Abstract
Agrobacterium rhizogenes root oncogenic locus B (rolB) is known to induce hairy roots along with triggering several physiological and morphological changes when present as a transgene. However, it is still unknown how this gene triggers these changes within the plant system. In this study, the effect of rolB in-planta, when present as a transgene, was assessed on the gene expression levels of auxin response factors (ARFs)-transcription factors which are key players in auxin-mediated responses. The goal was to uncover Auxin/ARF-driven transcriptional networks potentially active and working selectively, if any, in rolB transgenic background, which might potentially be associated with hairy root development. Hence, the approach involved establishing rolB-transgenic Nicotiana tabacum plants, selecting ARFs (NtARFs) for context-relevance using bioinformatics followed by gene expression profiling. It was observed that out of the chosen NtARFs, NtARF7 and NtARF19 exhibited a consistent pattern of gene upregulation across organ types. In order to understand the significance of these selective gene upregulation, ontology-based transcriptional network maps of the differentially and nondifferentially expressed ARFs were constructed, guided by co-expression databases. The network maps suggested that NtARF7-NtARF19 might have major deterministic, underappreciated roles to play in root development in a rolB-transgenic background-as observed by higher number of "root-related" biological processes present as nodes compared to network maps for similarly constructed other non-differentially expressed ARFs. Based on the inferences drawn, it is hypothesized that rolB, when present as a transgene, might drive hairy root development by selective induction of NtARF7 and NtARF19, suggesting a functional link between the two, leading to the specialized and characteristic rolB-associated traits.