AUTHOR=Labbé Jessy L. , Weston David J. , Dunkirk Nora , Pelletier Dale A. , Tuskan Gerald A. 

TITLE=Newly identified helper bacteria stimulate ectomycorrhizal formation in Populus

JOURNAL=Frontiers in Plant Science

VOLUME=5

YEAR=2014

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2014.00579

DOI=10.3389/fpls.2014.00579

ISSN=1664-462X

ABSTRACT=<p>Mycorrhiza helper bacteria (MHB) are known to increase host root colonization by mycorrhizal fungi but the molecular mechanisms and potential tripartite interactions are poorly understood. Through an effort to study <italic>Populus</italic> microbiome, we isolated 21 <italic>Pseudomonas</italic> strains from native <italic>Populus deltoides</italic> roots. These bacterial isolates were characterized and screened for MHB effectiveness on the <italic>Populus-Laccaria</italic> system. Two additional <italic>Pseudomonas</italic> strains (i.e., Pf-5 and BBc6R8) from existing collections were included for comparative purposes. We analyzed the effect of co-cultivation of these 23 individual <italic>Pseudomonas</italic> strains on <italic>Laccaria bicolor</italic> “S238N” growth rate, mycelial architecture and transcriptional changes. Nineteen of the 23 <italic>Pseudomonas</italic> strains tested had positive effects on <italic>L. bicolor</italic> S238N growth, as well as on mycelial architecture, with strains GM41 and GM18 having the most significant effect. Four of seven <italic>L. bicolor</italic> reporter genes, <italic>Tra1, Tectonin2, Gcn5</italic>, and <italic>Cipc1</italic>, thought to be regulated during the interaction with MHB strain BBc6R8, were induced or repressed, while interacting with <italic>Pseudomonas</italic> strains GM17, GM33, GM41, GM48, Pf-5, and BBc6R8. Strain GM41 promoted the highest roots colonization across three <italic>Populus</italic> species but most notably in <italic>P. deltoides</italic>, which is otherwise poorly colonized by <italic>L. bicolor</italic>. Here we report novel MHB strains isolated from native <italic>Populus</italic> that improve <italic>L. bicolor</italic> root colonization on <italic>Populus</italic>. This tripartite relationship could be exploited for <italic>Populus</italic> species/genotypes nursery production as a means of improving establishment and survival in marginal lands.</p>