Cell shape can be uncoupled from formononetin induction in a novel cell line from Callerya speciosa

It is the first time that formononetin produced by cell culture and its accumulation was shown to be triggered by specific stress signalling linked jasmonate pathway. Callerya speciosa, an endangered traditional Chinese medicine plant, is intensively used in traditional folk medicine. To develop sustainable alternatives for the overexploitation of natural resources, a suspension cell line was created from C. speciosa. Ingredients of C. speciosa, for instance the isoflavone formononetin, are formed during a peculiar swelling response of the root, which is considered as a quality trait for commercial application. A cell strain with elongated cells was obtained by using synthetic cytokinin 6-benzylaminopurine (6-BA) and synthetic auxin picloram. Both, picloram and 6-BA, promote cell division, whereas picloram was shown to be crucial for the maintenance of axial cell expansion. We addressed the question, whether the loss of axiality observed in the maturating root is necessary and sufficient for the accumulation of formononetin. While we were able to mimic a loss of axiality for cell expansion, either by specific combinations of 6-BA and picloram, or by treatment with the anti-microtubular compound oryzalin, formononetin was not detectable. However, formononetin could be induced by the stress hormone methyl jasmonate (MeJA), as well as by the bacterial elicitor flagellin peptide (flg22), but not by a necrosis inducing protein. Combined the fact that none of these treatments induced the loss of axiality, we conclude that formononetin accumulates in response to basal defence and unrelated with cell swelling.