Pest categorisation of Fusarium oxysporum f. sp. cubense Tropical Race 4

A novel key virulence factor, FoSSP71, inhibits plant immunity and promotes pathogenesis in Fusarium oxysporum f. sp. cubense

Fusarium wilt of banana (Musa spp.), caused by Fusarium oxysporum f. sp. cubense (Foc), poses a significant threat to the global banana industry. Particularly, tropical race 4 of Foc exhibits high pathogenicity toward the major commercial banana cultivar Cavendish, and there are no effective control measures available. Here, we characterize a novel effector protein, FoSSP71, from Foc, which was significantly induced during the early stages of the Foc4 banana interaction and could suppress BAX-triggered programmed cell death in Nicotiana benthamiana. Transient expression of FoSSP71 in N. benthamiana leaves could weaken the upregulation expression of genes involved in the SA signaling pathway induced by flg22 and significantly reduce both reactive oxygen species bursts and callose accumulation. To verify the function of FoSSP71, a FoSSP71 deletion mutant was created. The FoSSP71 deletion mutant displayed a reduced growth rate in F. oxysporum and a marked reduction in virulence toward bananas compared to the wild type (WT). Furthermore, the expression levels of PR3 and PR10 were significantly downregulated in bananas infected with the ΔFoSSP71 strain compared to bananas infected with the WT strain. These findings indicate that FoSSP71 is essential for Foc4 pathogenicity and plays a key virulence role during Fusarium invasion. Therefore, FoSSP71 presents a potential target for future Fusarium wilt control, offering a scientific foundation for breeding disease-resistant banana varieties and developing novel control measures.IMPORTANCEEffector proteins are critical virulence factors for fungi, playing essential roles during the fungal infection of plants. In this study, we identified a novel effector protein, FoSSP71, which is an important regulatory protein involved in the invasion of bananas by Fusarium oxysporum f. sp. cubense race 4 (Foc4). Understanding its regulatory mechanisms is necessary. Our research indicates that FoSSP71 is an essential virulence factor for Foc4, as it suppresses plant immune responses by inhibiting the accumulation of reactive oxygen species and callose. The Foc4 mutant lacking FoSSP71 showed significantly reduced pathogenicity toward bananas, demonstrating that FoSSP71 is a potential target for controlling banana wilt disease. These findings provide a scientific basis for breeding banana varieties resistant to wilt disease and for developing new disease control strategies, which are crucial for the sustainable development of the global banana industry.

Optimization of a CRISPR-Cas9 in vitro protocol for targeting the SIX9 gene of Fusarium oxysporum f.sp. cubense race 1 associated with banana Fusarium wilt

Introduction

Fusarium wilt of bananas (Musa spp.), a threat to sustainable banana production worldwide, necessitates immediate action to control the disease. The current strategies are centered on preventing its spread or developing resistant varieties. However, very little is known about the genetic machinery used by the fungus to infect and kill banana plants. Therefore, research should the focused also in understanding the plant-pathogen molecular interaction by targeting virulent genes for knock-out in Fusarium. This study aims to standardize a gene editing protocol using CRISPR Cas9 technology in Fusarium oxysporum f.sp. cubense race 1 (Foc1); specifically, to induce targeted mutations on a particular effector gene, SIX9, of Foc1.

Methods

An in vitro protocol was optimized for the production of the Cas9 protein to target the SIX9 gene testing two gRNAs, by expression and purification of the Cas9, included in plasmids pHis-parallel1 and pMJ922, in E. coli BL21 Rosetta, independently.

Results

Results demonstrated that the produced Cas9 exhibits high enzymatic activity, comparable to the commercial standard. These findings underscore the robustness of the in-house enzyme and highlight its suitability for future research and biotechnological applications.

Discussion

This protocol facilitates the production of recombinant Cas9, enabling its use in various experimental settings and accelerating research in targeted gene editing, an area of significant relevance today. This protocol will support future studies on banana-Fusarium interaction by identifying candidate genes for disease resistance for the plant, or lack of virulence for the pathogen, by establishing the function of SIX effector proteins and evaluating the fungus's infection capacity through pathogenicity assays.

A Network of Sporogenesis-Responsive Genes Regulates the Growth, Asexual Sporogenesis, Pathogenesis and Fusaric Acid Production of Fusarium oxysporum f. sp. cubense

The conidia produced by Fusarium oxysporum f. sp. cubense (Foc), the causative agent of Fusarium Wilt of Banana (FWB), play central roles in the disease cycle, as the pathogen lacks a sexual reproduction process. Until now, the molecular regulation network of asexual sporogenesis has not been clearly understood in Foc. Herein, we identified and functionally characterized thirteen (13) putative sporulation-responsive genes in Foc, namely FocmedA(a), FocmedA(b), abaA-L, FocflbA, FocflbB, FocflbC, FocflbD, FocstuA, FocveA, FocvelB, wetA-L, FocfluG and Foclae1. We demonstrated that FocmedA(a), abaA-L, wetA-L, FocflbA, FocflbD, FocstuA, FocveA and Foclae1 mediate conidiophore formation, whereas FocmedA(a) and abaA-L are important for phialide formation and conidiophore formation. The expression level of abaA-L was significantly decreased in the ΔFocmedA(a) mutant, and yeast one-hybrid and ChIP-qPCR analyses further confirmed that FocMedA(a) could bind to the promoter of abaA-L during micro- and macroconidiation. Moreover, the transcript abundance of the wetA-L gene was significantly reduced in the ΔabaA-L mutant, and it not only was found to function as an activator of micro- and macroconidium formation but also served as a repressor of chlamydospore production. In addition, the deletions of FocflbB, FocflbC, FocstuA and Foclae1 resulted in increased chlamydosporulation, whereas FocflbD and FocvelB gene deletions reduced chlamydosporulation. Furthermore, FocflbC, FocflbD, Foclae1 and FocmedA(a) were found to be important regulators for pathogenicity and fusaric acid synthesis in Foc. The present study therefore advances our understanding of the regulation pathways of the asexual development and functional interdependence of sporulation-responsive genes in Foc.