The Small Secreted Protein FoSsp1 Elicits Plant Defenses and Negatively Regulates Pathogenesis in Fusarium oxysporum f. sp. cubense (Foc4)

A Novel Effector FoUpe9 Enhances the Virulence of Fusarium oxysporum f. sp. cubense Tropical Race 4 by Inhibiting Plant Immunity

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is the most destructive disease of the banana. Effectors play a crucial role in Foc TR4-banana interaction; however, only a few effectors have been functionally characterized. Our previous secretome studies on Foc TR4 highlighted an uncharacterized protein without any conserved domains (named FoUpe9), which was predicted to be a candidate effector. Herein, bioinformatics analysis showed that FoUpe9 was highly conserved among Fusarium species. FoUpe9 was highly induced during the early infection stages in the banana. A yeast signal sequence trap assay showed that FoUpe9 is a secretory protein. FoUpe9 could inhibit cell death and ROS accumulation triggered by BAX through the Agrobacterium-mediated Nicotiana benthamiana expression system. Subcellular location showed that FoUpe9 was located in the nucleus and cytoplasm of N. benthamiana cells. Deletion of the FoUpe9 gene did not affect mycelial growth, conidiation, sensitivity to cell-wall integrity, or osmotic and oxidative stress, but significantly attenuated fungal virulence. FoUpe9 deletion diminished fungal colonization and induced ROS production and expression of SA-related defense genes in banana plants. These results suggest that FoUpe9 enhances Foc TR4 virulence by inhibiting host immune responses and provide new insights into the functions of the uncharacterized proteins, further enhancing our understanding of effector-mediated Foc TR4 pathogenesis.

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.

Proteomic insights into fruit-pathogen interactions: managing biotic stress in fruit

KEYMESSAGE

Proteomics has revealed complex immune responses in fruits, leading to the identification of potential disease biomarkers and resistance mechanisms. Fruit diseases caused by fungal and bacterial pathogens present critical challenges to global food security by reducing fruit shelf life and quality. This review explores the molecular dynamics of fruit-pathogen interactions using advanced proteomic techniques. These approaches include mass spectrometry-based identification, gel-based, and gel-free strategies, tailored to the unique compositions of fruit tissues for accurate protein extraction and identification. Proteomic studies reveal pathogen-induced changes in fruit proteomes, including the upregulation of defence-related proteins and suppression of metabolic pathways crucial for pathogen survival. Case studies on tomatoes, apples, and bananas highlight specific pathogen-responsive proteins, such as PR proteins and enzymes involved in ROS scavenging, which play roles in disease resistance mechanisms. The review further demonstrates the utility of proteomic data in identifying early disease biomarkers, guiding genetic improvements for disease resistance, and optimizing pathogen control measures. Integrating proteomic insights with transcriptomics and metabolomics provides a multidimensional understanding of fruit-pathogen interactions, paving the way for innovative solutions in agriculture. Future research should prioritize multi-omics approaches and field-level validations to translate laboratory findings into practical applications. The advancements discussed underscore the transformative role of proteomics in improving food security and sustainability amid challenges posed by climate change and increasing global food demand.

The Ubiquitous Wilt-Inducing Pathogen Fusarium oxysporum-A Review of Genes Studied with Mutant Analysis

Fusarium oxysporum is one of the most economically important plant fungal pathogens, causing devastating Fusarium wilt diseases on a diverse range of hosts, including many key crop plants. Consequently, F. oxysporum has been the subject of extensive research to help develop and improve crop protection strategies. The sequencing of the F. oxysporum genome 14 years ago has greatly accelerated the discovery and characterization of key genes contributing to F. oxysporum biology and virulence. In this review, we summarize important findings on the molecular mechanisms of F. oxysporum growth, reproduction, and virulence. In particular, we focus on genes studied through mutant analysis, covering genes involved in diverse processes such as metabolism, stress tolerance, sporulation, and pathogenicity, as well as the signaling pathways that regulate them. In doing so, we hope to present a comprehensive review of the molecular understanding of F. oxysporum that will aid the future study of this and related species.

The Verticillium dahliae Small Cysteine-Rich Protein VdSCP23 Manipulates Host Immunity

Verticillium wilt caused by Verticillium dahliae is a notorious soil-borne fungal disease and seriously threatens the yield of economic crops worldwide. During host infection, V. dahliae secretes many effectors that manipulate host immunity, among which small cysteine-rich proteins (SCPs) play an important role. However, the exact roles of many SCPs from V. dahliae are unknown and varied. In this study, we show that the small cysteine-rich protein VdSCP23 inhibits cell necrosis in Nicotiana benthamiana leaves, as well as the reactive oxygen species (ROS) burst, electrolyte leakage and the expression of defense-related genes. VdSCP23 is mainly localized in the plant cell plasma membrane and nucleus, but its inhibition of immune responses was independent of its nuclear localization. Site-directed mutagenesis and peptide truncation showed that the inhibition function of VdSCP23 was independent of cysteine residues but was dependent on the N-glycosylation sites and the integrity of VdSCP23 protein structure. Deletion of VdSCP23 did not affect the growth and development of mycelia or conidial production in V. dahliae. Unexpectedly, VdSCP23 deletion strains still maintained their virulence for N. benthamiana, Gossypium hirsutum and Arabidopsis thaliana seedlings. This study demonstrates an important role for VdSCP23 in the inhibition of plant immune responses; however, it is not required for normal growth or virulence in V. dahliae.

Loss of Phosphomannose Isomerase Impairs Growth, Perturbs Cell Wall Integrity, and Reduces Virulence of Fusarium oxysporum f. sp. cubense on Banana Plants

Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes Fusarium wilt of banana, necessitating urgent measures to control this disease. However, the molecular mechanisms underlying Foc TR4 virulence remain elusive. Phosphomannose isomerase is a key enzyme involved in the biosynthesis of GDP mannose, an important precursor of fungal cell walls. In this study, two phosphomannose isomerases were identified in the Foc TR4 genome, of which only Focpmi1 was highly expressed throughout all developmental stages. Generated null mutants in Foc TR4 showed that only the ΔFocpmi1 mutant required exogenous mannose for growth, indicating that Focpmi1 is the key enzyme involved in GDP mannose biosynthesis. The Focpmi1 deficient strain was unable to grow without exogenous mannose and exhibited impaired growth under stress conditions. The mutant had reduced chitin content in its cell wall, rendering it vulnerable to cell wall stresses. Transcriptomic analysis revealed up- and down-regulation of several genes involved in host cell wall degradation and physiological processes due to the loss of Focpmi1. Furthermore, Focpmi1 was also found to be crucial for Foc TR4 infection and virulence, making it a potential antifungal target to address the threats posed by Foc TR4.