Effector Profiles of Endophytic Fusarium Associated with Asymptomatic Banana (Musa sp.) Hosts.

Elizabeth Czislowski,Isabel Zeil-Rolfe,Elizabeth A B Aitken

doi:10.3390/ijms22052508

Elizabeth Czislowski, Isabel Zeil-Rolfe + Show 1 more

Open Access

https://doi.org/10.3390/ijms22052508

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Abstract

During the infection of a host, plant pathogenic fungi secrete small proteins called effectors, which then modulate the defence response of the host. In the Fusarium oxysporum species complex (FOSC), the secreted in xylem (SIX) gene effectors are important for host-specific pathogenicity, and are also useful markers for identifying the various host-specific lineages. While the presence and diversity of the SIX genes has been explored in many of the pathogenic lineages of F. oxysporum, there is a limited understanding of these genes in non-pathogenic, endophytic isolates of F. oxysporum. In this study, universal primers for each of the known SIX genes are designed and used to screen a panel of endophytically-associated Fusarium species isolated from healthy, asymptomatic banana tissue. SIX gene orthologues are identified in the majority of the Fusarium isolates screened in this study. Furthermore, the SIX gene profiles of these endophytic isolates do not overlap with the SIX genes present in the pathogenic lineages of F. oxysporum that are assessed in this study. SIX gene orthologues have not been commonly identified in Fusarium species outside of the FOSC nor in non-pathogenic isolates of F. oxysporum. The results of this study indicate that the SIX gene effectors may be more broadly distributed throughout the Fusarium genus than previously thought. This has important implications for understanding the evolution of pathogenicity in the FOSC.

Highlights

Species within the Fusarium genus represent some of the most devastating and important pathogens of many of the world’s agricultural crops
The ability of the universal primers to amplify their target secreted in xylem (SIX) gene was determined by screening isolates of F. oxysporum (n = 46) representing nine different formae speciales, whose SIX genes profiles could be investigated with whole-genome sequencing [22]
Plant pathogenic lineages of F. oxysporum, such as the banana pathogen Foc, represent a small fraction of the genetic diversity of the Fusarium oxysporum species complex (FOSC); many isolates exist in the rhizosphere as saprophytes whilst others can establish an endophytic, asymptomatic relationship with a host plant [2]

Summary

Introduction

Species within the Fusarium genus represent some of the most devastating and important pathogens of many of the world’s agricultural crops. The Fusarium oxysporum species complex (FOSC) includes isolates that can be pathogens, saprophytes and even endophytes [1,2]. The plant pathogenic lineages of F. oxysporum have been recorded to cause vascular wilt in over 100 species of plants [3,4,5]. An individual pathogenic isolate of F. oxysporum is a specialist and typically causes disease in only one or two host species. As a consequence of this host-specificity, isolates of F. oxysporum are classified into special groups called ‘formae speciales’ According to their specific host [1]. Many formae speciales consist of multiple, genetically distinct clonal lineages or vegetatively compatible groups (VCGs) [3,6,7]

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