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

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.

Advances and current challenges in calcium signaling

“…This decoding complex emerges as a dynamic signaling hub. The experimental support for the interaction between CC a MK and CIP 73 (Kang et al ., ), CC a MK and NAC 84 (Zhu et al ., ), CYCLOPS and DELLA (Jin et al ., ; Pimprikar et al ., ), DELLA and NSP 2 (Fonouni‐Farde et al ., ; Jin et al ., ), DELLA and NF ‐ YA 1 (Fonouni‐Farde et al ., ), DELLA and DIP 1 (Yu et al ., ), RAM 1 and NSP 2 (Gobbato et al ., ), and IPN 2 and NSP 2 (Kang et al ., ) differs significantly. Nevertheless, the overall accumulating evidence pinpoints the CC a MK / CYCLOPS complex as a hub recruiting a variety of interaction partners which probably mediate signaling specificity thus leading to the activation of distinct target genes.…”

“…The negative interference of GA signaling with nodulation and AM development recently could be mechanistically explained by the physical interaction between CYCLOPS with DELLA (Maekawa et al, 2009;Floss et al, 2013;Takeda et al, 2015;Fonouni-Farde et al, 2016;Jin et al, 2016;Pimprikar et al, 2016). DELLA is degraded upon GA binding and it is hypothetically possible that this recruitment of E3 ligases by DELLA leads to degradation of the entire CCaMK/CYLCOPS complex.…”

“…In the context of complex degradation, the interaction of CCaMK with a protein containing a scythe-N ubiquitin-like domain may deserve further investigation (Davi ere et al, 2008;Kang et al, 2011). Recently, the number of GRAS proteins involved in the regulation of symbiotic responses of the root has increased (Gobbato et al, 2012;Yu et al, 2014;Fonouni-Farde et al, 2016;Pimprikar et al, 2016). Because GRAS proteins have been shown to interact with DELLA which is itself a GRAS protein, it will be interesting to investigate which of these are, at least transiently, components of a larger CCaMK/CYCLOPS complex.…”

Hormone modulation of legume‐rhizobial symbiosis

“…Other reports showed that exogenous application of GA 3 inhibited NFs‐induced root hair deformation, infection thread formation and nodule development in L. japonicus and M. truncatula . Application of paclobutrazol (PAC), an inhibitor of GA biosynthesis, rescued this phenotype (Maekawa et al ; Fonouni‐Farde et al ; Jin et al ), which indicates negative regulation of GAs at infection thread formation and nodule development.…”

“…DELLAs functioned as a scaffold to bridge a protein complex containing IPD3 and NSP2 to promote nodulation (Jin et al ). Interestingly, DELLAs also interact with NF‐YA1, which is required for nodulation (Maekawa et al ; Fonouni‐Farde et al ; Jin et al ). This suggests that DELLA function through a large transcriptional complex to regulate expression of symbiotic genes in root nodule symbiosis.…”