An actin mechanostat ensures hyphal tip sharpness in Phytophthora infestans to achieve host penetration

From glycans to green biotechnology: exploring cell wall dynamics and phytobiota impact in plant glycopathology

Filamentous plant pathogens, including fungi and oomycetes, pose significant threats to cultivated crops, impacting agricultural productivity, quality and sustainability. Traditionally, disease control heavily relied on fungicides, but concerns about their negative impacts motivated stakeholders and government agencies to seek alternative solutions. Biocontrol agents (BCAs) have been developed as promising alternatives to minimize fungicide use. However, BCAs often exhibit inconsistent performances, undermining their efficacy as plant protection alternatives. The eukaryotic cell wall of plants and filamentous pathogens contributes significantly to their interaction with the environment and competitors. This highly adaptable and modular carbohydrate armor serves as the primary interface for communication, and the intricate interplay within this compartment is often mediated by carbohydrate-active enzymes (CAZymes) responsible for cell wall degradation and remodeling. These processes play a crucial role in the pathogenesis of plant diseases and contribute significantly to establishing both beneficial and detrimental microbiota. This review explores the interplay between cell wall dynamics and glycan interactions in the phytobiome scenario, providing holistic insights for efficiently exploiting microbial traits potentially involved in plant disease mitigation. Within this framework, the incorporation of glycobiology-related functional traits into the resident phytobiome can significantly enhance the plant's resilience to biotic stresses. Therefore, in the rational engineering of future beneficial consortia, it is imperative to recognize and leverage the understanding of cell wall interactions and the role of the glycome as an essential tool for the effective management of plant diseases.

A fitness landscape instability governs the morphological diversity of tip-growing cells

Cellular morphology affects many aspects of cellular and organismal physiology. This makes it challenging to dissect the evolutionary basis for specific morphologies since various cellular functions may exert competing selective pressures on this trait, and the influence of these pressures will depend on the specific mechanisms of morphogenesis. In this light, we combined experiment and theory to investigate the complex basis for morphological diversity among tip-growing cells from across the tree of life. We discovered that an instability in the widespread mechanism of "inflationary" tip growth leads directly to a bifurcation in the common fitness landscape of tip-growing cells, which imposes a strict global constraint on their morphologies. This result rationalizes the morphology of an enormous diversity of important fungal, plant, protistan, and bacterial systems. More broadly, our study elucidates the principle that strong evolutionary constraints on complex traits, like biological form, may emerge from emergent instabilities within developmental systems.

Myosin F controls actin organization and dynamics in Toxoplasma gondii

Intracellular cargo transport is a ubiquitous cellular process in all eukaryotes. In many cell types, membrane bound cargo is associated with molecular motors which transport cargo along microtubule and actin tracks. In Toxoplasma gondii (T. gondii), an obligate intracellular parasite in the phylum Apicomplexa, organization of the endomembrane pathway depends on actin and an unconventional myosin motor, myosin F (MyoF). Loss of MyoF and actin disrupts vesicle transport, organelle positioning, and division of the apicoplast, a nonphotosynthetic plastid organelle. How this actomyosin system contributes to these cellular functions is still unclear. Using live-cell imaging, we observed that MyoF-EmeraldFP (MyoF-EmFP) displayed a dynamic and filamentous-like organization in the parasite cytosol, reminiscent of cytosolic actin filament dynamics. MyoF was not associated with the Golgi, apicoplast or dense granule surfaces, suggesting that it does not function using the canonical cargo transport mechanism. Instead, we found that loss of MyoF resulted in a dramatic rearrangement of the actin cytoskeleton in interphase parasites accompanied by significantly reduced actin dynamics. However, actin organization during parasite replication and motility was unaffected by the loss of MyoF. These findings revealed that MyoF is an actin organizing protein in Toxoplasma and facilitates cargo movement using an unconventional transport mechanism.

Cell-type-specific responses to fungal infection in plants revealed by single-cell transcriptomics

Pathogen infection is a dynamic process. Here, we employ single-cell transcriptomics to investigate plant response heterogeneity. By generating an Arabidopsis thaliana leaf atlas encompassing 95,040 cells during infection by a fungal pathogen, Colletotrichum higginsianum, we unveil cell-type-specific gene expression, notably an enrichment of intracellular immune receptors in vasculature cells. Trajectory inference identifies cells that had different interactions with the invading fungus. This analysis divulges transcriptional reprogramming of abscisic acid signaling specifically occurring in guard cells, which is consistent with a stomatal closure dependent on direct contact with the fungus. Furthermore, we investigate the transcriptional plasticity of genes involved in glucosinolate biosynthesis in cells at the fungal infection sites, emphasizing the contribution of the epidermis-expressed MYB122 to disease resistance. This work underscores spatially dynamic, cell-type-specific plant responses to a fungal pathogen and provides a valuable resource that supports in-depth investigations of plant-pathogen interactions.

Regulation of Intracellular Reactive Oxygen Species Levels after the Development of Phallus rubrovolvatus Rot Disease Due to Trichoderma koningii Mycoparasitism

Phallus rubrovolvatus is a unique mushroom used for medicinal and dietary purposes in China. In recent years, however, the rot disease of P. rubrovolvatus has seriously affected its yield and quality, becoming an economically important threat. In this study, samples of symptomatic tissues were collected, isolated, and identified from five major P. rubrovolvatus production regions in Guizhou Province, China. Based on combined analyses of phylogenies (ITS and EF1-α), morphological characteristics and Koch's postulates, Trichoderma koningiopsis and Trichoderma koningii were identified as the pathogenic fungal species. Among these, T. koningii exhibited stronger pathogenicity than the other strains; thus, T. koningii was used as the test strain in the follow-up experiments. Upon co-culturing T. koningii with P. rubrovolvatus, the hyphae of the two species were intertwined, and the color of the P. rubrovolvatus hyphae changed from white to red. Moreover, T. koningii hyphae were wrapped around P. rubrovolvatus hyphae, leading to their shortening and convolution and ultimately inhibiting their growth due to wrinkling; T. koningii penetrated the entire basidiocarp tissue of P. rubrovolvatus, causing serious damage to the host basidiocarp cells. Further analyses revealed that T. koningii infection resulted in the swelling of basidiocarps and significantly enhanced the activity of defense-related enzymes, such as malondialdehyde, manganese peroxidase, and polyphenol oxidase. These findings offer theoretical support for further research on the infection mechanisms of pathogenic fungi and the prevention of diseases caused by them.

Fatal attraction: How Phytophthora zoospores find their host

Oomycete plant pathogens, such as Phytophthora and Pythium species produce motile dispersal agents called zoospores that actively target host plants. Zoospores are exceptional in their ability to display taxis to chemical, electrical and physical cues to navigate the phyllosphere and reach stomata, wound sites and roots. Many components of root exudates have been shown attractive or repulsive to zoospores. Although some components possess very strong attractiveness, it seems that especially the mix of components exuded by the primary host is most attractive to zoospores. Zoospores actively approach attractants with swimming behaviour reminiscent of other microswimmers. To achieve a unified description of zoospore behaviour when sensing an attractant, we propose the following terms for the successive stages of the homing response: reorientation, approaching, retention and settling. How zoospores sense and process attractants is poorly understood but likely involves signal perception via cell surface receptors. Since zoospores are important for infection, undermining their activity by luring attractants or blocking receptors seem promising strategies for disease control.