| Cytokinins are N6-substituted adenine derivatives that play diverse roles in plant growth and development, including meristem function, leaf senescence, sink/source distribution, vascular development and (a)biotic stress responses (1). Dirigent proteins (DIRs) have been found to mediate regio- and stereo-specific monolignol coupling during formation of lignans that might serve as (a)biotic stress-delimiting plant ‘biological weapons’ (2). The presence of DIR protein epitopes in lignifying tissues and lignin initiation sites provided the basis for the hypothesis that DIRs guide regio- and stereo-specificity not only of lignans, but of the lignin, as well (3). Root endodermis differentiation involves formation of the Casparian Strip (CS), an apoplastic barrier analogous to animal endodermal tight-junctions, consisting of a ring-like impregnation of the primary cell wall with lignin (3). EBS1/DIR10 was shown to mediate CS formation via precise targeting of the lignification-mediating complex (4). Members of the DIR family were suggested to be direct targets of cytokinin signaling (5). We propose that cytokinin can control the cell wall composition and/or properties possibly in a response to abiotic stresses or as a part of developmental regulations via regulation of dirigent genes AtDIR13. REFERENCES 1. Bhargava A., Clabaugh I., To J.P., Maxwell B. B., Chiang Y.-H., Schaller G. E., Loraine A., Kieber J. J.: Plant Physiology_, Vol. 162, pp. 272–294 (2013). 2. Davin L. B., Wang H. B., Crowell A. L., Bedgar D. L., Martin D. M., Sarkanen S., Lewis N. G.: Science 275 (5298), (1997). 3. Barbosa I.C.R, Rojas-Murcia N., Geldner N.: Current Opinion in Biotechnology, 56:121–129 (2019). 4. Hosmani, P. S., Kamiya T., Danku J., Naseer S., Geldner N., Guerinot M. L. Salt D. E.: Proc Natl Acad Sci U S A 110, 14498-14503 (2013). |
