Overexpression of the Ib-rolB/C gene perturbs biosynthesis of caffeoylquinic acid derivatives in transgenic calli of sweet potato

Ipomoea batatas is a root crop widely cultivated in South America, Africa, and Asia. This is also a source of caffeoylquinic acid derivatives (CQAs) with potential health-promoting benefits. Sweet potato genome carries two separate cellular T-DNA (cT-DNA) regions (IbT-DNA1 and IbT-DNA2). Especially, IbT-DNA2 contains five ORFs homologous to the Agrobacterium rhizogenes T-DNA, namely ORF13, ORF14, ORF17n, ORF18/ORF17n, and RolB/RolC proteins [1]. Unfortunately, presently there is insufficient information on IbT-DNA2 genes function in the physiological processes of sweet potatoes. 
In this study, expressional levels of the IbT-DNA2 genes and the effect of Ib-rolB/C overexpression were examined using I. batatas cell culture. We discovered that I. batatas cT-DNA genes were not expressed in callus, and abiotic stresses and chemical elicitors affected their transcriptional levels weakly. Additionally, two Ib-rolBC-transgenic cell lines have been established though Agrobacterium-mediated transformation of I. batatas callus cells. Overexpression of Ib-rolB/C gene reduced biomass accumulation of transgenic cell lines by 1.21.6 times and increased the CQAs content by 1.51.9-fold. To justify the metabolic fluctuations, the study also looked into the expression patterns of the major biosynthetic genes, namely bPAL, IbC4H, Ib4CL, IbHCT, and IbHQT. The obtained data demonstrated that the overexpression of the Ib-rolB/C reduced the IbPAL transcript but considerable increase in the transcript levels of the IbHQT. We propose that this result was obtained through as-yet-uncharacterized signaling pathways activated by RolB/RolC.