DELLA proteins are common components of symbiotic rhizobial and mycorrhizal signalling pathways

Abstract

Legumes form symbiotic associations with either nitrogen-fixing bacteria or arbuscular mycorrhizal fungi. Formation of these two symbioses is regulated by a common set of signalling components that act downstream of recognition of rhizobia or mycorrhizae by host plants. Central to these pathways is the calcium and calmodulin-dependent protein kinase (CCaMK)–IPD3 complex which initiates nodule organogenesis following calcium oscillations in the host nucleus. However, downstream signalling events are not fully understood. Here we show that Medicago truncatula DELLA proteins, which are the central regulators of gibberellic acid signalling, positively regulate rhizobial symbiosis. Rhizobia colonization is impaired in della mutants and we provide evidence that DELLAs can promote CCaMK–IPD3 complex formation and increase the phosphorylation state of IPD3. DELLAs can also interact with NSP2–NSP1 and enhance the expression of Nod-factor-inducible genes in protoplasts. We show that DELLA is able to bridge a protein complex containing IPD3 and NSP2. Our results suggest a transcriptional framework for regulation of root nodule symbiosis.

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.…”

“…Recently, we showed that DELLA proteins, the central negative regulators of the GA signaling pathway, act as a common component of rhizobial symbiosis and mycorrhizal symbiosis (Jin et al ). Triple Mtdella mutants exhibited a strong impairment in infection thread formation and nodule development and induced most NFs‐inducible genes (Jin et al ).…”

“…Recently, we showed that DELLA proteins, the central negative regulators of the GA signaling pathway, act as a common component of rhizobial symbiosis and mycorrhizal symbiosis (Jin et al ). Triple Mtdella mutants exhibited a strong impairment in infection thread formation and nodule development and induced most NFs‐inducible genes (Jin et al ). Biochemical analysis showed MtDELLAs could not only promote CCaMK–IPD3 complex formation, to increase phosphorylation of IPD3, but also could interact with the NSP2–NSP1 complex to enhance expression of NFs‐inducible genes.…”

“…Biochemical analysis showed MtDELLAs could not only promote CCaMK–IPD3 complex formation, to increase phosphorylation of IPD3, but also could interact with the NSP2–NSP1 complex to enhance expression of NFs‐inducible genes. 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 ).…”

Presidential address: recent advance of mycorrhizal research in China

“…Moreover, Chinese scientists have made significant progress in terms of mycorrhizal signal transduction, for example, some specific proteins such as DELLA and CERK1, were found to be common components of symbiotic mycorrhizal signalling pathways and to play critical function during the establishment of symbiosis between AM fungi and host plants (e.g. Yu et al 2014; Zhang et al 2015; Jin et al 2016). …”