Comparative genomics plays a role in the study of Verticillium species’ evolution, diversity, and pathogenicity. Analyzing the genomes of Verticillium species uncover genes and genetic elements essential for pathogenicity, host specificity and adaptation of the pathogen in different environments (Klosterman et al., 2011). A significant breakthrough in genomics occurred when scientists sequenced and annotated the genomes of Verticillium species such as V. dahliae and V. albo-atrum. Through comparative analysis of these genomes, researchers have discovered variations in genome size, gene content and gene expression patterns across these species, indicating distinct lifestyles and preferences for specific hosts (Klosterman et al., 2011). For example, V. dahliae has a larger genome compared to V. albo-atrum, which is enriched with genes encoding secretory proteins, carbohydrate processing as well as secondary metabolite biosynthesis. Overall, their research laid a robust groundwork for future studies, including functional analyses of polysaccharide lyases and genes located in lineage-specific regions. Comparative genomic studies have also provided insights into Verticillium species’ similarities and differences in virulence mechanisms. In-depth investigations have identified virulence factors specific to certain species; one example is the fujikurine biosynthesis gene clusters found exclusively within the genomes of V. dahliae and V. longisporum (Sayari et al., 2022). Furthermore, Ingram et al. (2020) compared the genomes of 18 tomato isolates of V. dahliae, revealing race features that contribute to host specificity and virulence. Their study identified seven effectors in highly variable genome regions, with race 2 resistance in tomatoes controlled by a single dominant locus, highlighting the need for modern genomics in breeding for durable resistance.

In another study, Depotter et al. (2019) investigated the genomic regions of V. dahliae that are related to its virulence, and they successfully identified effector genes that exhibit sequence conservation. Gleeson (2015) employed genomics to examine how V. dahliae interacts with cover crops and wild strawberries, focusing on host-pathogen interactions. This investigation discovered genes for virulence and host specificity, including those encoding effector proteins and enzymes that degrade cell walls. By utilizing a genome-based approach, Sayari et al. (2022) successfully analyzed PKS gene clusters in all available genomes of Verticillium species. Furthermore, in a recent publication, Arseneault et al. (2023) presented genome data from 192 V. dahliae isolates that infect potatoes across Canada. Their findings highlighted the diversity among V. dahliae strains originating from different regions in Canada. Comparative genomic studies have also revealed shared genes and pathways between Verticillium species and other fungal plant pathogens, such as Fusarium, Coletotrichum, and Botrytis, which are involved in producing phytotoxins carbohydrate-active enzymes as well as secreted proteins (Sayari et al., 2022; de Jonge et al., 2011).

In addition, the comparison genomics has shown how horizontal gene transfer influences the virulence of plant pathogens, with evidence that these pathogens acquired genes from other bacterial and fungal species (Shi-Kunne et al., 2019a,b). Comparative genomic research has also played an important role in understanding the relationships between Verticillium species and other fungal plant pathogens. For instance, Seidl et al. (2020) investigated repetitive elements and their impact on centromere diversity and evolution within the fungal genus Verticillium. This study provided insights into the epigenetic processes of centromere development among these fungi. Another study by Gibriel (2019) focused on the evolution of virulence in two Ascomycete plant pathogens, Zymoseptoria tritici and V. dahlia, shedding light on the underlying factors contributing to their pathogenicity. In another study, Fogelqvist et al. (2018) performed the genome analysis of V. longisporum. Their findings revealed regions of nonparental origin within its hybrid genome, suggesting that interspecific hybridization played a significant role in the evolution of V. longisporum.

Researchers have also identified genes and proteins associated with virulence and host specificity in V. dahliae, such as VdSsk2 and VdSte11. These genes are crucial for growth, virulence, and stress response (Yu et al., 2019). Comparative genomic studies have uncovered regions linked to hosts’ virulence and resistance. This valuable information assists us to have a much better understanding of the factors that contribute to the nature of these organisms (Harting et al., 2021; Li H. et al., 2020).

