Two CCAAT box-binding transcription factors redundantly regulate early steps of the legume-rhizobia endosymbiosis

Tom Laloum, Maël Baudin, Lisa Frances, Agnes Lepage, Benjamin Billault-Penneteau, Marion R. Cerri, Federico Ariel, Marie-Françoise Jardinaud, Pascal Gamas, Fernanda de Carvalho-Niebel and Andreas Niebel

Résumé:

During endosymbiotic interactions between legume plants and nitrogen-fixing rhizobia, successful root infection by bacteria and nodule organogenesis requires the perception and transduction of bacterial lipo-chitooligosaccharidic signal called Nod Factor (NF). NF perception in legume roots leads to the activation of an early signaling pathway and of a set of symbiotic genes which is controlled by specific early transcription factors (TFs) including CYCLOPS/IPD3, NSP1, NSP2, ERN1 and NIN. In this study, we bring strong evidence that the Medicago truncatula CCAAT box-binding NF-YA1 TF, previously associated with later stages of rhizobial infection and nodule meristem formation is, together with its closest homolog NF-YA2, also an essential positive regulator of the NF signaling pathway. Here show that NF-YA1 and NF-YA2 are both expressed in epidermal cells responding to NFs and their knock-down by reverse genetic approaches severely affects the NF-induced expression of symbiotic genes and rhizobial infection. Further overexpression, transactivation and ChIP-PCR approaches indicate that NF-YA1 and NF-YA2 function, at least in part, via the direct activation of ERN1. We thus propose a model in which NF-YA1 and NF-YA2 appear as early symbiotic regulators acting downstream of DMI3 and NIN and possibly within the same regulatory complexes as NSP1/2 to directly activate the expression of ERN1.

Revue:

The plant journal

Lien:

onlinelibrary.wiley.com/doi/10.1111/tpj.12587/abstract