Assessing Clade Specific Putative Secreted Proteins in Fusarium oxysporum f.sp vasinfectum for their Contribution to Virulence on Cotton

Abstract

Fusarium wilt (FW) of cotton is caused by the fungus Fusarium oxysporum f. sp. vasinfectum (Fov). Fov invades and colonizes the vascular system of cotton plants and results in browning or black discoloration of vascular bundles, wilting due to disrupted water transportation, and eventual plant death. Some of the virulence of Fov is mediated by effectors, which are usually small secreted proteins (SSPs). One of the roles of effectors is that they enable the pathogen to overcome the host defense system, e.g., pattern-triggered immunity, and to promote effector-triggered susceptibility to spread disease symptoms for the benefit of the pathogen. The main focus of this study is to evaluate clade specific secreted proteins in Fov race 4 that could be involved in virulence on cotton. In Chapter 2, using comparative genomics between twelve Fov genomes (cotton) and ten publicly available F. oxysporum genomes, host-specific putative secreted proteins which could be contributing to virulence (fungal effectors on cotton) were identified. Among the Fov isolates, the highly virulent race 4 is of particular interest due to its ability to cause early-season severe damage, including seedling wilt and death, without any nematode requirement to initiate infection. EffectorP3 was used to identify proteins that could serve as putative effectors, which identified eleven proteins specific to Fov race 4. To narrow down unique putative effectors, we conducted RT-qPCR to assess the relative expression levels of these genes during infection, identifying five putative secreted proteins of interest. Three mutants of SSP genes, FUN_011311, FUN_014580 and FUN_002905 were chosen for gene mutation based on their upregulation and presence as a single copy in the genome. A hydroponic virulence assay was conducted with Pima cotton cultivar Rowden, to assess whether these proteins serve as a virulence factor on cotton. FUN_011311 was confirmed to contribute to virulence on cotton. In conclusion, the Fov genomes can provide necessary resource for comparative genomic analysis to identify genes that are involved in pathogenicity on cotton and may be used to develop improved disease management strategies. Understanding the function of effectors in pathogen-plant interactions provides insight into the mechanisms of host specificity and pathogenicity, enabling the identification of genetic resistance markers and the development of resistant cotton varieties. Such foundational research is essential for devising innovative methods to combat pathogens like Fusarium, ultimately improving agricultural biosecurity and sustainability.