Abstract
rrd4 is a temperature-sensitive mutant of Arabidopsis thaliana. It exhibits a severe defect of dedifferentiation and a leaky defect of cell proliferation in a cytokinin-dependent manner at the restrictive temperature. This feature 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. The RRD4 gene encodes an unknown protein containing a G-patch domain.
In this study, we re-examined cytokinin effects on the rrd4 phenotypes at various temperature. At 25C, interestingly, root elongation of rrd4 mutant was inhibited in the absence of exogenous cytokinin and recovered by adding low concentrations of cytokinin. The result indicates that the rrd4 mutation decreased sensitivity to endogenous cytokinin required for root growth. Gathering all the results together, we can assume that RRD4 elevates the positive action of cytokinin to counteract the negative effect of cytokinin.
