Indole-3-Acetic Acid-Producing Yeasts in the Phyllosphere of the Carnivorous Plant Drosera indica L

Abstract

Yeasts are widely distributed in nature and exist in association with other microorganisms as normal inhabitants of soil, vegetation, and aqueous environments. In this study, 12 yeast strains were enriched and isolated from leaf samples of the carnivorous plant Drosera indica L., which is currently threatened because of restricted habitats and use in herbal industries. According to similarities in large subunit and small subunit ribosomal RNA gene sequences, we identified 2 yeast species in 2 genera of the phylum Ascomycota, and 5 yeast species in 5 genera of the phylum Basidiomycota. All of the isolated yeasts produced indole-3-acetic acid (IAA) when cultivated in YPD broth supplemented with 0.1% L-tryptophan. Growth conditions, such as the pH and temperature of the medium, influenced yeast IAA production. Our results also suggested the existence of a tryptophan-independent IAA biosynthetic pathway. We evaluated the effects of various concentrations of exogenous IAA on yeast growth and observed that IAA produced by wild yeasts modifies auxin-inducible gene expression in Arabidopsis. Our data suggest that yeasts can promote plant growth and support ongoing prospecting of yeast strains for inclusion into biofertilizer for sustainable agriculture.

Indole-3-acetic acid: A widespread physiological code in interactions of fungi with other organisms

“…In addition, our previous study supports that IAA production is influenced by the pH value of the medium. 26 We observed that 6 of 12 tested yeast isolates produced low levels of IAA, 5 isolates produced similar levels of IAA, and one isolate produced high levels of IAA in an acidic environment than in a nearly neutral environment. All of the isolates could not produce IAA in an alkaline environment (pH 9).…”

“…26 The tested yeast strains were collected from leaf samples of the carnivorous plant Drosera indica L. We found that the growth of Ustilago esculenta was not influenced by any tested IAA concentration and that a high IAA concentration (5,000 mM) significantly inhibited the growth of 11 of 12 plant-associated yeasts. In the phylum Ascomycota, low concentrations of exogenous IAA (312.5-625 mM) promoted or did not influence yeast growth.…”

“…17 To confirm the presence of a Trpindependent pathway in yeasts, we analyzed IAA production in yeast cultures without Trp. 26 We observed that 11 of 12 tested yeast isolates produced IAA in the absence of exogenous Trp. Five isolates produced high levels of IAA, and 5 isolates produced low levels of IAA.…”

“…24 Gas chromatography analysis of the Fusarium delphinoides strain GPK culture filtrates has shown the presence of metabolic intermediates of IPA, IAM, and TRA pathways. 25 In our recent study, 26 all of the isolated yeasts produced IAA in yeast extract-peptone-dextrose (YPD) broth supplemented with 0.1% L-Trp. Limtong and Koowadjanakul 9 collected yeasts from the phyllosphere of various plant species in Thailand and observed that approximately 37.7% of the investigated yeast strains produced IAA.…”

“…51 Fungal-produced IAA can induce lateral root formation and root hair development. 26 The promotion of root growth and development causes enhanced nutrient absorption by the associated plants. Consecutively, the shoot and/or fruit biomass production increases.…”