Invisible Signals from the Underground: Bacterial Volatiles Elicit Plant GrowthPromotion and Induce Systemic Resistance

Ryu, Choong Min; Farag, Mohammed A.; Pare, Paul. W.; Kloepper, Joseph W.

The Plant Pathology Journal 2005;21(1):7-12.
Published online March 31, 2005.

Invisible Signals from the Underground: Bacterial Volatiles Elicit Plant GrowthPromotion and Induce Systemic Resistance

Choong Min Ryu, Mohammed A. Farag, Paul. W. Pare, Joseph W. Kloepper

Abstract

Plant growth-promoting rhizobacteria (PGPR) are a wide range of root-colonizing bacteria with the capacity to enhance plant growth and control plant pathogens.Here we review recent progress that indicate some PGPR strains release a blend of volatile organic compounds (VOCs) that promote growth in Arabidopsis seedlings and induce resistance against Erwinia carotovora subsp. carotovora. In particular, the volatile components 2,3-butanediol and acetoin released exclusively from the PGPR strains triggered the greatest level of growth promotion and induced systemic resistance. Pharmacological applications of 2,3-butanediol promoted the plant growth and induced resistance,while bacterial mutants blocked in 2,3-butanediol and acetoin synthesis was devoid of growth-promotion and induced resistance capacities. The results suggested that the bacterial VOCs play a critical role in the plant growth promotion and induced resistance by PGPR. Using transgenic and mutant lines of Arabidopsis, we provide evidences that the signal pathway activated by volatiles from one PGPR strain is dependent on cytokinin activation for growth promotion and dependent on an ethylene-signaling pathway for induced pathogen resistance. This discovery provides new insight into the role of bacterial VOCs as initiators of both plant growth promotion and defense responses in plants.

Key Words: bacterial volatiles, induced systemic resistance, PGPR, volatile organic compounds