcamara root exudates - has on the surrounding microbial communities and to both R. solanacearum infection and abundance. This work highlighted six taxa of interest that were influential in the network, and their links to disease have been theorised. However, further research into their roles in the specific interactions between 2,6-DHBA and R. solanacearum is required.
This broad study of resistance to R. solanacearum has shed light on a multitude of potential resistance mechanisms that S. dulcamara has evolved, hopefully contributing to a more sustainable quantitative approach to resistance in S. lycopersicum.