The plant CDK inhibitor NtKIS1a interferes with dedifferentiation, is specifically down regulated during development and interacts with a JAB1 homolog

CKIs from plant and animal share functional similarities although their roles have evolved in each kingdom to become adapted to the specific requirement of developmental programs. In plants, two types of CKI have been described so far and only one is related to a limited extend to the animal p27KIP1 a fact essentially based on sequence similarities and interacting partners. To decipher the role of plant CKIs, a gain of function approach was mainly applied in Arabidopsis thaliana and showed that overexpressed CKIs inhibit cell division in planta. Here, Arabidopsis overexpressing NtKIS1a, a tobacco CKI, was used to address the question of how accumulation of the CDK/cyclin complex inhibitor NtKIS1a still allowed the development of a mature plant. We analysed the re-induction of division from differentiated cells and showed that NtKIS1a overexpression interfered with dedifferentiation. In order to test whether some discrete cells could get depleted of the inhibitory NtKIS1a protein, we analysed the presence of NtKIS1a protein in the various plant meristems. Surprisingly, its absence was revealed in the vegetative apical meristem. Characterisation of an interaction between NtKIS1a and AtAJH1, a plant JAB1 homolog, suggested that like p27KIP1, AtAJH1 might target NtKIS1a degradation. Furthermore, NtKIS1a sub-cellular localisation was modified in the presence of AtAJH1.