Twinfilin regulates actin assembly and Hexagonal peroxisome 1 (Hex1) localization in the pathogenesis of rice blast fungus Magnaporthe oryzae

Molecular Characterisation of the Peroxidase Gene Family in Botrytis cinerea and the Role of BcPRD7 in Virulence

Peroxidase activity is essential for the virulence of a number of plant-pathogenic fungi. However, there are few reports of the systematic analysis of peroxidase genes in Botrytis cinerea. We identified all the peroxidase genes of B. cinerea by searching the fungal peroxidase database and found that the expression levels of BcPRD3, BcPRD7, BcPRD8 and BcPRD10 changed significantly during hyphal development and in response to H2O2 stress treatment and infection of Arabidopsis thaliana by B. cinerea. We found that the hyphae of the mutant strains became more slender, the number and size of the infection structures decreased, the number of conidia decreased and the stress response and virulence decreased significantly. These four genes positively regulated the growth, development and pathogenicity of B. cinerea and participated in osmotic and oxidative stress response and cell integrity maintenance. In addition, we also found that BcPRD7 played important roles in oxidase enzyme activity, ion penetration, the synthesis and metabolism of mycotoxins, and determined the interaction between BcPRD7 and BcHEX, the latter being the major protein of the Woronin body. It is speculated that BcPRD7 may regulate the growth, development and pathogenicity of the pathogen by participating in the development of the Woronin body. The function of peroxidase family genes in B. cinerea was systematically analysed in this study, which provides a solid foundation for the subsequent in-depth elucidation of the relevant regulatory mechanisms and is expected to provide new ideas and strategies for the prevention and control of B. cinerea diseases.

The Magnaporthe oryzae effector MoBys1 suppresses rice immunity by targeting OsCAD2 to manipulate host jasmonate and lignin metabolism

Rice blast disease caused by Magnaporthe oryzae poses a severe threat to rice production. To counteract M. oryzae, plants synthesize jasmonate (JA) and lignin, two primary defense-related metabolites, to initiate defense programs. However, the mechanism through which M. oryzae modulates JA- and lignin-mediated plant immunity remains unclear. In this study, a novel M. oryzae effector, MoBys1, was identified as being involved in pathogenesis. Knockout of MoBys1 in M. oryzae significantly reduced its infection ability. Conversely, overexpression of MoBys1 in rice impaired the rice defense response. MoBys1 localizes to the plant cytoplasm and nucleus and interacts with rice cinnamyl alcohol dehydrogenase 2 (OsCAD2), an enzyme that catalyzes lignin biosynthesis. While OsCAD2 mutants exhibited weakened defenses, overexpression lines demonstrated enhanced resistance, highlighting the critical role of OsCAD2 in blast resistance. Furthermore, OsCAD2 functions as a transcription factor regulating a wide range of biological processes, including JA and lignin signaling pathways. The interaction between MoBys1 and OsCAD2 promotes OsCAD2 degradation, leading to reduced lignin and JA accumulation. These findings uncover a novel counter-defense mechanism by which M. oryzae employs the effector MoBys1 to degrade OsCAD2 and suppress host defense-related metabolite accumulation during infection.

The curtain model as an alternative and complementary to the classic turgor concept of filamentous fungi

Turgor pressure is critically important for all organisms with the cell wall. In fungi, turgor is involved in the apical growth of hyphae, affects cell size, provides tension to the plasma membrane, creates the necessary rigidity for hyphae to penetrate the substrate, and has many other functions. However, there is increasing evidence that turgor pressure is not always the sole or main factor influencing some of these processes. This review characterizes the curtain model, previously proposed to describe the regulation of plasma membrane tension in the hyphae of basidiomycetes. The current understanding of the four main components of the model is outlined: the driving actin cytoskeleton, the elastic cell wall, tight adhesion of the plasma membrane to the cell wall, and macroinvaginations of the plasma membrane. All four elements, as a single model, complement or replace some physiological functions of turgor and allow us to understand how a non-apical fungal cell maintains its physiological functionality under changing environmental conditions. Further experimental confirmation of this model is fundamentally important for mycology and applied sciences.

