Fusarium Oxysporum Volatiles Enhance Plant Growth Via Affecting Auxin Transport and Signaling

Abstract

Volatile organic compounds (VOCs) have well-documented roles in plant-plant communication and directing animal behavior. In this study, we examine the less understood roles of VOCs in plant-fungal relationships. Phylogenetically and ecologically diverse strains of Fusarium oxysporum, a fungal species complex that often resides in the rhizosphere of assorted plants, produce volatile compounds that augment shoot and root growth of Arabidopsis thaliana and tobacco. Growth responses of A. thaliana hormone signaling mutants and expression patterns of a GUS reporter gene under the auxin-responsive DR5 promoter supported the involvement of auxin signaling in F. oxysporum volatile-mediated growth enhancement. In addition, 1-naphthylthalamic acid, an inhibitor of auxin efflux, negated F. oxysporum volatile-mediated growth enhancement in both plants. Comparison of the profiles of volatile compounds produced by F. oxysporum strains that differentially affected plant growth suggests that the relative compositions of both growth inhibitory and stimulatory compounds may determine the degree of plant growth enhancement. Volatile-mediated signaling between fungi and plants may represent a potentially conserved, yet mostly overlooked, mechanism underpinning plant-fungus interactions and fungal niche adaption.

Do volatile compounds produced by Fusarium oxysporum and Verticillium dahliae affect stress tolerance in plants?

“…Bi-partite Petri plate (=I plate), which has been widely used for studying VC-mediated interaction between fungi and plants (Zhang et al 2008; Paul and Park 2013; Bitas et al 2015), was employed for this assessment. One compartment of I plate contained 12 ml half-strength PDA for culturing fungus, and the other compartment had 12 ml Murashige and Skoog (MS) medium (Sigma-Aldrich, St. Louis, MO) supplemented with no NaCl or 100 mM NaCl.…”

“…One compartment of I plate contained 12 ml half-strength PDA for culturing fungus, and the other compartment had 12 ml Murashige and Skoog (MS) medium (Sigma-Aldrich, St. Louis, MO) supplemented with no NaCl or 100 mM NaCl. Seed treatment was conducted as described in Bitas et al (2015). Arabidopsis is a glycophytic plant and is sensitive to high salt throughout its development stages, especially during seed germination and seedling (Xiong and Zhu 2002), Accordingly, prior to exposing A. thaliana seedlings to 100 mM NaCl, they were germinated and grown on MS medium supplemented with 0.8% (w/v) agar and 0.25% (w/v) sucrose for 7 days.…”

“…Arabidopsis is a glycophytic plant and is sensitive to high salt throughout its development stages, especially during seed germination and seedling (Xiong and Zhu 2002), Accordingly, prior to exposing A. thaliana seedlings to 100 mM NaCl, they were germinated and grown on MS medium supplemented with 0.8% (w/v) agar and 0.25% (w/v) sucrose for 7 days. One plug of fungal culture (5 mm in diameter) was inoculated on the PDA side, and five Col-0 seedlings were transplanted to the MS side to initiate co-cultivation (Bitas et al 2015). The control treatment for all experiments consisted of PDA alone (no fungus).…”

“…Histochemical staining to assess GUS activity in three transgenic A. thaliana lines that contain DR5::GUS, PR1::GUS and PDF1.2::GUS , respectively, was performed as previously described (Bitas et al 2015). Vacuum was applied for 5 min to seedlings in 50 mM sodium phosphate (pH 7.0), 0.1% (v/v) Triton X-100, 2 mM K 4 Fe(CN) 6 , 2 mM K 3 Fe(CN) 6 and 2 mM X-Gluc (5-bromo-4-chloro-3-indolyl-beta- d -glucuronic acid, cyclohexylammonium salt, Gold Biotechnology, Olivette, MO).…”

“…VCs produced by both fungi have been shown to affect plant growth and development, and the underlying mechanism involves components of auxin signalling (Bitas et al 2015; Li et al 2018). However, how their VCs affect plant responses to (a)biotic stresses has not been studied.…”