Résumé
Until recently, the roles of plant MADS-box genes have mainly been characterized duringinflorescence and flower dierentiation. In order to precise the roles of AGAMOUS-LIKE 12, one of thefew MADS-box genes preferentially expressed in roots, we placed its cDNA under the control of thedouble 35S CaMV promoter to produce transgenic walnut tree and Arabidopsis plants. In Juglans sp.,transgenic somatic embryos showed significantly higher germination rates but abnormal developmentof their shoot apex prevented their conversion into plants. In addition, a wide range of developmentalabnormalities corresponding to ectopic root-like structures aected the transgenic lines suggestingpartial reorientations of the embryonic program toward root dierentiation. In Arabidopsis, AtAGL12overexpression lead to the production of faster growing plants presenting dramatically wider andshorter root phenotypes linked to increased meristematic cell numbers within the root apex. In theupper part of the roots, abnormal cell divisions patterns within the pericycle layer generated largeectopic cell masses that did not prevent plants to grow. Taken together, our results confirm in bothspecies that AGL12 positively regulates root meristem cell division and promotes overall root vasculartissue formation. Genetic engineering of AGL12 expression levels could be useful to modulate rootarchitecture and development.