Disease severity enhancement by an esterase from non-phytopathogenic yeast Pseudozyma antarctica and its potential as adjuvant for biocontrol agents

Life on a leaf: the epiphyte to pathogen continuum and interplay in the phyllosphere

Epiphytic microbes are those that live for some or all of their life cycle on the surface of plant leaves. Leaf surfaces are a topologically complex, physicochemically heterogeneous habitat that is home to extensive, mixed communities of resident and transient inhabitants from all three domains of life. In this review, we discuss the origins of leaf surface microbes and how different biotic and abiotic factors shape their communities. We discuss the leaf surface as a habitat and microbial adaptations which allow some species to thrive there, with particular emphasis on microbes that occupy the continuum between epiphytic specialists and phytopathogens, groups which have considerable overlap in terms of adapting to the leaf surface and between which a single virulence determinant can move a microbial strain. Finally, we discuss the recent findings that the wheat pathogenic fungus Zymoseptoria tritici spends a considerable amount of time on the leaf surface, and ask what insights other epiphytic organisms might provide into this pathogen, as well as how Z. tritici might serve as a model system for investigating plant-microbe-microbe interactions on the leaf surface.

Cutinase-like biodegradable plastic-degrading enzymes from phylloplane yeasts have cutinase activity

Phylloplane yeast genera Pseudozyma and Cryptococcus secrete biodegradable plastic (BP)-degrading enzymes, termed cutinase-like enzymes (CLEs). Although CLEs contain highly conserved catalytic sites, the whole protein exhibits ≤30% amino acid sequence homology with cutinase. In this study, we analyzed whether CLEs exhibit cutinase activity. Seventeen Cryptococcus magnus strains, which degrade BP at 15 °C, were isolated from leaves and identified the DNA sequence of the CLE in one of the strains. Cutin was prepared from tomato leaves and treated with CLEs from 3 Cryptococcus species (C. magnus, Cryptococcus flavus, and Cryptococcus laurentii) and Pseudozyma antarctia (PaE). A typical cutin monomer, 10,16-dihydroxyhexadecanoic acid, was detected in extracts of the reaction solution via gas chromatography-mass spectrometry, showing that cutin was indeed degraded by CLEs. In addition to the aforementioned monomer, separation analysis via thin-layer chromatography detected high-molecular-weight products resulting from the breakdown of cutin by PaE, indicating that PaE acts as an endo-type enzyme.

Shaping the leaf microbiota: plant-microbe-microbe interactions

The aerial portion of a plant, namely the leaf, is inhabited by pathogenic and non-pathogenic microbes. The leaf's physical and chemical properties, combined with fluctuating and often challenging environmental factors, create surfaces that require a high degree of adaptation for microbial colonization. As a consequence, specific interactive processes have evolved to establish a plant leaf niche. Little is known about the impact of the host immune system on phyllosphere colonization by non-pathogenic microbes. These organisms can trigger plant basal defenses and benefit the host by priming for enhanced resistance to pathogens. In most disease resistance responses, microbial signals are recognized by extra- or intracellular receptors. The interactions tend to be species specific and it is unclear how they shape leaf microbial communities. In natural habitats, microbe-microbe interactions are also important for shaping leaf communities. To protect resources, plant colonizers have developed direct antagonistic or host manipulation strategies to fight competitors. Phyllosphere-colonizing microbes respond to abiotic and biotic fluctuations and are therefore an important resource for adaptive and protective traits. Understanding the complex regulatory host-microbe-microbe networks is needed to transfer current knowledge to biotechnological applications such as plant-protective probiotics.

Determination of residue of diflufenican in wheat and soil by ultra-high-pressure liquid chromatography and mass spectrometry conditions

BACKGROUND

In order to clarify whether the application of diflufenican in the wheat field will produce residues in wheat plants and soil. In this experiment, ultra-high-pressure liquid chromatography was used to determine the residues of diflufenican in wheat plants, grains, and soil, which provided a new theoretical basis and technical guidance for the safe production of wheat.

RESULTS

The results showed that the average diflufenican recovery per added level in wheat and soil were in the range of 85.7% to 91.3%, relative standard deviations were all in a range of 2.43% to 6.00%, and the minimum detectable amount of diflufenican was 1.0 × 10^-10  g kg^-1 . With the increase of wheat growing days and soil layers, the residues of diflufenican in wheat plants and soil became lower. The order of residual amount of diflufenican in the growth period were heading period, flowering period, filling period and maturing period. The order of residual amount of diflufenican in different soil layers was 0-20, 20-40, 40-60, 60-80 and 80-100 cm respectively from the top to the bottom. In addition, with the increase of the dosage of diflufenican, the residual amount of diflufenican becomes higher. Thus, the residual amount of diflufenican after 2.0 times applied amount was higher than the 1.0 time applied amount.

CONCLUSION

The residual amounts of diflufenican in wheat and soil were very small, far below the value of the maximum residue limit (MRL) on wheat provided by China. Under the applied amount administered in this experiment, a single spray of diflufenican in wheat trifoliate is safe for wheat, humans and livestock. © 2020 Society of Chemical Industry.

A brief from the leaf: latest research to inform our understanding of the phyllosphere microbiome

The plant leaf surface, or phyllosphere, represents a unique and challenging microbial biome with a diverse and dynamic community of commensal, parasitic, and mutualistic agents of microscopic proportions. This mini-review offers a digest of recently published research dedicated to the study of phyllosphere microbiota, framed in the context of processes and outcomes of microbial community assembly, structure, and (inter)activity in the phyllosphere, with particular focus on the contributions of environment, plant, and microbe, and on the potential benefits of interrogating those contributions at finer resolutions.

The phylloplane yeast Pseudozyma: a rich potential for biotechnology

Basidiomycetous yeast Pseudozyma strains are often isolated from leaf surfaces. Here, we describe the sources of Pseudozyma yeasts and their useful secreted products, including enzymes and biosurfactants. We then outline the life of Pseudozyma on the leaf surface and introduce studies to verify ecological functions of their useful products. In addition, the function of Pseudozyma in maintaining the health of plants is briefly explained. Finally, the gene manipulation techniques necessary for future research and development of technological applications of Pseudozyma are described.