Small Proteins Secreted by Poplar Roots Form Communication Route with Associated Fungal Communities

The Science

Small proteins that are secreted from the plant roots were found to act as communication signals between the plant and associated beneficial fungus. These molecular cues have the potential to alter development of both beneficial and pathogenic fungi.

The Impact

This work elucidates the complex communications that occur between mutualistic plant-microbe interactions and the influence of such associations on both partners, opening new avenues for development of high-yielding, sustainable bioenergy field crops.


Microbial communities surrounding plant roots can form symbiotic associations with the plant, an interaction that requires complex communications between both organisms. Mutualistic associations offer several benefits to the plant such as enhanced growth and tolerance to drought. Mutualistic fungi have evolved elaborate protein-based signals (effectors) that communicate their metabolic requirements to their plant hosts; in turn, root exudates contain small secreted proteins (SSPs) that influence mutualism with the microbes and could function as effector proteins during symbiotic interactions. While many new SSPs have been discovered through annotation of plant genome sequences, their roles as secreted effector proteins during mutualistic symbiosis was uncertain. Researchers at the Oak Ridge National Laboratory, supported by the DOE BER Plant-Microbe Interfaces Scientific Focus Area, used computational prediction and experimentation to identify SSPs in the bioenergy tree Populus trichocarpa and elucidate their effect during mutualistic symbiosis with the ectomycorrhizal fungus, Laccaria bicolor. Of the 2,819 Populus protein-encoding genes that were identified as differentially expressed across all stages of mycorrhizal root tip development during symbiosis between P. trichocarpa and L. bicolor, 417 were predicted to be SSPs (=250 aa in length). Experimentation verified that a subset of these SSPs were able to enter and accumulate in L. bicolor, then alter the development of multiple ectomycorrhizal and pathogenic fungi. This study demonstrates that SSPs in Populus can function as effector proteins during symbiotic interactions, highlighting a novel avenue by which plants communicate with and possibly influence their mutualistic microbial partners.

Principal Investigator(s)

Xiaohan Yang
Biosciences Division, Oak Ridge National Laboratory


Genomic Science Program, US Department of Energy, Office of Science, Biological and Environmental Research, as part of the Plant-Microbe Interfaces Scientific Focus Area (http://pmi. ornl.gov).


J.M. Plett, H. Yin, R. Mewalal, R. Hu, T. Li, P. Ranjan, S. Jawdy, H.C. DePaoli, G. Butler, T.M. Burch-Smith, H-B Guo, C.J. Chen, A Kohler, I.C. Anderson, J.L. Labbé, F. Martin, G.A. Tuskan, and X. Yang, “Populus trichocarpa encodes small, effector-like secreted proteins that are highly induced during mutualistic symbiosis.” Scientific Reports 7:382 (2017). [DOI:10.1038/s41598-017-00400-8].