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Soil-inhabiting fungal pathogens use chemical signals released by roots to direct hyphal growth towards the host plant. Whether other soil microorganisms exploit this capacity for their own benefit is currently unknown. Here we show that the endophytic rhizobacterium Rahnella aquatilis locates hyphae of the root-infecting fungal pathogen Fusarium oxysporum through pH-mediated chemotaxis and uses them as highways to efficiently access and colonize plant roots. Secretion of gluconic acid (GlcA) by R. aquatilis in the rhizosphere leads to acidification and counteracts F. oxysporum-induced alkalinisation, a known virulence mechanism, thereby preventing fungal infection. Genetic abrogation or biochemical inhibition of GlcA-mediated acidification abolished biocontrol activity of R. aquatilis and restored fungal infection. These findings reveal a new way by which bacterial endophytes hijack hyphae of a fungal pathogen in the soil to gain preferential access to plant roots, thereby protecting the host from infection.

Abstract-Traceability recovery is a key software maintenance activity in which software engineers extract the relationships among software artifacts. Information Retrieval (IR) has been widely accepted as a method for automated traceability recovery based on the textual similarity among the software artifacts. However, a notorious difficulty for IR-based methods is that artifacts may be related even if they are not textually similar. A growing body of work addresses this challenge by combining IR-based methods with structural information from source code. Unfortunately, the accuracy of such methods is highly dependent on the IR methods. If IR methods perform poorly, the combined approaches may perform even worse.In this paper, we propose to use the feedback provided by software engineers when classifying candidate links to regulate the effect of using structural information. Specifically, our approach only considers structural information when the traceability links from the IR methods are verified by developers and classified as correct links. An empirical evaluation conducted on three systems suggests that our approach outperforms both a pure IR-based method and a simple approach for combining textual and structural information.

The use of synthetic fungicides to control fungal diseases has growing limitations due to eco-toxicological risks. Therefore, it is necessary to replace or integrate high risk chemicals with safer tools for human health and environment. Consequently, research on the selection, evaluation, characterization, and use of biocontrol agents (BCAs) has consistently increased in the last decades. BCA formulates, particularly in some countries, are still scarce in coping with the growing demand for their use in sustainable agricultural management. To foster development and utilization of new effective bioformulates, there is a need to optimize BCA activity, to share knowledge on their formulation processes and to simplify the registration procedures. Studies based on new molecular tools can significantly contribute to achieve such objectives. The present review provides the state of the art on biocontrol of fungal plant diseases with special emphasis on (i) features of the most studied BCAs; (ii) key strategies to optimize selection and use of BCAs (iii); mechanisms of action of the main BCAs; (iv) molecular tools and metagenomic studies in the selection and use of BCAs; (v) main issues and constraints in the registration and commercialization of BCAs, and (vi) perspectives in the biocontrol of fungal plant diseases.

Fungal attacks on stored vegetable and fruits 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 yap1Δ and rim101Δ mutants display decreased ability to colonize wounded fruit as compared to the parental WT strain; the yap1Δ mutant also displays reduced biocontrol activity against the postharvest pathogens Penicillium expansum and Monilia 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 LS28 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 fruits, 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 genomics and genetics resources to investigate at 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.

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