DELLA-mediated gibberellin signalling regulates Nod factor signalling and rhizobial infection.

Camille Fonouni-Farde,Florian Frugier,Jiangqi Wen,Mathias Brault,Maël Baudin,Anouck Diet,Kirankumar S Mysore,Andreas Niebel,Sovanna Tan

doi:10.1038/ncomms12636

Abstract

Legumes develop symbiotic interactions with rhizobial bacteria to form nitrogen-fixing nodules. Bacterial Nod factors (NFs) and plant regulatory pathways modulating NF signalling control rhizobial infections and nodulation efficiency. Here we show that gibberellin (GA) signalling mediated by DELLA proteins inhibits rhizobial infections and controls the NF induction of the infection marker ENOD11 in Medicago truncatula. Ectopic expression of a constitutively active DELLA protein in the epidermis is sufficient to promote ENOD11 expression in the absence of symbiotic signals. We show using heterologous systems that DELLA proteins can interact with the nodulation signalling pathway 2 (NSP2) and nuclear factor-YA1 (NF-YA1) transcription factors that are essential for the activation of NF responses. Furthermore, MtDELLA1 can bind the ERN1 (ERF required for nodulation 1) promoter and positively transactivate its expression. Overall, we propose that GA-dependent action of DELLA proteins may directly regulate the NSP1/NSP2 and NF-YA1 activation of ERN1 transcription to regulate rhizobial infections.

Highlights

Legumes develop symbiotic interactions with rhizobial bacteria to form nitrogen-fixing nodules
Nodulation signalling pathway 1 (NSP1) and 2 (NSP2), nuclear factor-YA1 (NF-YA1), ethylene response factor required for nodulation 1 (ERN1) and nodule inception proteins are involved in the transcriptional activation of the infection marker ENOD11 in the epidermis[8,9,10,11,12,13,14,15,16]
As we demonstrated that at least MtDELLA1 is required to induce ERN1 and ENOD11 expression in response to Nod factors (NFs) (Fig. 5c), and as DELLA proteins have been previously shown to interact with transcription factors[33], we tested if DELLA proteins were able to interact with the nodulation signalling pathway 1 (NSP1), nodulation signalling pathway 2 (NSP2) or NF-YA1 transcription factors (Fig. 6)

Summary

Introduction

Legumes develop symbiotic interactions with rhizobial bacteria to form nitrogen-fixing nodules. Calcium spiking is decoded by a calcium/calmodulin-dependent kinase named DMI3 (does not make infection 3) in M. truncatula, leading to the induction of nuclear transcriptional regulators essential to coordinate the expression of genes associated to rhizobial infection Among these transcription factors, nodulation signalling pathway 1 (NSP1) and 2 (NSP2), nuclear factor-YA1 (NF-YA1), ethylene response factor required for nodulation 1 (ERN1) and nodule inception proteins are involved in the transcriptional activation of the infection marker ENOD11 in the epidermis[8,9,10,11,12,13,14,15,16]. Depending on their ability to interact physically with different transcription factors, DELLA proteins were initially described as repressors of GA responses even though a function of the DELLA as transactivation factors was more recently proposed[33,37,38]

Methods

Results

Conclusion