These comparative genomic studies have provided insights into the determinants of pathogenicity and identified potential targets for developing new strategies to combat verticillium wilt disease. For instance, Hu et al. (2014) studied the germination process of V. dahliae sclerotia using expression profiles, which revealed critical genetic mechanisms underlying this pathogen’s early stages of infection. Shi-Kunne et al. (2019a) employed computational prediction techniques to identify clusters of secondary metabolites in V. dahliae, suggesting their role in virulence and disease control. Chen et al. (2023) discovered sugar transporter genes that influence V. dahliae’s virulence on cotton plants, while Chavarro-Carrero et al. (2021) uncovered a particular Av2 effector protein recognized by tomato plants with a V2 resistance locus shedding light on plant-pathogen interactions. Effector proteins play crucial roles in determining the virulence of Verticillium species, making them an attractive target for developing methods to manage these diseases, such as making resilient cultivars or fungicides. Horizontal gene transfer events from bacterial species have also been suggested to play a role in acquiring effectors (Shi-Kunne et al., 2019a,b). In the coming section, we will discuss the role of horizontal gene transfer in verticillium pathogenicity.

Comparative genomics has revealed the evolutionary journey of Verticillium species. Depotter et al. (2021) reconstructed the phylogenetic relationships among 16 Verticillium species, uncovering speciation, hybridization and gene exchange. Genomic regions that undergo evolution may contribute to the pathogen adaptation to different hosts and environments. Harting et al. (2021) identified a region found exclusively in virulent V. longisporum isolates, which is crucial for their pathogenicity ability. Li X. et al. (2020) reported the sequences of V. dahliae strain XJ592 and non-deciduous strain XJ511, providing insights into the factors determining their pathogenicity ability. Zhang et al. (2021) shared genome sequence data for MAT1-1 and MAT1-2 idiomorphs of V. dahliae, enhancing our understanding of its evolution and adaptation.

Overall, comparative genomics is a powerful tool for understanding Verticillium species, revealing key aspects of their evolution and pathogenicity. This approach allows researchers to pinpoint specific genes and genetic elements linked to pathogenicity, host specificity, and adaptation. Moreover, by uncovering genetic similarities with other fungal pathogens, it broadens our understanding of fungal pathogenicity. As the field progresses, comparative genomics will continue to identify genetic determinants of virulence and adaptation, aiding in the development of effective disease control measures.

Population genomic studies have provided insights into Verticillium species’ diversity and population structure. In a study conducted by Zhang et al. (2019), the genome of V. dahliae was analyzed, and specific genomic regions associated with the defoliation phenotype were identified, indicating adaptation to host plants. Their research revealed that the defoliation and high virulence of the D pathotype are caused by the secondary metabolite NAE 12:0, whose biosynthesis is governed by genes within the lineage-specific region G-LSR2 in V. dahliae. Another study by Chen et al. (2021) focused on the V. dahliae race, revealing that host plants and management practices impact this pathogen’s population structure. They observed that different host plants were linked to subpopulations of V. dahliae, suggesting that host-specific adaptations play a vital role in the evolution of this important plant pathogen.

In an investigation carried out by Wang et al. (2021), the genetic basis behind the divergence of cultivars in V. dahliae was explored using comparative genomics, transcriptomics, and analysis of lineage-specific regions. Their findings indicated that cultivar divergence in V. dahliae was associated with acquiring effector genes important for interactions between hosts and pathogens. Similarly, Wheeler et al. (2019) examined endophyte populations within V. dahliae and highlighted changes in both genome and transcriptome associated with lifestyle alterations. Moreover, the study by Rafiei et al. (2018a) focused on analyzing the diversity and structure within subpopulations of V. dahliae from various hosts and regions, unveiling distinct patterns among them.

Overall, we have gained insights into the underlying molecular mechanisms behind host pathogen interactions in V. dahliae through population genomics. For instance, Wang et al. (2021) explored how different varieties of plants diverge and identified effector genes that play a crucial role in interactions between hosts and pathogens. Another research conducted by Fan et al. (2018) focused on understanding the toxicity of V. dahliae compatibility groups (VCGs) in strawberries, highlighting the influence of genetic factors on different compatibility groups (VCGs) virulence. Bautista-Jalón et al. (2021) examined the differences among populations of V. dahliae recovered from symptomatic and healthy-looking host plants using microsatellite markers. The findings revealed that populations from symptomatic plants exhibited higher genetic diversity and significant differentiation than those from asymptomatic plants. It is worth noting that different clonal lineages of V. dahliae may have developed diverse infection strategies over time, leading to variations in their virulence levels. In Fan et al. (2018) research, genome sequencing has assisted in uncovering differences across various regions of the genome and changes in potential effector genes among distinct isolates belonging to different VCGs within V. dahliea populations infecting strawberries, which indicates unique evolutionary approaches employed by this fungus when it comes to infection and affecting their overall virulence. The population structure and the gene flow among different Verticillium species significantly impact disease management strategies and contribute to the continuous evolution of these pathogens. According to a study conducted by Baroudy et al. (2019), genetic diversity exists in populations of V. dahliae found in olives and potatoes, impacting the presence of effector genes. Another study by Dung et al. (2019) analyzed V. dahliae populations isolated from mint and revealed relatively low genetic diversity, suggesting the potential for the evolution of pathogenic genotypes.

