Understanding the Molecular Bases of the Endophytic/Pathogenic Behavior of Fusarium Oxysporum Interacting With Vanilla Planifolia

Members of the Fusarium oxysporum species complex (FOSC) has the capacity to specialize into host-specific pathogens known as formae speciales through horizontal gene transfer between pathogenic and endophytic individuals. To this day, the origin of these formae speciales and the genetic determinants dictating the switch from endophytic to pathogenic Fusarium oxysporum (Fox) are still unknown. F. oxysporum f. sp. vanillae (Fov), member of FOSC, is the causal agent of root and stem rot disease, representing the main phytosanitary problem in vanilla plantations worldwide. Here we analyzed the RNA-seq libraries resulting from the interaction vanilla-Fov at early and late stages of the infection, and what we initially identified as control in a previous study, detecting the presence of Fox endophytes. We identified virulence, hypervirulence, sporulation, conidiation, necrosis, and production of fusaric acid as key processes taking place during Fov-vanilla interaction. Through comparison with endophytic Fox, we found that Fov can infect vanilla thanks to the presence of pathogenicity islands and genomic regions associated with supernumerary chromosomes. These play a central role as carriers of genes involved with pathogenic activity and could have being obtained by Fov through horizontal gene transfer. We also found that, unlike other pathogenic members of FOSC, Fov do not use Secreted in Xylem proteins (SIX) to infect vanilla.

SIX6 Shows High Divergence in Fusarium oxysporum f. sp. cubense TR4

Secreted fungal effector proteins and their host targets are good examples to understand the mechanism of host-pathogen co-evolution with genes involved in the interaction undergoing positive selection. SIX genes (secreted in xylem) are obtained via horizontal transfer and can be found within the formae speciales of Fusarium oxysporum. SIX6 and SIX9 of F. oxysporum f. spp. cubense (Foc) are predicted to play a role as effectors. However, their involvement in the pathogenicity of Foc in banana plants has not been determined yet. In the susceptible banana cultivar, we found that the SIX6 and SIX9 genes of Foc TR4 were highly expressed in roots, but not in corms or leaves. The host, however, expressed the pathogenesis-related (PR) genes, PR-1 and PR-3, in corms earlier than in the roots. Phylogenetic analysis on SIX6 and SIX9 genes of F. oxysporum has revealed the separation of SIX6 and SIX9 of Foc from other formae speciales. This leads to detecting genes under positive selection using the ratio nonsynonymous to synonymous substitution rates (Ka/Ks). SIX6 of Foc showed an increase in diversity, but insufficient to drive positive selection. Conversely, SIX9 of Foc showed no divergence in the dN/dS ratio distribution, indicating purifying selection. © 2021 Friends Science Publishers

Secreted in Xylem Genes: Drivers of Host Adaptation in Fusarium oxysporum

Fusarium oxysporum (Fo) is a notorious pathogen that significantly contributes to yield losses in crops of high economic status. It is responsible for vascular wilt characterized by the browning of conductive tissue, wilting, and plant death. Individual strains of Fo are host specific (formae speciales), and approximately, 150 forms have been documented so far. The pathogen secretes small effector proteins in the xylem, termed as Secreted in Xylem (Six), that contribute to its virulence. Most of these proteins contain cysteine residues in even numbers. These proteins are encoded by SIX genes that reside on mobile pathogenicity chromosomes. So far, 14 proteins have been reported. However, formae speciales vary in SIX protein profile and their respective gene sequence. Thus, SIX genes have been employed as ideal markers for pathogen identification. Acquisition of SIX-encoding mobile pathogenicity chromosomes by non-pathogenic lines, through horizontal transfer, results in the evolution of new virulent lines. Recently, some SIX genes present on these pathogenicity chromosomes have been shown to be involved in defining variation in host specificity among formae speciales. Along these lines, the review entails the variability (formae speciales, races, and vegetative compatibility groups) and evolutionary relationships among members of F. oxysporum species complex (FOSC). It provides updated information on the diversity, structure, regulation, and (a)virulence functions of SIX genes. The improved understanding of roles of SIX in variability and virulence of Fo has significant implication in establishment of molecular framework and techniques for disease management. Finally, the review identifies the gaps in current knowledge and provides insights into potential research landscapes that can be explored to strengthen the understanding of functions of SIX genes.

