Harkey, A. F.; Khoury, M. G.; Muhlemann, J. K.; Olex, A. L.; Houben, M.; Binder, B.; Muday, G. K.

In Arabidopsis, a family of five receptors mediates ethylene responses in distinct tissues and cell types, with Ethylene Response 1 (ETR1) controlling ethylene-mediated increases in root hair proliferation and decreases in lateral root formation. To define the ETR1-dependent gene regulatory network (GRN) controlling root development, we profiled the transcriptome of roots from Col-0 seedlings and the etr1-3 gain-of-function and etr1-7 loss-of-function mutants in the presence and absence of ethylene or ACC treatment after 1, 4, and 24 hours. We identified 4,522 DE transcripts in Col-0 roots whose abundance changed in response to ethylene and/or ACC treatment with larger magnitude changes induced by ethylene. There were 961 genes regulated similarly by both treatments in at least one time point . We identified 553 transcripts that were ETR1-dependent, defined by the absence of response to ethylene and/or ACC treatment in the ethylene-insensitive etr1-3 mutant and altered transcript abundance in the constitutive-signaling etr1-7 mutant in the absence of ethylene and/or ACC relative to untreated Col-0. Six ETR1-dependent transcripts are predicted to encode transcription factors: ANAC058, LRP1, MYB9, MYB52, MYB93, and RAP2.6L. We examined ACC-modulated root development in plants with mutations in these genes, revealing roles of these proteins in regulating root development. Using published TF target data, we found TFs that are both EIN3-regulated and EIN3-independent with members of both groups regulating root development. Together, these findings reveal features of an ETR1-dependent GRN controlling root growth and development.