In general, population genomics has implications for disease management and agriculture as it influences factors such as pathogenicity, host range and resistance to fungicides. By understanding the structure of populations, we can develop strategies, like breeding for resistance and targeted use of fungicides. However, further research is necessary to assess their impact fully.

Horizontal gene transfer (HGT) which involves the exchange of material between organisms, play a crucial role in shaping diversity and aiding adaptation in Verticillium species. The movement of mobile genetic elements (MGE) such as plasmids, transposons, and bacteriophages within and between genomes significantly contributes to this process (Klosterman et al., 2011; Shi-Kunne et al., 2019a,b; Depotter et al., 2019; Zhang et al., 2022). These elements facilitate the transfer of genes between bacterial and fungal genomes, actively contributing to pathogen adaptation to environments (Torres et al., 2021; Faino et al., 2016). Many researchers have studied the impact of HGT and MGEs on Verticillium species using techniques such as transcriptomics and comparative genomics. For instance, Torres et al. (2021) identified transcripts derived from transposable elements (TEs) that influence gene expression regulation in this plant pathogen. They showed that TE dynamics in V. dahliae contribute to genomic variation, correlate with the expression of pathogenicity-related genes, and potentially influence the evolution of adaptive genomic regions.

Furthermore, TEs have been discovered to facilitate the transmission of virulence genes, promoting the development of pathogenic strains (McDonald et al., 2019). These mechanisms play an important role in adaptation and evolution as Verticillium species often undergo horizontal gene transfer events (Shi-Kunne et al., 2019a; Klosterman et al., 2011).

Horizontal gene transfer has been observed in Verticillium species, where they acquire genes from bacteria. This process enhances the fungus’s pathogenesis-related functions, including cell wall degradation and detoxification (Shi-Kunne et al., 2019a,b). In Verticillium genomes, the transfer of genes is also linked to the evolution of virulence. For instance, allelic variations in the V. dahliae Ave-1 effector gene and its presence in other fungal pathogens provide evidence of HGTs’ role (Chen et al., 2018). Furthermore, HGT can occur between bacteria and Verticillium as well as Verticillium with other fungal genera influencing the trajectory of pathogens (Chen et al., 2018). For instance, In V. longisporum, a lineage-specific genomic region associated with reduced virulence has been identified. HGT event with TEs as a mechanism is believed to be involved in this region’s evolution (Harting et al., 2021). Moreover, repetitive elements in the Verticillium genome, such as centromeres, contribute to diversity and evolution. These repetitive elements facilitate genetic material rearrangement between centromeres and aid adaptation to changing environmental conditions (Seidl et al., 2020).

Aside from HGT and MGE variations, chromosomal rearrangements in Verticillium, such as duplications, deletions, or transpositions, are linked to the gain and loss of virulence factors. These alterations impact the fungus’s ability to infect and colonize host plants and contribute to host specificity (de Jonge et al., 2013). The genome size reduction combined with rearrangement events has also been noted in different members of Verticillium, potentially influencing their ability to diversify and adapt to various host plants (Shi-Kunne et al., 2018).

Besides the nuclear genome, the mitochondrial genome of V. longisporum displays a mosaic structure due to allopolyploidization—a process involving duplication through hybridization between different species known as interspecific hybridization. This specific process is believed to have influenced V. Longisporum’s ability from infecting multiple crops to shift toward infecting mainly Brassicaceae plants. The mosaic structure of its genome was primarily caused by rearrangements between parental chromosomes, with gene conversion playing a minor role. The interaction between the mitochondrial and nuclear genomes played a significant role in maintaining genome stability and adapting V. longisporum to ecological niche (Depotter et al., 2018).

Understanding the mechanisms behind horizontal gene transfer, mobile genetic elements, and TEs in Verticillium genomes is vital for unraveling their diversity, pathogenicity, and ability to infect various hosts and survive in different environmental niches. These studies provide valuable information about the evolution of the genome in Verticillium. By gaining these insights, we can potentially develop strategies to combat plant diseases caused by Verticillium.

