Colletotrichum graminicola, the causal agent of maize leaf anthracnose and stalk rot, differentiates a pressurized infection cell called an appressorium in order to invade the epidermal cell, and subsequently forms biotrophic and necrotrophic hyphae to colonize the host tissue. While the role of force in appressorial penetration is established (Bechinger et al., 1999), the involvement of cell wall-degrading enzymes (CWDEs) in this process and in tissue colonization is poorly understood, due to the enormous number and functional redundancy of these enzymes. The serine/threonine protein kinase gene SNF1 identified in Sucrose Non-Fermenting yeast mutants mediates de-repression of catabolite-repressed genes, including many genes encoding CWDEs. In this study, we identified and functionally characterized the SNF1 homolog of C. graminicola. Δsnf1 mutants showed reduced vegetative growth and asexual sporulation rates on media containing polymeric carbon sources. Microscopy revealed reduced efficacies in appressorial penetration of cuticle and epidermal cell wall, and formation of unusual medusa-like biotrophic hyphae by Δsnf1 mutants. Severe and moderate virulence reductions were observed on intact and wounded leaves, respectively. Employing RNA-sequencing we show for the first time that more than 2,500 genes are directly or indirectly controlled by Snf1 in necrotrophic hyphae of a plant pathogenic fungus, many of which encode xylan- and cellulose-degrading enzymes. The data presented show that Snf1 is a global regulator of gene expression and is required for full virulence.

During initial stages of microbial invasion, the extracellular space (apoplast) of plant cells is a vital battleground between plants and pathogens. The oomycete plant pathogens secrete an array of apoplastic carbohydrate active enzymes, which are central molecules for understanding the complex plant-oomycete interactions. Among them, pectin acetylesterase (PAE) plays a critical role in the pathogenesis of plant pathogens including bacteria, fungi, and oomycetes. Here, we demonstrated that Peronophythora litchii (syn. Phytophthora litchii) PlPAE5 suppresses litchi (Litchi chinensis) plant immunity by interacting with litchi lipid transfer protein 1 (LcLTP1). The LcLTP1-binding activity and virulence function of PlPAE5 depend on its PAE domain but not on its PAE activity. The high expression of LcLTP1 enhances plant resistance to oomycete and fungal pathogens, and this disease resistance depends on BRASSINOSTEROID INSENSITIVE 1-associated receptor kinase 1 (BAK1) and Suppressor of BIR1 (SOBIR1) in Nicotiana benthamiana. LcLTP1 activates the plant salicylic acid (SA) signaling pathway, while PlPAE5 subverts the LcLTP1-mediated SA signaling pathway by destabilizing LcLTP1. Conclusively, this study reports a virulence mechanism of oomycete PAE suppressing plant LTP-mediated SA immune signaling and will be instrumental for boosting plant resistance breeding.

The permanent organs of grapevines (Vitis vinifera L.), like those of other woody perennials, are colonized by various unrelated pathogenic ascomycete fungi secreting cell wall-degrading enzymes and phytotoxic secondary metabolites that contribute to host damage and disease symptoms. Trunk pathogens differ in the symptoms they induce and the extent and speed of damage. Isolates of the same species often display a wide virulence range, even within the same vineyard. This study focuses on Eutypa lata, Neofusicoccum parvum, and Phaeoacremonium minimum, causal agents of Eutypa dieback, Botryosphaeria dieback, and Esca, respectively. We sequenced 50 isolates from viticulture regions worldwide and built nucleotide-level, reference-free pangenomes for each species. Through examination of genomic diversity and pangenome structure, we analyzed intraspecific conservation and variability of putative virulence factors, focusing on functions under positive selection and recent gene family dynamics of contraction and expansion. Our findings reveal contrasting distributions of putative virulence factors in the core, dispensable, and private genomes of each pangenome. For example, carbohydrate active enzymes (CAZymes) were prevalent in the core genomes of each pangenome, whereas biosynthetic gene clusters were prevalent in the dispensable genomes of E. lata and P. minimum. The dispensable fractions were also enriched in Gypsy transposable elements and virulence factors under positive selection (polyketide synthase genes in E. lata and P. minimum, glycosyltransferases in N. parvum). Our findings underscore the complexity of the genomic architecture in each species and provide insights into their adaptive strategies, enhancing our understanding of the underlying mechanisms of virulence. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Downy mildew caused by Sclerospora graminicola is a systemic infectious disease affecting foxtail millet production in Africa and Asia. S. graminicola-infected leaves could be decomposed to a state where only the veins remain, resulting in a filamentous leaf tissue symptom. The aim of the present study was to investigate how S. graminicola influences the formation of the filamentous leaf tissue symptoms in hosts at the morphological and molecular levels. We discovered that vegetative hyphae expanded rapidly, with high biomass accumulated at the early stages of S. graminicola infection. In addition, S. graminicola could affect spikelet morphological development at the panicle branch differentiation stage to the pistil and stamen differentiation stage by interfering with hormones and nutrient metabolism in the host, resulting in hedgehog-like panicle symptoms. S. graminicola could acquire high amounts of nutrients from host tissues through secretion of β-glucosidase, endoglucanase, and pectic enzyme, and destroyed host mesophyll cells by mechanical pressure caused by rapid expansion of hyphae. At the later stages, S. graminicola could rapidly complete sexual reproduction through tryptophan, fatty acid, starch, and sucrose metabolism and subsequently produce numerous oospores. Oospore proliferation and development further damage host leaves via mechanical pressure, resulting in a large number of degraded and extinct mesophyll cells and, subsequently, malformed leaves with only veins left, that is, \"filamentous leaf tissue.\" Our study revealed the S. graminicola expansion characteristics from its asexual to sexual development stages, and the potential mechanisms via which the destructive effects of S. graminicola on hosts occur at different growth stages.

