Plant-Microbe interactions and nutrient acquistion

Improving the efficiency of plant nutrient acquisition is important for the development of more closed nutrient cycles in plant production systems. We focus on contributions from members of the soil microbiome that increase nutrient acquisition, either directly by the formation of symbiotic root-microbe associations or indirectly by their effects on root growth patterns.

Mycorrhiza to improve phosphorus uptake
Our research has shown that phosphorus (P) uptake via arbuscular mycorrhiza (AM) fungi may dominate total P uptake, even in plants that do not grow better when colonized by AM fungi (Smith et al 2011). While the P transfer from fungus to plant is efficiently mediated by AM-induced Pi transporters in the peri-arbuscular membrane (Yang et al 2012), the overall P uptake by AM plants strongly depends on the abundance of root-external AM mycelium in the soil (Jakobsen et al 2016; Sawers et al 2016). We aim to enhance P uptake via the AM pathway by optimizing the proliferation of the AM mycelium into soil regions outside the root P depletion zone. This will require a solid understanding of interactions with other components of the soil microbiome as well as mechanistic insight into plant signaling pathways that control the symbiotic relationships.

Small signaling peptides (SSPs) controlling nodulation and root development
A group of soil bacteria, collectively called rhizobia, induce the formation of root nodules in legume plants. In the nodules, rhizobia fix atmospheric nitrogen (N) and make it available to the plant. As a result, legumes are independent of N fertilization and thus represent an integral part of sustainable agricultural systems. Small signaling peptides (SSPs) constitute a new class of important regulators of plant growth and development. We are currently identifying SSPs in the legume model plants Medicago truncatula and Lotus japonicus (Hastwell et al. 2016), and are exploring their roles in nodulation, root development and mycorrhizal symbiosis (de Bang et al. unpublished). We want to understand how legume SSPs control and regulate these symbiotic interactions, and aim to apply this knowledge to improve nutrient uptake under field conditions.

Current research activities in 2016/17

Soil-related suppression of root-external AM mycelium 
We have generated evidence that unidentified factors suppress the growth of the AM mycelium and that the suppression varies markedly between soils. We test the hypotheses that (1) specific groups of microorganisms are associated with soil suppression of AM mycelium, (2) specific microbial metabolites are responsible for the suppression and (3) it is possible to diagnose and counteract the suppression on a field scale. Researchers: Iver Jakobsen, Carla Cruz Paredes, Ole Nybroe, Jan H Christensen. Contact ivja@plen.ku.dk

Phosphate transfer at the fungus-plant interface in AM-colonised Medicago truncatula
The peri-arbuscular membrane in M. truncatula contains at least two Pi transporters. Various Pi transporter mutants obtained from Maria Harrison, Boyce Thompson Institute, Ithaca, USA are used in experiments with radioactive tracers to determine the function of each transporter in P uptake via the AM pathway Researchers: Iver Jakobsen. Contact ivja@plen.ku.dk

Phosphate-solubilizing Penicillium and AM fungi
The aim is to determine the ability of Penicillium to improve the P uptake from gasification ashes in wheat and to identify the mechanisms involved. We also test the hypothesis that AM fungi will capture the Penicillium-solubilized ash-P and thereby promote its plant availability. Researchers: Aikaterini Efthymiou, Iver Jakobsen. Contact: ivja@plen.ku.dk

Peptides regulating mycorrhizal symbiosis
Transcriptomic studies have identified small signaling peptides (SSPs) with differential expression patterns during mycorrhizal symbiosis and phosphate availability. The aim of this project is to identity SSPs important for regulating the symbiotic interaction with mycorrhiza and to elucidate the underlying signaling pathways.Researchers: Iver Jakobsen, Thomas C de Bang. Contact tdb@plen.ku.dk

Nitrogen-dependent root development controlled by receptor kinases
Small signaling peptides transmit their signals through leucine-rich receptor-like kinases (LRR-RLKs). We are investigating the role of a specific LRR-RLK in nitrogen-dependent root development. The project is carried out with partners from Institute of Plant Science and Université Paris-Saclay, France and from the Samuel Roberts Noble Foundation, USA. Contact: tdb@plen.ku.dk.

Characterization of nodule-specific SSPs and their role in nitrogen fixation
Genome-wide identification SSPs in the legume model species Medicago truncatula, combined with large-scale RNA-seq based expression analyses, revealed that multiple SSPs were involved in the nodulation process. In this project, the aim is to elucidate the function of selected nodule-specific SSPs in relation to nodule development and nitrogen fixation.The project is carried out in collaboration with partners from the Samuel Roberts Noble Foundation, USA. Researchers: Anders Peter Wätjen (MSc student) Thomas C de Bang. Contact: tdb@plen.ku.dk




Publications:
 

  • Jakobsen I, Smith SE, Smith FA, Watts-Williams SJ, Clausen SS, Grønlund M. 2016. Plant growth responses to elevated atmospheric CO2 are increased by phosphorus sufficiency but not by arbuscular mycorrhizas. Journal of Experimental Botany, 67: 6173-6186
  • Sawers RJH, Svane SF, Quan C, Grønlund M, Wozniak B , González-Muñoz E , Montes RAC , Baxter I, Goudet J, Jakobsen I, Paszkowski U. Phosphorus acquisition efficiency in arbuscular mycorrhizal maize is correlated with the abundance of root-external hyphae and the accumulation of transcripts encoding PHT1 phosphate transporters. New Phytologist (accepted)
  • Yang S-Y, Grønlund M, Jakobsen I, Grotemeyer MS, Rentsch D, Miyao A, Hirochika H, Kumar CS, Sundaresan V,Salamin N, Catausan S, Mattes N, Heuer S and Paszkowski U. 2012. Nonredundant Regulation of Rice Arbuscular Mycorrhizal Symbiosis by Two Members of the Phosphate Transporter 1 Gene Family - Plant Cell 24: 4236-4251
  • Smith SE, Jakobsen I, Grønlund M and Smith FA. 2011. Roles of arbuscular mycorrhizas in plant phosphorus (P) nutrition: interactions between pathways of P uptake in arbuscular mycorrhizal (AM) roots have important implications for understanding and manipulating plant P acquisition – Plant Physiology 156: 1050-1057
  • Hastwell AH, de Bang TC, Gresshoff PM and Ferguson BJ.  CLAVATA3/ESR (CLE) peptide-encoding gene families identified in the model legumes, Medicago truncatula and Lotus japonicus, compared with those of Glycine max, Phaseolus vulgaris and Arabidopsis thaliana. (Ready for submission).
  • de Bang TC, Lundquist PK, Roy S, Dai X, Udvardi MK, Zhao P and Scheible WR. Genome-wide identification of small signaling peptides in Medicago truncatula (In preparation).