Cytokinin as a mediator for regulating root system architecture in response to environmental cues.

Root system architecture (RSA) is developmentally controlled by genetic pathways and their interaction with various environmental cues, in particular soil conditions. One important player in shaping RSA is the hormone cytokinin, which acts as a negative regulator of root elongation and branching. The redundant roles of cytokinin metabolism and signaling genes of Arabidopsis thaliana in regulating early stages of lateral root formation has recently been shown and it has been proposed that this redundancy reflects a role in mediating different environmental cues. Here we report that the transcript levels of cytokinin genes in the root responds to changes in nutrient availability in distinct ways. IPT3, IPT5, CYP735A2, LOG5, and CKX4 are particularly responsive cytokinin metabolism genes, genes encoding different type-A response regulators and the transcriptions factor genes ARR10 and CRF6 are among the most responsive signaling genes. This finding supports the hypothesis that environmental cues operate through fine-tuned transcriptional regulation of cytokinin genes to modulate root development.