AP2-ERF transcription factors mediate Nod factor dependent Mt ENOD11 activation in root hairs via a novel cis-regulatory motif.
Rhizobium Nod factors (NFs) are specific lipochitooligosaccharides that activate host legume signaling pathways essential for initiating the nitrogen-fixing symbiotic association. This study describes the characterization of cis-regulatory elements and trans-interacting factors that regulate NF-dependent and epidermis-specific gene transcription in Medicago truncatula. Detailed analysis of the Mt ENOD11 promoter using deletion, mutation, and gain-of-function constructs has led to the identification of an NF-responsive regulatory unit (the NF box) sufficient to direct NF-elicited expression in root hairs. NF box-mediated expression requires a major GCC-like motif, which is also essential for the binding of root hair-specific nuclear factors. Yeast one-hybrid screening has identified three closely related AP2/ERF transcription factors (ERN1 to ERN3) that are able to bind specifically to the NF box. ERN1 is identical to an ERF-like factor identified recently. Expression analysis has revealed that ERN1 and ERN2 genes are upregulated in root hairs following NF treatment and that this activation requires a functional NFP gene. Transient expression assays in Nicotiana benthamiana have further shown that nucleus-targeted ERN1 and ERN2 factors activate NF box-containing reporters, whereas ERN3 represses ERN1/ERN2-dependent transcription activation. A model is proposed for the fine-tuning of NF-elicited gene transcription in root hairs involving the interplay between repressor and activator ERN factors.
Andriankaja
Andry
A
Laboratory of Plant Microbe Interactions, Centre National de la Recherche Scientifique-Institut National de la Recherche Agronomique, BP 52627, Castanet-Tolosan Cedex, France.
Boisson-Dernier
Aurélien
A
Frances
Lisa
L
Sauviac
Laurent
L
Jauneau
Alain
A
Barker
David G
DG
de Carvalho-Niebel
Fernanda
F
D000595:Amino Acid Sequence; D020029:Base Pairing; D001483:Base Sequence; D002467:Cell Nucleus / Q000378:metabolism; D017124:Conserved Sequence; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D046913:Medicago truncatula / Q000235:genetics*; D008957:Models, Genetic; D008969:Molecular Sequence Data; D019441:Plant Epidermis / Q000166:cytology / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D021381:Protein Transport; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D014026:Nicotiana / Q000166:cytology; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques; D015854:Up-Regulation