Poster: Hormones

Abs # 567: Arabidopsis RRD4: A negative regulator of negative effects of cytokinin

Presenter:	Sugiyama, Munetaka , sugiyama@ns.bg.s.u-tokyo.ac.jp
Authors	Sugiyama, Munetaka  (A)   Togami, Jun-ichi  (A)   Koizumi, Koji  (A)   Nagawa, Shingo  (A)   Nagamiya, Kenji  (A)
Affiliations:	(A): Botanical Gardens, Graduate School of Science, The University of Tokyo

For the purpose of identifying essential machineries of plant development genetically, we have isolated and characterized many mutants of Arabidopsis thaliana that are temperature sensitive for various aspects of in-vitro organogenesis. Here we report research results on one of these mutants, rrd4. Screening of an EMS-mutagenized population of arabidopsis with callus-mediated root redifferentiation as an index phenotype resulted in isolation of three temperature-sensitive mutants, rrd1, rrd2, and rrd4. Examination of tissue culture responses of the rrd4 mutant showed that it exhibited a severe defect of dedifferentiation (more strictly speaking, acquisition of competence with respect to cell proliferation) and a leaky defect of cell proliferation in a cytokinin-dependent manner at the restrictive temperature. This implies that the RRD4 gene product functions in sequestering negative actions of cytokinin on dedifferentiation and cell proliferation, which are normally observed only at high concentrations of cytokinin. Positional cloning of the RRD4 gene revealed that it corresponds to At1g17070 and encodes a G-patch-containing protein very similar to mouse tuftelin-interacting protein (TIP39) and Drosophila septin-interacting protein (SIP1).