Abstract
BackgroundRadish (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 object Arabidopsis 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.ResultsIn present work we studied the role of CLE peptides in the development of storage root in radish. We have identified 18 CLE genes of radish (RsCLEs) and measured their expression in various plant organs and also at different stages of root development in R. sativus and Raphanus raphanistrum—its close relative which does not form storage root. We observed significant decline of expression levels for genes RsCLE1, 2, 11, 13, and 16, and also multifold increase of expression levels for genes RsCLE19, and 41 during secondary root growth in R. sativus but not in R. raphanistrum. Expression of RsCLE 2, 19, and 41 in R. sativus root was confined to certain types of tissues while RsCLE1, 11, 13, and 16 expressed throughout the root. Experiments on overexpression of RsCLE2, 19 and 41 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 of RsCLE2 and 19 strongly decrease in response to exogenous cytokinin, while auxin causes dramatic increase of RsCLE19 expression level and decrease of RsCLE41 expression.ConclusionsOur data allow us to hypothesize about the role of RsCLE2, 19 and 41 genes in the development of storage root of Raphanus sativus, e.g. RsCLE19 may play a role in auxin-dependent processes of xylem differentiation and RsCLE41 stimulates cambium activity.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0687-y) contains supplementary material, which is available to authorized users.
Highlights
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
Some Arabidopsis CLE peptides function as central regulators of apical and lateral primary meristems: in particular, CLV3 peptide is required for correct SAM development [9]; CLE40 has similar function in RAM [10]; CLE41/CLE44 controls the development of procambium and cambium [11]
In the present work we identified Raphanus sativus Raphanus sativus CLE (RsCLE) genes based on their homology with corresponding Arabidopsis thaliana AtCLE genes
Summary
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. It is accepted that functions of most CLE peptides in the meristems consist in the negative regulation of stem cell proliferation and thereby maintaining meristem size. An exception from this is a small group of TDIF (TRACHEARY ELEMENT DIFFERENTIATION INHIBITORY FACTOR)-like CLE peptides, which do not suppress cell proliferation in the meristems or even stimulate it in the procambium and cambium [7]. CLE peptides are supposed to regulate other developmental processes, like early embryogenesis [14] or vessel development [11, 15] Taking all of this into account, we can hypothesize that CLEs may function as regulators of storage root development in radish
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