The use of natural products against Fusarium oxysporum: A review

: Currently, numerous researchers have focused their attention on the use of natural products from plants and microorganisms, or compounds derived from these organisms to protect crops from various diseases, thus reduce the negative effects on human health and environmental safety. Fungal diseases cause a considerable loss of crop yields in agricultural industries worldwide. Fusarium oxysporum comprises a multitude of formae speciales that cause vascular wilt diseases of economically important crops. This review presents an overview of researches realized on natural products tested against Fusarium oxysporum formae speciales phytopathogens for the period (2017-2020). This review aims to collect major research works of the antifungal compounds against these fungi and up-dates information on their developments and approaches that have been rapidly taking place in recent years so that further novel researches can be envisaged. Discussion of these studies by analyzing different sources for antifusariosis treatment, evaluation of testing methods, and information on their advantages and limitations and to determine those with real efficacy. Despite the important number of natural products with remarkable in vitro efficiency, the limiting point is their in vivo application for soil microorganisms (in this case: Fusarium oxysporum). Therefore, more advanced researches are needed to solve this problem.

Identification of Pathogenicity Groups and Pathogenic Molecular Characterization of Fusarium oxysporum f. sp. sesami in China

Fusarium oxysporum f. sp. sesami is an extremely destructive pathogen, causing sesame Fusarium wilt disease worldwide. To clarify the pathogenicity and the genetic characters of F. oxysporum f. sp. sesami, we systematically investigated 69 F. oxysporum isolates collected from major sesame-growing areas in China. Among these isolates, 54 isolates were pathogenic and 15 were nonpathogenic according to pathogenicity testing on sesame seedlings. For the pathogenic isolates, three F. oxysporum f. sp. sesami pathogenicity groups were defined based on the three differential sesame hosts for the first time. A translation elongation factor 1α gene tree was constructed to determine the genetic diversity of the F. oxysporum isolates but could not separate F. oxysporum f. sp. sesami isolates from the nonpathogenic isolates and other F. oxysporum formae speciales. Ten secreted-in-xylem (SIX) genes (one family of effectors) were identified in F. oxysporum f. sp. sesami isolates by a search with the genome data, and were subsequently screened in the 69 F. oxysporum isolates. Compared with the SIX gene profiles in other F. oxysporum formae speciales, the presence and sequence variations of the SIX gene homologs directly correlated with the specific pathogenicity of F. oxysporum f. sp. sesami toward sesame. Furthermore, eight of these F. oxysporum f. sp. sesami SIX genes were significantly expressed in sesame plants as infection of the F. oxysporum f. sp. sesami isolate. These findings have important significance for understanding the pathogenic basis of F. oxysporum f. sp. sesami isolates, and will contribute to improve the diagnostics to effectively control Fusarium wilt disease in sesame.

MOLECULAR CHARACETIZATION OF TOMATO YELLOW LEAF CURL VIRUS AND FUSARIUM OXYSPORUM FORMAE SPECIALES AND RACES OF TOMATO AREAS IN NORTHERN CYPRUS

Fusarium oxysporum (FO) and viruses have caused wilt, root, crown rots, mosaic, yellowing and curling on tomato plants and have resulted economic yield losses on tomato production areas at Northern Cyprus (NC) in 2011–2015 years. Typical FO symptoms showing greenhouse and open field areas used for collecting 62 plants and suspected Tomato yellow leaf curl virus (TYLCV) of 76 tomato plants have been studied respectively. In the researches, four different primers (uni, sp 13, sp 23, sprl) were used to determine the formae speciales and races of 62 isolates of FO isolates from different locations. PCR analyse studies have revealed that 81% of collected samples were Fusarium oxysporum f.sp. lycopersici (FOL) and 19% of them were Fusarium oxysporum f.sp. radicis-lycopersici (FORL). Additionally, further PCR analyses have identified that 37% of FOL samples were race 1, 15% were race 2 and 29% were race 3 identified respectively. The different samples of 76 tomato plants were tested with specific primers in PCR amplifications. Their results determined that the strains TYLCV-Israel, TYLCV-Sicilia, TYLCV-Mild of TYLCV found. The molecular techniques have suggested that Israel, Sicilia and Mild strain of TYLCV were present in the tomato production areas at NC. The TYLCV races with single or mixed infections and Fusarium oxysporum formae speciales and races are able to identify in molecular techniques in not only accurately but also reliably.