The Microtubule End Binding Protein Mal3 Is Essential for the Dynamic Assembly of Microtubules during Magnaporthe oryzae Growth and Pathogenesis

Cytoskeletal microtubules (MTs) play crucial roles in many aspects of life processes in eukaryotic organisms. They dynamically assemble physiologically important MT arrays under different cell conditions. Currently, aspects of MT assembly underlying the development and pathogenesis of the model plant pathogenic fungus Magnaporthe oryzae (M. oryzae) are unclear. In this study, we characterized the MT plus end binding protein MoMal3 in M. oryzae. We found that knockout of MoMal3 results in defects in hyphal polar growth, appressorium-mediated host penetration and nucleus division. Using high-resolution live-cell imaging, we further found that the MoMal3 mutant assembled a rigid MT in parallel with the MT during hyphal polar growth, the cage-like network in the appressorium and the stick-like spindle in nuclear division. These aberrant MT organization patterns in the MoMal3 mutant impaired actin-based cell growth and host infection. Taken together, these findings showed that M. oryzae relies on MoMal3 to assemble elaborate MT arrays for growth and infection. The results also revealed the assembly mode of MTs in M. oryzae, indicating that MTs are pivotal for M. oryzae growth and host infection and may be new targets for devastating fungus control.

Fimbrin associated with Pmk1 to regulate the actin assembly during Magnaporthe oryzae hyphal growth and infection

The dynamic assembly of the actin cytoskeleton is vital for Magnaporthe oryzae development and host infection. The actin-related protein MoFim1 is a key factor for organizing the M. oryzae actin cytoskeleton. Currently, how MoFim1 is regulated in M. oryzae to precisely rearrange the actin cytoskeleton is unclear. In this study, we found that MoFim1 associates with the M. oryzae mitogen-activated protein (MAP) kinase Pmk1 to regulate actin assembly. MoFim1 directly interacted with Pmk1, and the phosphorylation level of MoFim1 was decreased in Δpmk1, which led to a change in the subcellular distribution of MoFim1 in the hyphae of Δpmk1. Moreover, the actin cytoskeleton was aberrantly organized at the hyphal tip in the Δpmk1, which was similar to what was observed in the Δmofim1 during hyphal growth. Furthermore, phosphorylation analysis revealed that Pmk1 could phosphorylate MoFim1 at serine 94. Loss of phosphorylation of MoFim1 at serine 94 decreased actin bundling activity. Additionally, the expression of the site mutant of MoFim1 S94D (in which serine 94 was replaced with aspartate to mimic phosphorylation) in Δpmk1 could reverse the defects in actin organization and hyphal growth in Δpmk1. It also partially rescues the formation of appressorium failure in Δpmk1. Taken together, these findings suggest a regulatory mechanism in which Pmk1 phosphorylates MoFim1 to regulate the assembly of the actin cytoskeleton during hyphal development and pathogenesis.

Magnaporthe oryzae Transcription Factor MoBZIP3 Regulates Appressorium Turgor Pressure Formation during Pathogenesis

The devastating fungus Magnaporthe oryzae (M. oryzae) forms a specialized infection structure known as appressorium, which generates enormous turgor, to penetrate the plant cells. However, how M. oryzae regulates the appressorium turgor formation, is not well understood. In this study, we identified MoBZIP3, a bZIP transcription factor that functioned in pathogenesis in M. oryzae. We found that the pathogenicity of the MoBZIP3 knockout strain (Δmobzip3) was significantly reduced, and the defect was restored after re-expression of MoBZIP3, indicating that MoBZIP3 is required for M. oryzae virulence. Further analysis showed that MoBZIP3 functions in utilization of glycogen and lipid droplets for generation of glycerol in appressorium. MoBZIP3 localized in the nucleus and could bind directly to the promoters of the glycerol synthesis-related genes, MoPTH2, MoTGL1 and MoPEX6, and regulate their expression which is critical for glycerol synthesis in the appressorium turgor pressure generation. Furthermore, the critical turgor sensor gene MoSln1 was also down regulated and its subcellular localization was aberrant in Δmobzip3, which leads to a disordered actin assembly in the Δmobzip3 appressorium. Taken together, these results revealed new regulatory functions of the bZIP transcription factor MoBZIP3, in regulating M. oryzae appressorium turgor formation and infection.