A barley gene encoding a novel DNA-binding protein (HRT) was first identified by southwestern screening with baits containing a gibberellin phytohormone response element from an α-amylase promoter. Zinc and DNA binding assays demonstrate that HRT contains three unusual zinc fingers with a CX8-9CX10CX2H consensus sequence (Interpro IPR038909). In vivo, functional tests in plant cells indicate that full length HRT can repress expression from certain promoters including the Amy1/6-4 andAmy2/32 α-amylase promoters. In contrast, truncated forms of HRT containing DNA-binding domains can activate, or derepress, transcription from these promoters (Raventos et al., 1998, PMID: 9722564).  In later studies on plant plant embryogenesis, similar proteins with two to five C-terminal DNA- and Zn-binding repeats were discovered and named EFFECTOR OF TRANSCRIPTION (ET) (Ellerstrom et al., 2005, Ivanov et al., 2008, PMID: 16244914, PMID: 17991462). ETs also share a characteristic DNA single‐strand nuclease domain (GIY‐YIG) with structural similarity to that of bacterial UVRC proteins and homing nucleases.

In Arabidopsis there are three ETs. AtET2 plays a role in the regulation of plant hormone GA (gibberellin) and cell-cycle-related protein GASA4. Regulation of GA response has also been observed in Brassica napus ET, and could be a conserved feature of these proteins.  In Arabidopsis, comparative DNA methylation and transcriptome analyses in flowers and seedlings of et mutants revealed ET-specific differentially expressed genes and mostly independently characteristic, ET-specific differentially methylated regions. Loss of ET function results in pleiotropic developmental defects. The accumulation of cyclobutane pyrimidine dimers after ultraviolet stress in et mutants suggests an ET function in DNA repair (Tedeschi et al., 2019, PMID: 30252137).  When Brassica napus (BnET) is ectopically expressed in either Arabidopsis or tobacco the phenotypes include dwarfism due to shorter internodes and late flowering, reduced germination rate, increased anthocyanin content and reduced xylem lignification as a marker for terminal cell differentiation (Ellerstrom et al., 2005, PMID: 16244914).  At least one HRT or ET related TF appears to be present in maize (Zm00001eb325970).

Last updated June 2023 by John Gray

References:

Raventós D, Skriver K, Schlein M, Karnahl K, Rogers SW, Rogers JC, Mundy J. HRT, a novel zinc finger, transcriptional repressor from barley. J Biol Chem. 1998 Sep 4;273(36):23313-20. doi: 10.1074/jbc.273.36.23313. PMID: 9722564.

Ellerström M, Reidt W, Ivanov R, Tiedemann J, Melzer M, Tewes A, Moritz T, Mock HP, Sitbon F, Rask L, Bäumlein H. Ectopic expression of EFFECTOR OF TRANSCRIPTION perturbs gibberellin-mediated plant developmental processes. Plant Mol Biol. 2005 Nov;59(4):663-81. doi: 10.1007/s11103-005-0669-9. PMID: 16244914.

Ivanov R, Tiedemann J, Czihal A, Schallau A, Diep le H, Mock HP, Claus B, Tewes A, Bäumlein H. EFFECTOR OF TRANSCRIPTION2 is involved in xylem differentiation and includes a functional DNA single strand cutting domain. Dev Biol. 2008 Jan 1;313(1):93-106. doi: 10.1016/j.ydbio.2007.09.061. Epub 2007 Oct 11. PMID: 17991462.

Ivanov R, Tiedemann J, Czihal A, Baumlein H. Transcriptional regulator AtET2 is required for the induction of dormancy during late seed development. Journal of Plant Physiology. 2012 Mar;169(5):501-508. DOI: 10.1016/j.jplph.2011.11.017. PMID: 22226340.

Tedeschi F, Rizzo P, Huong BTM, Czihal A, Rutten T, Altschmied L, Scharfenberg S, Grosse I, Becker C, Weigel D, Bäumlein H, Kuhlmann M. EFFECTOR OF TRANSCRIPTION factors are novel plant-specific regulators associated with genomic DNA methylation in Arabidopsis. New Phytol. 2019 Jan;221(1):261-278. doi: 10.1111/nph.15439. Epub 2018 Sep 25. PMID: 30252137; PMCID: PMC6585611.