Rosmarinic acid (RA) is one of the first secondary metabolites produced in plant cell cultures in extremely high yields, up to 19% of the cell dry weight. More complex derivatives of RA, such as rabdosiin and lithospermic acid B, later were also obtained in cell cultures at high yields. RA and its derivatives possess promising biological activities, such as improvement of cognitive performance, prevention of the development of Alzheimer's disease, cardioprotective effects, reduction of the severity of kidney diseases and cancer chemoprevention. The TNF-α-induced NF-κB signaling pathway has emerged as a central target for RA. Despite these impressive activities and high yields, the biotechnological production of these metabolites on an industrial scale has not progressed. We summarized data suggesting that external stimuli, the Ca(2+)-dependent NADPH oxidase pathway and processes of protein phosphorylation/dephosphorylation are involved in the regulation of biosynthesis of these substances in cultured plant cells. In spite of growing information about pathways regulating biosynthesis of RA and its derivatives in cultured plant cells, the exact mechanism of regulation remains unknown. We suggest that further progress in the biotechnology of RA and its derivatives can be achieved by using new high-throughput techniques.

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Expression of rol agrobacterial oncogenes in plant cell cultures is known to result in activation of secondary metabolite biosynthesis. In the present work, we show that rolC can activate expression of key genes of secondary metabolism using the rolC-transgenic culture of Eritrichium sericeum producing caffeic acid metabolites (rosmarinic acid and rabdosiin) as an example. Increased content of rosmarinic acid in the rolC-transformed callus culture resulted from transcriptional activation of members of the CYP98 family of plant cytochrome P450-containing monooxygenase genes. The rolC gene expression led to increased transcript abundance of the CYP98A3 subfamily members, which are closely related homologs of CYP98A6 of Lithospermum erythrorhizon and are known to be key genes in rosmarinic acid biosynthesis. In contrast, expression of other CYP genes, such as CYP98A1 and CYP98A2, which are not implicated in rosmarinic acid biosynthesis, was not activated in the rolC-transformed calluses. These results are indicative of selective effect of rolC on transcription of particular genes implicated in secondary metabolism.

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