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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.

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Many plant-ant interactions are considered mutualisms. In Mallotus paniculatus (Euphorbiaceae) (also known as Turn-in-the-wind), the extrafloral nectaries (EFNs) on the base of the leaf laminas can produce sugar-rich secretions to attract ants as effective agents against herbivores or plant competitors. Growing evidence reveals that microorganisms are important "hidden players" in insect-plant interactions. Understanding which microorganisms act as such third-party species and how they operate is a major challenge in the study of mutualistic interactions. In this study, we showed that two dominant fungal species, the yeast Jaminaea angkorensis and the hyphal fungus Gibellulopsis nigrescens both from EFNs and the interiors of bodies of the ant Pheidole megacephala (Formicidae) on their own were sufficient for ant attraction. Our results also revealed that different fungal species on the host plant influenced ant behavior differently. These results can be applied in agriculture to increase ants or herbivore predators to protect plant hosts using fungal baits. Moreover, they indicate that fungal odors represent the critical signal to establish the plant-microbe-insect interactions. The traditional plantdefender concept must be updated to include the role of microorganisms.