Putative Role of a Yet Uncharacterized Protein Elicitor PeBb1 Derived from Beauveria bassiana ARSEF 2860 Strain against Myzus persicae (Homoptera: Aphididae) in Brassica rapa ssp. pekinensis

Transcriptome analysis of Beauveria bassiana interaction with Nicotiana benthamiana reveals signatures of N. Benthamiana growth promotion and enhanced defense responses

Many entomopathogenic fungi form intimate (epi- and endo-phytic) associations with that plant that can stimulate plant growth and /or improve resistance to pathogens and insect pests. However, little is known concerning global gene networks that mediate such responses. Nicotiana benthamiana seedlings were artificially colonized by the entomogenous fungus, Beauveria bassiana, and the root tissues were examined via comparative transcriptome analyses performed versus fungal cells grown in vitro on dried root biomass. Plant hormone pathways, and genes involved in photosynthesis, immune defense response, and nutrient metabolism were triggered in roots after fungal colonization. Fungal differentially expressed genes during plant colonization included plant cell wall-degrading enzymes, and those involved in lipid metabolism, detoxification, and fungal cell wall remodeling, the latter suggesting reduction in the exposure of pathogen related molecular patterns to avoid perception by the plant immune system. Fungal metabolic genes involved in amino acid, nitrogen, sulfur and carbohydrate assimilation were activated, nutrient exchange with the plant host. Exchange was confirmed by detection of sulfur in the seedling that was increased by the fungal colonization. A set of fungal secondary metabolism-associated genes were also upregulated during the plant interaction, which might contribute to plant resistance against pathogens or/and insect pest. In addition, B. bassiana expressed a suite of effector/elicitor genes consistent with triggering plant growth and/or immune defense response pathways. These results revealed global gene networks active in both the plants and the fungus as a consequence of their symbiotic interaction, and provides insights into the molecular determinants and physiological responses affected.

The Conserved Cysteine-Rich Secretory Protein MaCFEM85 Interacts with MsWAK16 to Activate Plant Defenses

Metarhizium anisopliae is an entomopathogenic fungus which may enhance plant growth and resistance when acting as an endophyte in host plants. However, little is known about the protein interactions nor their activating mechanisms. Common in fungal extracellular membrane (CFEM) proteins have been identified as plant immune regulators that suppress or activate plant resistance responses. Here, we identified a CFEM domain-containing protein, MaCFEM85, which was mainly localized in the plasma membrane. Yeast two-hybrid (Y2H), glutathione-S-transferase (GST) pull-down, and bimolecular fluorescence complementation assays demonstrated that MaCFEM85 interacted with the extracellular domain of a Medicago sativa (alfalfa) membrane protein, MsWAK16. Gene expression analyses showed that MaCFEM85 and MsWAK16 were significantly upregulated in M. anisopliae and M. sativa, respectively, from 12 to 60 h after co-inoculation. Additional yeast two-hybrid assays and amino acid site-specific mutation indicated that the CFEM domain and 52th cysteine specifically were required for the interaction of MaCFEM85 with MsWAK16. Defense function assays showed that JA was up-regulated, but Botrytis cinerea lesion size and Myzus persicae reproduction were suppressed by transient expression of MaCFEM85 and MsWAK16 in the model host plant Nicotiana benthamiana. Collectively, these results provide novel insights into the molecular mechanisms underlying interactions of M. anisopliae with host plants.

A Novel Protein Elicitor (PELL1) Extracted from Lecanicillium lecanii Induced Resistance against Bemisia tabaci (Hemiptera: Aleyrodidae) in Gossypium hirsutum L

Protein elicitors play a key role in signaling or displaying plant defense mechanism and emerging as vital tools for biocontrol of insects. This study was aimed at the characterization of the novel protein elicitor isolated from entomopathogenic fungi Lecanicillium lecanii (V3) strain and its activity against whitefly, Bemisia tabaci, in cotton (Gossypium hirsutum L.). The sequence of purified elicitor protein showed 100% similarity with hypothetical protein LEL_00878 (Cordyceps confragosa RCEF 1005) (GenBank accession no. OAA81333.1). This novel protein elicitor has 253 amino acid residues and 762 bp with a molecular mass of 29 kDa. Their combatant protein was expressed in Escherichia coli using pET-28a (+) plasmid. Bioassay was revealed to quantify the impact of numerous concentrations of protein (i.e., 58.32, 41.22, and 35.41 μg/ml) on the fecundity rate of B tabaci on cotton plants. Bioassay results exhibited a significant effect (P ≤ 0.001) of all the concentrations of protein on the fecundity rate of B. tabaci. In addition, the gene expression analysis found a significant upregulation of the major genes associated with salicylic acid (SA) and jasmonic acid (JA) defense pathways in elicitor protein-treated plants. Our results showed that the potential application of novel protein elicitor derived from Lecanicillium lecanii will be used as future biointensive controlling approaches against whitefly, Bemisia tabaci.

