The BREVIS RADIX (BRX) domain was characterised as being a transcription factor in plants regulating the extent of cell proliferation and elongation in the growth zone of the root [1,2]. BRX is rate limiting for auxin-responsive gene-expression by mediating cross-talk with the brassino-steroid pathway. BRX has a ubiquitous, although quantitatively variable role in modulating the growth rate in both the root and the shoot [3]. This family features a short region, also alpha-helical, N-terminal to the repeated alpha-helices of family BRX, Pfam:PF08381 [1]. BRX is expressed in the vasculature and is rate-limiting for transcriptional auxin action [4].

1: Natural genetic variation in Arabidopsis identifies BREVIS RADIX, a novel regulator of cell proliferation and elongation in the root. Mouchel CF, Briggs GC, Hardtke CS; Genes Dev. 2004;18:700-714. PMID:15031265

2: Characterization of the plant-specific BREVIS RADIX gene family reveals limited genetic redundancy despite high sequence conservation. Briggs GC, Mouchel CF, Hardtke CS; Plant Physiol. 2006;140:1306-1316. PMID:16514016

3: BRX promotes Arabidopsis shoot growth. Beuchat J, Scacchi E, Tarkowska D, Ragni L, Strnad M, Hardtke CS; New Phytol. 2010;188:23-29. PMID:20649916

4: Spatio-temporal sequence of cross-regulatory events in root meristem growth. Scacchi E, Salinas P, Gujas B, Santuari L, Krogan N, Ragni L, Berleth T, Hardtke CS; Proc Natl Acad Sci U S A. 2010;107:22734-22739. PMID:21149702