Aluminum-induced terminal differentiation in Arabidopsis roots requires the stem cell niche transcription factor ETHYLENE RESPONSE FACTOR 115

Aluminum-dependent stoppage of root growth and terminal differentiation depend on a functional DNA damage response pathway comprised of the master cell cycle checkpoint ATR (ATAXIA TELANGIECTASIA-MUTATED AND RAD3-RELATED) and p53-like transcription factor SOG1 (SUPPRESSOR OF GAMMA RADIATION 1). Mutational loss of either results in failure to trigger endoreduplication following Al treatment even in the Al-hypersensitive mutant, als3-1. Transcriptome analyses were used to identify several Al-induced SOG1-regulated targets as candidate mediators of Al-dependent growth arrest including SMR5, SMR7, ERF114 and ERF115. Analysis of these factors either as loss-of-function/silenced mutants or by overexpression in the als3-1 background indicates ERF115, a key transcription factor involved in stem cell niche restoration, is important for the switch from an actively growing root to one that has terminally differentiated. Consistent with this, a putative ERF115 ortholog and other DDR factors from barley are also upregulated following Al exposure, suggesting a conserved role for this ATR-dependent pathway in response to Al. In contrast to other ts show that ERF115 and related family members are important determinants for the switch to endoreduplication in the root tip following Al exposure and a central output of the ATR-mediated pathway in Al response. SOG1 is a transcription factor that is part of the Al-triggered DDR and is required for terminal differentiation of the root, it is expected that one or more transcriptional target(s) of SOG1 mediate this developmental switch from normal cell cycle progression to endocycling. In order to identify this type of SOG1 targets, an RNAseq approach was undertaken to compare transcript profiles of Al-treated Columbia-0 (Col-0) wt, als3-1 and sog1-7, which is a previously documented loss-of-function mutant for SOG1 that is Al tolerant (Sjogren et al., 2015). Comparison of transcript profiles for als3-1 and sog1-7 following Al treatment has allowed us to greatly reduce the number of potential genes related to stoppage of root growth following Al exposure.