EFD Is an ERF transcription factor involved in the control of nodule number and differentiation in Medicago truncatula.
Mechanisms regulating legume root nodule development are still poorly understood, and very few regulatory genes have been cloned and characterized. Here, we describe EFD (for ethylene response factor required for nodule differentiation), a gene that is upregulated during nodulation in Medicago truncatula. The EFD transcription factor belongs to the ethylene response factor (ERF) group V, which contains ERN1, 2, and 3, three ERFs involved in Nod factor signaling. The role of EFD in the regulation of nodulation was examined through the characterization of a null deletion mutant (efd-1), RNA interference, and overexpression studies. These studies revealed that EFD is a negative regulator of root nodulation and infection by Rhizobium and that EFD is required for the formation of functional nitrogen-fixing nodules. EFD appears to be involved in the plant and bacteroid differentiation processes taking place beneath the nodule meristem. We also showed that EFD activated Mt RR4, a cytokinin primary response gene that encodes a type-A response regulator. We propose that EFD induction of Mt RR4 leads to the inhibition of cytokinin signaling, with two consequences: the suppression of new nodule initiation and the activation of differentiation as cells leave the nodule meristem. Our work thus reveals a key regulator linking early and late stages of nodulation and suggests that the regulation of the cytokinin pathway is important both for nodule initiation and development.
Vernié
Tatiana
T
Laboratoire des Interactions Plantes Micro-Organismes, Unité Mixte de Recherche, Centre National de la Recherche Scientifique-Institut National de la Recherche Agronomique 2594/441, F- 31320 Castanet Tolosan, France.
Moreau
Sandra
S
de Billy
Françoise
F
Plet
Julie
J
Combier
Jean-Philippe
JP
Rogers
Christian
C
Oldroyd
Giles
G
Frugier
Florian
F
Niebel
Andreas
A
Gamas
Pascal
P
D002467:Cell Nucleus / Q000378:metabolism; D003583:Cytokinins / Q000378:metabolism; D005030:Ethylenes / Q000378:metabolism; D025461:Feedback, Physiological; D017353:Gene Deletion; D020869:Gene Expression Profiling; D046913:Medicago truncatula / Q000166:cytology / Q000254:growth & development / Q000382:microbiology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009586:Nitrogen Fixation; D010802:Phylogeny; D010940:Plant Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D055170:Plant Root Nodulation / Q000502:physiology*; D034622:RNA Interference; D053204:Root Nodules, Plant / Q000166:cytology / Q000378:metabolism / Q000382:microbiology; D015398:Signal Transduction; D016962:Sinorhizobium meliloti / Q000502:physiology; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics / Q000502:physiology*
D003583:Cytokinins; D005030:Ethylenes; D010940:Plant Proteins; D014157:Transcription Factors; C036216:ethylene