The aims of present works were to explore the difference in pulp breakdown of \'Fuyan\' and \'Dongbi\' longans and its relationship with cell wall metabolism. Comparison with \'Fuyan\' longan fruit, postharvest \'Dongbi\' longan fruit showed lower pulp breakdown index, lower activities of PE, PG, cellulase, β-Gal, XET, and lower expression levels of their corresponding genes. In addition, higher levels of cell wall polysaccharides including ISP, CSP, cellulose and hemicellulose were exhibited in \'Dongbi\' longan pulp. These findings implied that, the reduced activities of enzymes and the down-regulated expressions of genes-involved in cell wall disassembly were shown in \'Dongbi\' longan pulp, which might reduce the dissolution of polysaccharides and maintain a higher structural integrity in \'Dongbi\' longan pulp cell wall, and consequently the mitigated pulp breakdown was displayed in \'Dongbi\' longan during storage.

Compared with P. longanae-infected longan, 2, 4-dinitrophenol (DNP) treatment for P. longanae-infected longan displayed the lower levels of pulp firmness, cell wall materials, ionic-soluble pectin, covalent-soluble pectin, hemicellulose, or cellulose, but the higher amount of water-soluble pectin, the higher activities of cell wall-degrading enzymes (CWDEs) (PG, β-Gal, PME, Cx, and XET), and the higher transcript levels of CWDEs-related genes (DlPG1, DlPG2, Dlβ-Gal1, DlPME1, DlPME2, DlPME3, DlCx1, and DlXET30). On the contrary, ATP treatment for P. longanae-infected longan exhibited opposite effects. The above results imply that DNP accelerated P. longanae-induced pulp softening and breakdown of fresh longan, which was because DNP up-regulated the transcript levels of CWDEs-related genes, enhanced the CWDEs activities, and accelerated the degradation of cell wall polysaccharides (CWP). However, ATP suppressed longan pulp softening and breakdown caused by P. longanae, because ATP down-regulated the transcript levels of CWDEs-related genes, lowered the CWDEs activities, and reduced the CWP degradation.

Dickeya zeae is an aggressive bacterial phytopathogen that infects a wide range of host plants. It has been reported that integration host factor (IHF), a nucleoid-associated protein consisting of IHFα and IHFβ subunits, regulates gene expression by influencing nucleoid structure and DNA bending. To define the role of IHF in the pathogenesis of D. zeae MS2, we deleted either and both of the IHF subunit encoding genes ihfA and ihfB, which significantly reduced the production of cell wall-degrading enzymes (CWDEs), an unknown novel phytotoxin and the virulence factor-modulating (VFM) quorum-sensing (QS) signal, cell motility, biofilm formation, and thereafter the infection ability towards both potato slices and banana seedlings. To characterize the regulatory pathways of IHF protein associated with virulence, IHF binding sites (consensus sequence 5\'-WATCAANNNNTTR-3\') were predicted and 272 binding sites were found throughout the genome. The expression of 110 tested genes was affected by IHF. Electrophoretic mobility shift assay (EMSA) showed direct interaction of IhfA protein with the promoters of vfmE, speA, pipR, fis, slyA, prtD, hrpL, hecB, hcp, indA, hdaA, flhD, pilT, gcpJ, arcA, arcB, and lysR. This study clarified the contribution of IHF in the pathogenic process of D. zeae by controlling the production of VFM and putrescine QS signals, phytotoxin, and indigoidine, the luxR-solo system, Fis, SlyA, and FlhD transcriptional regulators, and secretion systems from type I to type VI. Characterization of the regulatory networks of IHF in D. zeae provides a target for prevention and control of plant soft rot disease.

