Identification, expression, and functional analysis of CLE genes in radish (Raphanus sativus L.) storage root. Issue 1 (January 2016) - Gancheva, Maria
Abstract Background Radish (Raphanus sativus L.) is a widespread agricultural plant forming storage root due to extensive secondary growth which involves cambium proliferation and differentiation of secondary conductive tissues. Closely related to the model objectArabidopsis thaliana, radish is a suitable model for studying processes of secondary growth and storage root development. CLE peptides are a group of peptide phytohormones which play important role in the regulation of primary meristems such as SAM, RAM, and procambium, as well as secondary meristems. However, the role of CLE peptides in lateral growth of root during storage root formation has not been studied to date. Results In present work we studied the role of CLE peptides in the development of storage root in radish. We have identified 18CLE genes of radish (RsCLEs ) and measured their expression in various plant organs and also at different stages of root development inR. sativus andRaphanus raphanistrum —its close relative which does not form storage root. We observed significant decline of expression levels for genesRsCLE1, 2, 11, 13, and16, and also multifold increase of expression levels for genesRsCLE19, and41 during secondary root growth inR. sativus but not inR. raphanistrum . Expression ofRsCLE 2, 19, and41 inR. sativus root was confined to certain types of tissues whileRsCLE1, 11, 13, and16 expressed throughout the root. Experiments on overexpression ofRsCLE2, 19 and41 or treatment of radish plants with synthetic CLE peptides revealed that CLE19 and CLE2 increase the number of xylem elements, and CLE41 induces the formation of extra cambium foci in secondary xylem. Expression levels ofRsCLE2 and19 strongly decrease in response to exogenous cytokinin, while auxin causes dramatic increase ofRsCLE19 expression level and decrease ofRsCLE41 expression. Conclusions Our data allow us to hypothesize about the role ofRsCLE2, 19 and41 genes in the development of storage root ofRaphanus sativus, e.g.RsCLE19 may play a role in auxin-dependent processes of xylem differentiation andRsCLE41 stimulates cambium activity.