The DNA Binding Site of the Dof Protein NtBBF1 Is Essential for Tissue-Specific and Auxin-Regulated Expression of the rolB Oncogene in Plants

Abstract

The Dof proteins are a large family of plant transcription factors that share a single highly conserved zinc finger. The tobacco Dof protein NtBBF1 was identified by its ability to bind to regulatory domain B in the promoter of the rolB oncogene. In this study, we show that the ACT TTA target sequence of NtBBF1 in domain B is necessary for tissue-specific expression of rolB . ␤ -Glucuronidase (GUS) activity of tobacco plants containing a rolB promoter-GUS fusion with a mutated NtBBF1 target sequence within domain B is almost completely suppressed in apical meristems and is severely abated in the vascular system. The ACTTTA motif is shown here also to be one of the cis -regulatory elements involved in auxin induction of rolB . The pattern of NtBBF1 expression in plants is remarkably similar to that of rolB , except in mesophyll cells of mature leaves, in which only NtBBF1 expression could be detected. Ectopic expression of rolB in mesophyll cells was achieved by particle gun delivery if the NtBBF1 binding sequence was intact. These data provide evidence that in the plant, a Dof protein DNA binding sequence acts as a transcriptional regulatory motif, and they point to NtBBF1 as the protein involved in mediating tissue-specific and auxin-inducible expression of rolB . INTRODUCTIONInfection of dicotyledonous plants with Agrobacterium rhizogenes results in hairy root disease (Elliot, 1951). Hairy root causes an abundant proliferation of neoplastic roots containing T-DNA from the root-inducing (Ri) bacterial plasmid (Chilton et al., 1982;Spanò et al., 1982;White et al., 1982;Willmitzer et al., 1982). In the T-DNA sequence, 18 open reading frames have been identified (Slightom et al., 1986). Four of these, termed the rol oncogenes, coincide with genetic loci previously localized by transposon mutagenesis (White et al., 1985). Among the rol oncogenes, rolB is the only one that, when inactivated, totally suppresses root induction by A. rhizogenes (White et al., 1985). In addition, rolB is the only individual gene capable of inducing growth of transformed roots for all plants tested (Cardarelli et al., 1987;Spena et al., 1987;Capone et al., 1989). More recently, in cultured thin cell layers ( Tran Thanh Van et al., 1974), the stimulation of meristem formation has been shown to be the primary effect of rolB (Altamura et al., 1994). Expression of rolB greatly increases the sensitivity of transformed plant cells to auxin (Spanò et al., 1988;Maurel et al., 1991), and tyrosine phosphatase activity has been associated with the RolB protein when it is expressed in Escherichia coli (Filippini et al., 1996), suggesting that RolB may act by perturbing the auxin signal transduction pathway.The expression of rolB in transgenic plants also has been extensively analyzed and found to be strongest in root and shoot meristems (Schmülling et al., 1989;Maurel et al., 1990;Altamura et al., 1991;Capone et al., 1991), which is in accord with an effect of the oncogene on meristem induction. Expression was also detectable in the vascular system....

SlARF4, an Auxin Response Factor Involved in the Control of Sugar Metabolism during Tomato Fruit Development

“…In silico analysis of the 1.8-kb promoter sequence performed using the PLACE signal scan search tool (http://www.dna.affrc.go.jp/PLACE/ signalscan.html) identified several cis-elements, including the canonical auxin response element (AuxRE), TGTCTC, at position -220, a sugar starvation element, TATCCA, at position -960, and an auxin induction element, ACTTTA, at position -977. This latter sequence has been shown to be involved in mediating tissuespecific and auxin-inducible expression of the rolB oncogene (Baumann et al, 1999).…”

Constitutive overexpression of GmDof17-1, a putative DOF transcription factor from soybean causing growth inhibition in tobacco

“…Many authors have noted the relationships between Dof transcription factors and hormone signaling, such as NtBBF1 and auxin in tobacco, AOBP and auxin in pumpkin and OBP3 and salicylic acid in Arabidopsis (Baumann et al, 1999;De Paolis et al, 1996;Kang and Singh, 2001;Kang et al, 2000;Kisu et al, 1998;Ward et al, 2005). In Arabidopsis thaliana, the Dof protein DAG1 mediates PIL5 activity during seed germination by negatively regulating the GA biosynthetic gene (Gabriele et al, 2010).…”

“…Some researchers have studied the interactions between Dof proteins and phytohormones and the tobacco Dof protein NtBBF1 has been found to be involved in the auxin-inducible expression of rolB (Baumann et al, 1999).…”

“…Since Dof1 (the fi rst identifi ed Dof protein) was found in maize (Yanagisawa and Izui, 1993), many Dof proteins have been discovered, which participate in specifi c biological processes in other plants. The functions of reported Dof genes are highly diverse and include roles in hormone response, defense response, organ development and other responses (Baumann et al, 1999;Kang and Singh, 2001; Kang et al, 2000;Kisu et al, 1998;Mena et al, 1998;Plesch et al, 2001;Vicente-Carbajosa et al, 1997;Wang et al, 2007;Ward et al, 2005;Washio, 2001;Xin et al, 2009;Yang et al, 2010).…”

“…Since Dof1 (the fi rst identifi ed Dof protein) was found in maize (Yanagisawa and Izui, 1993), many Dof proteins have been discovered, which participate in specifi c biological processes in other plants. The functions of reported Dof genes are highly diverse and include roles in hormone response, defense response, organ development and other responses (Baumann et al, 1999;Kang and Singh, 2001; Kang et al, 2000;Kisu et al, 1998;Mena et al, 1998;Plesch et al, 2001;Vicente-Carbajosa et al, 1997;Wang et al, 2007;Ward et al, 2005;Washio, 2001;Xin et al, 2009;Yang et al, 2010).Phytohormones play important roles in coordinating many growth-related processes throughout the plant life cycle, including embryogenesis, vascular differentiation, organogenesis, tropic growth and root and shoot architecture (Kepinski, 2006;Quint and Gray, 2006; Shan et al, 2012 Stamm andKumar, 2010). Some researchers have studied the interactions between Dof proteins and phytohormones and the tobacco Dof protein NtBBF1 has been found to be involved in the auxin-inducible expression of rolB (Baumann et al, 1999).…”