BACKGROUND: Microalgae are coming to the spotlight due to their potential applications in a wide number of fields ranging from the biofuel to the pharmaceutical sector. However, several factors such as low productivity, expensive harvesting procedures and difficult metabolite extractability limit their full utilization at industrial scale. Similarly to the successful employment of enzymatic arsenals from lignocellulolytic fungi to convert lignocellulose into fermentable sugars for bioethanol production, specific algalytic formulations could be used to improve the extractability of lipids from microalgae to produce biodiesel. Currently, the research areas related to algivorous organisms, algal saprophytes and the enzymes responsible for the hydrolysis of algal cell wall are still little explored.
RESULTS: Here, an algal trap method for capturing actively growing microorganisms was successfully used to isolate a filamentous fungus, that was identified by whole-genome sequencing, assembly and annotation as a novel Penicillium sumatraense isolate. The fungus, classified as P. sumatraense AQ67100, was able to assimilate heat-killed Chlorella vulgaris cells by an enzymatic arsenal composed of proteases such as dipeptidyl- and amino-peptidases, β-1,3-glucanases and glycosidases including α- and β-glucosidases, β-glucuronidase, α-mannosidases and β-galactosidases. The treatment of C. vulgaris with the filtrate from P. sumatraense AQ67100 increased the release of chlorophylls and lipids from the algal cells by 42.6 and 48.9%, respectively.
CONCLUSIONS: The improved lipid extractability from C. vulgaris biomass treated with the fungal filtrate highlighted the potential of algal saprophytes in the bioprocessing of microalgae, posing the basis for the sustainable transformation of algal metabolites into biofuel-related compounds.

Fusarium is an important plant pathogen and many cell wall-degrading enzymes (CWDEs) are produced in Fusarium-infected plant tissues. To investigate the role of CWDEs in the pathogenicity of pitaya pathogen, we isolated a Fusarium equiseti strain from the diseased pitaya fruit and the activities of CWDEs were determined. The higher polygalacturonase (PG) activity was confirmed both in vitro and vivo. Aiming at the PG gene, the CRISPR/Cas9 system of F. equiseti was constructed and optimized for the first time. Through the process of microhomology-mediated end joining, the flanking region containing 30 bp was used to mediate the homologous recombination of Cas9 double-strand breaks, and the PG gene knockout mutants were obtained by protoplast transformation. Through the phenotypic and pathogenicity experiments of the wild-type strain and mutant strain, the results showed that the colony growth rate and spore production of the strain without the PG gene decreased to some extent, and the lesion diameter and the degree of pericarp cell damage decreased, which showed that the CRISPR/Cas9 system could be used in F. equiseti and PG enzyme and can play a significant role in the interaction between F. equiseti and pitaya fruit.

Many fungi differentiate specific infection structures in order to infect the host plant. The spore attaches to the host surface, the cuticle, and the germ tube may recognize suitable penetration sites, over which an appressorium is formed. Additional wall layers in appressoria of many fungi suggest that this structure supports increasing pressure during the penetration process. During appressorium formation, synthesis of polymer-degrading enzymes is often initiated. Cutinases, cellulases and pectin-degrading enzymes can be formed in a developmentally controlled or adaptive, i.e. substrate-dependent, fashion. The penetration hypha develops below the appressorium. This hypha has a new wall structure and exhibits features which serve to breach the plant cell wall. However, at present it is not clear whether penetration hyphae arising from appressoria are more efficient in penetration or induce less damage than hyphae which penetrate without detectable special adaptations. The infection hypha differentiates within the host. During differentiation a characteristic set of enzymes is synthesized to enable successful establishment of the host-pathogen relationship. If, as in most cases, multiple forms of cell wall-degrading enzymes are formed by the pathogen, mutagenesis or deletion of a gene encoding one of these enzymes very often has no effect on pathogenicity or even virulence. Proof is missing very often that an enzyme is needed at the right time and at the right site of infection. Events occurring during differentiation of fungal infection structures are reviewed with special emphasis on Magnaporthe grisea, Colletotrichum spp., and rust fungi, and common features which may be of importance to the success of infection are discussed. CONTENTS Summary 193 I. Introduction 193 II. Spore and germ tube 195 III. The appressorium 199 IV. The penetration hypha 201 V. The infection hypha 204 VI. Future prospects 208 Acknowledgements 208 References 208.