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Science Signaling  23 Nov 2010:
Vol. 3, Issue 149, pp. ec354
DOI: 10.1126/scisignal.3149ec354

In Arabidopsis roots, cells proliferate in a region called the meristem, and they expand in volume and begin to differentiate in the elongation zone. Tsukagoshi et al. (see also Wells et al.) used gene expression data to identify transcription factors in Arabidopsis that show high abundance in the transition zone, the boundary between the meristem and elongation zone. upb1-1 plants, which had a mutation that reduced the abundance of transcription factor UPBEAT1 (UPB1), had longer roots and more cortex cells in the meristem than wild-type plants. In contrast, three lines that overexpressed UPB1 had shorter roots and fewer cortex cells in the meristem than wild-type plants. Fluorescently tagged UPB1 localized predominantly to the elongation zone. Direct transcriptional targets of UPB1 included three genes encoding peroxidases (PER39, PER40, and PER57) with high abundance in the transition zone, like UPB1. UPB1 repressed the expression of the genes encoding these peroxidases, because their abundance was increased in upb1-1 mutant plants and decreased in UPB1-overexpressing plants. Furthermore, plants overexpressing PER57 had larger meristems than wild-type plants. Treatment with H2O2 decreased meristem and root length in wild-type plants but not in upb1-1 or UPB1-overexpressing plants. In contrast, treatment with an H2O2 scavenger increased meristem and root length in wild-type and UPB1-overexpressing plants but not in upb1-1 plants. Inhibition of peroxidase activity reduced meristem size in wild-type and upb1-1 plants but not in UPB1-overexpressing plants. In wild-type plants, H2O2 concentrations were higher in the elongation zone than in the meristem. In contrast, concentrations of superoxide (O2•–), which is generated by NADPH oxidases, were higher in the meristem than in the elongation zone and were increased in upb1-1 mutants and decreased in UPB1-overexpressing plants. The UPB1 pathway appeared to act independently of cytokinin and auxin, two signaling pathways involved in regulating root length. Thus, UPB1 exerts transcriptional control over the formation of gradients of reactive oxygen species in Arabidopsis root, which determines the transition between the meristematic and elongation zones and thus between cellular proliferation and differentiation.

H. Tsukagoshi, W. Busch, P. N. Benfey, Transcriptional regulation of ROS controls transition from proliferation to differentiation in the root. Cell 143, 606–616 (2010). [PubMed]

D. M. Wells, M. H. Wilson, M. J. Bennett, Feeling UPBEAT about growth: Linking ROS gradients and cell proliferation. Dev. Cell 19, 644–646 (2010). [PubMed]

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