AUTHOR=Martínez-Hidalgo Pilar , García Juan M. , Pozo María J. 

TITLE=Induced systemic resistance against Botrytis cinerea by Micromonospora strains isolated from root nodules

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00922

DOI=10.3389/fmicb.2015.00922

ISSN=1664-302X

ABSTRACT=<p><italic>Micromonospora</italic> is a Gram positive bacterium that can be isolated from nitrogen fixing nodules from healthy leguminous plants, where they could be beneficial to the plant. Their plant growth promoting activity in legume and non-legume plants has been previously demonstrated. The present study explores the ability of <italic>Micromonospora</italic> strains to control fungal pathogens and to stimulate plant immunity. <italic>Micromonospora</italic> strains isolated from surface sterilized nodules of alfalfa showed <italic>in vitro</italic> antifungal activity against several pathogenic fungi. Moreover, root inoculation of tomato plants with these <italic>Micromonospora</italic> strains effectively reduced leaf infection by the fungal pathogen <italic>Botrytis cinerea</italic>, despite spatial separation between both microorganisms. This induced systemic resistance, confirmed in different tomato cultivars, is long lasting. Gene expression analyses evidenced that <italic>Micromonospora</italic> stimulates the plant capacity to activate defense mechanisms upon pathogen attack. The defensive response of tomato plants inoculated with <italic>Micromonospora</italic> spp. differs from that of non-inoculated plants, showing a stronger induction of jasmonate-regulated defenses when the plant is challenged with a pathogen. The hypothesis of jasmonates playing a key role in this defense priming effect was confirmed using defense-impaired tomato mutants, since the JA-deficient line <italic>def1</italic> was unable to display a long term induced resistance upon <italic>Micromonospora</italic> spp. inoculation. In conclusion, nodule isolated <italic>Micromonospora</italic> strains should be considered excellent candidates as biocontrol agents as they combine both direct antifungal activity against plant pathogens and the ability to prime plant immunity.</p>