Pseudomonas fluorescens and Trichoderma asperellum Enhance Expression of Gα Subunits of the Pea Heterotrimeric G-protein during Erysiphe pisi Infection

Abstract

We investigated the transcript accumulation patterns of all three subunits of heterotrimeric G-proteins (Gα1 and 2, Gβ, and Gγ) in pea under stimulation of two soil-inhabiting rhizosphere microbes Pseudomonas fluorescens OKC and Trichoderma asperellum T42. The microbes were either applied individually or co-inoculated and the transcript accumulation patterns were also investigated after challenging the same plants with a fungal biotrophic pathogen Erysiphe pisi. We observed that mostly the transcripts of Gα 1 and 2 subunits were accumulated when the plants were treated with the microbes (OKC and T42) either individually or co-inoculated. However, transcript accumulations of Gα subunits were highest in the T42 treatment particularly under the challenge of the biotroph. Transcript accumulations of the other two subunits Gβ and Gγ were either basal or even lower than the basal level. There was an indication for involvement of JA-mediated pathway in the same situations as activation of LOX1 and COI1 were relatively enhanced in the microbe co-inoculated treatments. Non-increment of SA content as well as transcripts of SA-dependent PR1 suggested non-activation of the SA-mediated signal transduction in the interaction of pea with E. pisi under the stimuli of OKC and T42. Gα1 and 2 transcript accumulations were further correlated with peroxidases activities, H2O2 generation and accumulation in ABA in pea leaves under OKC and T42 stimulations and all these activities were positively correlated with stomata closure at early stage of the biotroph challenge. The microbe-induced physiological responses in pea leaves finally led to reduced E. pisi development particularly in OKC and T42 co-inoculated plants. We conclude that OKC and T42 pretreatment stimulate transcript accumulations of the Gα1 and Gα2 subunits of the heterotrimeric G protein, peroxidases activities and phenol accumulation in pea during infection by E. pisi. The signal transduction was possibly mediated through JA in pea under the stimulus of the microbes and the cumulative effect of the co-inoculated microbes had a suppressive effect on E. pisi conidial development on pea leaves.

Trichoderma asperellumT42 induces local defense againstXanthomonas oryzaepv.oryzaeunder nitrate and ammonium nutrients in tobacco

“…A similar view was also reported in maize, where H 2 O 2 production was generated in the early stage of infection of a fungal hypha of Colletotrichum graminicola. 20,49 Moreover, H 2 O 2 production was also observed in Arabidopsis aer colonization with T. virens 43 and in pea by Trichoderma asperellum. 20 The higher accumulation of H 2 O 2 production in the Trichoderma-inoculated plants grown in N nutrients provides evidence that Trichoderma can promote H 2 O 2 production under N nutrients during Xoo infection.…”

“…Moreover, Trichoderma may induce multiple secondary metabolites, auxin production and phenolic compounds, which may enhance the defense mechanisms in plants. [19][20][21] Therefore, systems that can enhance the affinity for N uptake and promote disease resistance in plants are necessary. Several plant symbiotic microbes are well known as plant growth promoters, which facilitate nutrient availability to plants.…”

“…6,12 Perhaps, the activation of these defense responses is due to the modulation of metabolites and defense genes involved in the resistance mechanism. 20,23 If Trichoderma initiates an enhanced N uptake efficiency 6 and NO accumulation, 12 it may be implicated in plant defense via HR-mediated cell death. Trichoderma asperellum T42 as a biological control agent and Xanthomonas oryzae pv.…”

Potential modes of action of Pseudomonas fluorescens ZX during biocontrol of blue mold decay on postharvest citrus

“…As an effective biocontrol agent, P. fluorescens has been studied extensively for its use in preventing plant disease of the rhizosphere. At present, it is generally believed that the main antagonistic mechanisms of P. fluorescens during control of plant pathogens include parasitism, competition for nutrients and space, production of secondary resistance metabolites and initiation of systemic resistance . Many studies have shown that the mechanisms of action of biocontrol agents are influenced by many factors, such as the fungal pathogen, plant host and storage environment, and are not associated with only a single mode of action .…”

“…At present, it is generally believed that the main antagonistic mechanisms of P. fluorescens during control of plant pathogens include parasitism, 20,21 competition for nutrients and space, 12,[20][21][22] production of secondary resistance metabolites [23][24][25] and initiation of systemic resistance. [25][26][27] Many studies have shown that the mechanisms of action of biocontrol agents are influenced by many factors, such as the fungal pathogen, plant host and storage environment, and are not associated with only a single mode of action. 12,21 To the best of our knowledge, little is known about P. fluorescens biocontrol of postharvest disease of citrus fruits, and understanding the associated mechanisms of antagonism is important for improving biocontrol efficacy and expanding the microbial applications in controlling postharvest diseases.…”