Pest management via endophytic colonization of tobacco seedlings by the insect fungal pathogen Beauveria bassiana

BACKGROUND

It has been suggested that entomopathogenic fungi can be introduced into plants as endophytes potentially leading to insect control. Here, we sought to identify specific strains of the insect pathogenic fungus, Beauveria bassiana that would form endophytic associations with tobacco (Nicotiana benthamiana) benefitting host plant growth and/or resistance against insect pests and pathogens.

RESULTS

Tobacco seeds were inoculated with six different B. bassiana strains and entophytic colonization, plant growth, and resistance to pathogens and insect pests were evaluated over a 50 day-period. Although all the strains could colonize seedlings, 90% seedling colonization was seen for four strains. Fungal cells could be detected in stems more readily than in leaf and root tissues. Colonization by B. bassiana boosted plant growth with an increased photosynthetic rate, chlorophyll content, and stomatal and trichome density seen in fungal treated plants. Tobacco seedlings colonized by specific B. bassiana strains displayed significantly increased tolerance/resistance against bacterial and fungal pathogens. B. bassiana-colonized seedlings also displayed higher resistance to aphids (Myzus persicae) as compared to untreated controls. Colonization by B. bassiana was shown to trigger both of the salicylic acid (SA) and jasmonate acid (JA) defense pathways, but SA pathway was upregulated much more than JA pathway for some of the tested strains.

CONCLUSION

Specific strains of B. bassiana can be introduced into host plants as endophytes, resulting in promotion of host plant growth, increased resistance to microbial pathogens, and/or increased resistance to insect pests. © 2020 Society of Chemical Industry.

Sub-Lethal Effects of Partially Purified Protein Extracted from Beauveria bassiana (Balsamo) and Its Presumptive Role in Tomato (Lycopersicon esculentum L.) Defense against Whitefly (Bemisia tabaci Genn.)

Simple Summary

Apart from their direct entomopathogenicity, many entomopathogenic fungi synthesize protein molecules that can trigger plant defense mechanisms against herbivore insect pests. This laboratory study determined the sub-lethal effects of a partially purified protein derived from Beauveria bassiana against whitefly Bemisia tabaci on tomato plants along with the subsequent gene expression analyses of key gens potentially linked to jasmonic acid (JA) and salicylic acid (SA) associated plant defense pathways. The exogenous foliar application of B. bassiana-derived protein significantly reduced the whitefly survival and fecundity parameters concomitantly with an up-regulation of all the plant defense associated genes, particularly of SA pathway genes. These findings demonstrate the putative role of this partially purified entomopathogenic fungal protein and suggest its further purification and characterization for using in future microbial pest control strategies against whiteflies and other sap-feeding insect pests.

Abstract

Plants rely on various physiological and molecular defense mechanisms against biotic stresses such as herbivore insects. Many entomopathogenic fungi synthesize protein molecules that can trigger these plant defenses. This laboratory study characterized the bioactivity of a partially purified protein derived from Beauveria bassiana (ARSEF 2860) against whitefly, Bemisia tabaci (Hemiptera: Aleyrodidae), which is an economically important pest of agricultural and horticultural crops worldwide. Different concentrations (i.e., 0.021, 0.042 and 0.063 μM) of fungal protein were bioassayed to determine their sub-lethal effect on the survival percentage and fecundity rate of B. tabaci on tomato (Lycopersicon esculentum) plants. In addition, the putative role of this partially purified B. bassiana protein in the defense mechanisms of plant was assessed through the expression analyses of important genes related to salicylic acid (SA)—and jasmonic acid (JA)—associated pathways using RT-qPCR. Results revealed a significant suppression of the survival percentage and fecundity rate of B. tabaci by the fungal protein. Lowest survival (41%) was recorded for the highest concentration of protein (0.063 μM), whereas mean survival for the other two protein concentrations (0.042 and 0.021 μM) were 62 and 71%, respectively. Likewise, the highest and lowest mean fecundity rates were observed for the control and the highest protein concentration (i.e., 3.3 and 1.8 eggs day⁻¹ female⁻¹, respectively). Furthermore, the exogenous application of B. bassiana-derived protein on tomato plants strongly up-regulated the SA-related genes (PAL, PR1, BGL2 and EDS1) and slightly up-regulated the JA-related genes (AOC, AOS, OPR3 and LOX) as compared to the control plants. These findings demonstrate the putative role of this partially purified B. bassiana protein fraction in inducing systemic resistance in the tomato plants against B. tabaci, suggesting its further purification and characterization to be used as novel biological pest control tool against B. tabaci and other sap-sucking insect pests.