Gibberellins (GA) and cytokinins - plant hormones - induce antagonistic signals during leaf formation and in meristem maintenance. Both hormone signalling pathways are required in Arabidopsis for the initiation of their defensive epidermal structures, trichomes. GA act via the transcription factor (TF) GLABROUS INFLORESCENCE STEMS (GIS). The downstream mechanisms by which cytokinin signalling regulates this process are less clear. Now, Pierre Broun's group show that the GIS-related transcription factors GIS2 and ZFP8,but not GIS, mediate this response to cytokinins(). A series of overexpression and RNAi-knockdown experiments in both wild-type and mutant plants reveal that GIS, GIS2 and ZFP8 play overlapping roles in GA signalling,but that GIS is dispensable for cytokinin signalling. The molecular interactions between the two hormone signalling pathways are thus uncovered and, interestingly, despite shared mechanisms of action, these TFs have evolved differential responses to GA and cytokinin signalling.
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