Molecular Tools for the Yeast Papiliotrema terrestris LS28 and Identification of Yap1 as a Transcription Factor Involved in Biocontrol Activity

The use of fungicides represents the most effective and widely used strategy for controlling postharvest diseases. However, their extensive use has raised several concerns, such as the emergence of plant pathogens' resistance as well as the health risks associated with the persistence of chemical residues in fruits, vegetables, and the environment. ABSTRACT Fungal attacks on stored fruit and vegetables are responsible for losses of products. There is an active research field to develop alternative strategies for postharvest disease management, and the use of biocontrol agents represents a promising approach. Understanding the molecular bases of the biocontrol activity of these agents is crucial to potentiate their effectiveness. The yeast Papiliotrema terrestris is a biocontrol agent against postharvest pathogens. Phenotypic studies suggest that it exerts its antagonistic activity through competition for nutrients and space, which relies on its resistance to oxidative and other cellular stresses. In this study, we developed tools for genetic manipulation in P. terrestris to perform targeted gene replacement and functional complementation of the transcription factors Yap1 and Rim101. In vitro phenotypic analyses revealed a conserved role of Yap1 and Rim101 in broad resistance to oxidative stress and alkaline pH sensing, respectively. In vivo analyses revealed that P. terrestris yap1 Δ and rim101 Δ mutants display decreased ability to colonize wounded fruit compared to that of the parental wild-type (WT) strain; the yap1 Δ mutant also displays reduced biocontrol activity against the postharvest pathogens Penicillium expansum and Monilinia fructigena , indicating an important role for resistance to oxidative stress in timely wound colonization and biocontrol activity of P. terrestris . In conclusion, the availability of molecular tools developed in the present study provides a foundation to elucidate the genetic mechanisms underlying biocontrol activity of P. terrestris , with the goal of enhancing this activity for the practical use of P. terrestris in pest management programs based on biological and integrated control. IMPORTANCE The use of fungicides represents the most effective and widely used strategy for controlling postharvest diseases. However, their extensive use has raised several concerns, such as the emergence of plant pathogens' resistance as well as the health risks associated with the persistence of chemical residues in fruit, in vegetables, and in the environment. These factors have brought attention to alternative methods for controlling postharvest diseases, such as the utilization of biocontrol agents. In the present study, we developed genetic resources to investigate at the molecular level the mechanisms involved in the biocontrol activity of Papiliotrema terrestris , a basidiomycete yeast that is an effective biocontrol agent against widespread fungal pathogens, including Penicillium expansum , the etiological agent of blue mold disease of pome fruits. A deeper understanding of how postharvest biocontrol agents operate is the basic requirement to promote the utilization of biological (and integrated) control for the reduction of chemical fungicides.