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.
Highlights
Plants are populated by microorganisms below and above ground
The D1/D2 domain of the large subunit (LSU) and small subunit (SSU) ribosomal RNA (rRNA) gene sequences indicated that we isolated 12 yeast strains in the phyllosphere of D. indica
Our results strongly support the existence of a Trp-independent indole-3acetic acid (IAA) biosynthetic pathway in yeast and suggest the potential use of IAA-producing yeasts as biofertilizer inoculants to promote plant growth
Summary
Plants are populated by microorganisms below and above ground. Above-ground plant parts are typically colonized by microorganisms, such as different genera of bacteria, filamentous fungi, yeasts, algae, and, less frequently, protozoa and PLOS ONE | DOI:10.1371/journal.pone.0114196 December 2, 2014IAA-Producing Yeasts in the Phyllosphere of the Carnivorous Plant nematodes [1]. Plants are populated by microorganisms below and above ground. Above-ground plant parts are typically colonized by microorganisms, such as different genera of bacteria, filamentous fungi, yeasts, algae, and, less frequently, protozoa and PLOS ONE | DOI:10.1371/journal.pone.0114196. Growth of microorganisms in the phyllosphere is dependent on nutrients from plant metabolites that are secreted to the plant surface, or on compounds from external sources that contact the plant surface. The availability of carbon-containing nutrients on leaves is a major determinant of epiphytic colonization. Simple sugars such as glucose, fructose, and sucrose are the dominant carbon sources in plants and leach from the interior of the plant [2]. Veins, and surface appendages, including trichomes and hydathodes, can all affect nutrient availability in the phyllosphere [3, 4]
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