Aggregated gene co-expression networks for predicting transcription factor regulatory landscapes in a non-model plant species
Gene co-expression networks (GCNs) have not been extensively studied in non-model plants. However, the rapid accumulation of transcriptome datasets in these species represents an opportunity to explore underutilized network aggregation approaches that highlight robust co-expression interactions and improve functional connectivity. We applied and evaluated two different aggregation methods on public grapevine RNA-Seq datasets belonging to three different tissue conditions (leaf, berry and 'all organs'). Our results show that co-occurrence-based aggregation generally yielded the best-performing networks. We applied GCNs to study several TF gene families, showing its capacity of detecting both already-described and novel regulatory relationships between R2R3-MYBs, bHLH/MYC and multiple secondary metabolism pathway reactions. Specifically, using TF gene- and pathway-centered network analyses, we ascertained the previously demonstrated role of VviMYBPA1 in controlling the accumulation of proanthocyanidins while providing novel insights into its role as a potential regulator of p-coumaroyl-CoA biosynthesis as well as the shikimate and aromatic amino-acid pathways. This network was validated using DNA Affinity Purification Sequencing data, demonstrating that co-expression networks of activational transcription factors can serve as a proxy of gene regulatory networks. This study presents an open repository to reproduce networks and a GCN application within the Vitviz platform, a user-friendly tool for exploring co-expression relationships. Overall design: Identification of binding sites for MYBPA1 transcription factor in Vitis vinifera by direct sequencing of affinity purified genomic DNA fragments.