Transcriptomics is important in studying interactions between Verticillium fungi and host plants. It provides insights into the pathogenicity mechanisms of these important groups of fungi and how plants defend themselves against them. Researchers have used whole genome sequencing to identify genes that contribute to the virulence of V. dahliae and other Verticillium species and genes that determine their ability to infect specific hosts. By combining transcriptomics with genomics, Zhang et al. (2020) examined the expression of V. dahliae’s genes in cotton root exudates, uncovering pathogenicity and stress response genes. Similar approaches have been employed in studies involving tomato, cotton, and alfalfa (Medicago sativa), leading to discoveries and potential targets for disease control (Tan et al., 2015; Zhang et al., 2019; Li J. et al., 2022). A very recent transcriptome study by Zhang et al. (2023) explored the effects of mycosubtilin C17 and Chaetoviridine A on V. dahliae, revealing several functional pathways influenced by these antifungal compounds. Furthermore, recent advancements in transcriptomics have allowed for analysis of the dynamics of host-pathogen interactions.

To better understand the disease cycle of V. dahliae, researchers have employed different advanced methods such as genetics, transcriptomics and comparative analysis. Sarmiento-Villamil et al. (2020) employed inheritance genetics and transcriptomics to investigate the disease cycle of V. dahliae. Through their research, they identified three differentially expressed genes during infection, one of which was VdRGS1—a regulator involved in G protein signaling pathways. Deletion of VdRGS1 had impacts on the pathogen’s development and virulence, highlighting its role in disease progression. It was found that G protein-mediated signaling triggers the production of virulence factors during the biotrophic growth stages of V. dahliae, while inhibiting G protein signaling through VdRGS1 is necessary for microsclerotia production later in infection. Targeting the signaling of G proteins could present an approach for controlling diseases. However, additional research is required to develop such methods.

Several transcriptomic analyses have investigated how hosts respond to V. dahliae infection. For instance, Jiménez-Ruiz et al. (2019) examined the transcriptome of olive cultivars with varying levels of susceptibility, while Zhu et al. (2021b) analyzed a cotton variety that displayed increased resistance. On the other hand, Li et al. (2023) compared interspecific cotton lines to identify potential genes involved in verticillium wilt resistance. Comparative transcriptomic analyses have also unveiled networks and crucial genes associated with pathogenicity and host defense mechanisms. For example, Tan et al. (2015) delved into the interaction between tomatoes and V. dahliae, Guo et al. (2017) compared sunflower genes that respond to V. dahliae and Yang et al. (2019) examined transcriptional responses in eggplants. Additionally, Zhao et al. (2020) investigated cross-protection in sunflowers using a weakly aggressive strain of V. dahliae, Luo et al. (2019) used transcriptomics to study microsclerotia formation while Wang et al. (2021) analyzed the role of VdBre1 in cotton infection with V.dahliae. Moreover, Ramírez-Tejero et al. (2021) focused on olive roots’ basal gene expression for resistance against verticillium wilt and presented insights into understanding mechanisms involved in V.dahliae plant interactions.

RNA sequencing (RNA seq) is also used to investigate splicing in interactions between pathogens and their host plants. In a study by Jin et al. (2017), RNA seq was employed to analyze the transcriptomes of V. dahliae, revealing that over 50% of its multi-exon genes undergo alternative splicing. Targeting these splicing events might be possible to control infections caused by V. dahliae in crops. Similarly, Xiong et al. (2014) investigated microsclerotia development in V. dahliae and discovered that intron retention (RI) is involved in more than 95% of alternative splicing events. Jin et al. (2017, 2019) identified differentially expressed genes involved in alternative splicing regulation and virulence, shedding light on the importance of alternative splicing events and their role in fungal virulence. Additional investigation is required to understand the consequences of these events and their significance in the molecular mechanisms underlying microsclerotia development in V. dahliae.

In another study, Liu et al. (2022), using transcriptomics, identified VdCf2 as a regulator influencing growth, pathogenicity, and a gene cluster responsible for secondary metabolite production in V. dahliae. By controlling the expression of this gene cluster, VdCf2 impacts virulence and provides targets for antifungal drugs. Additionally, Liang et al. (2021) revealed the role of Nbnrp1 in defense responses triggered by the PevD1 effector from V. dahliae in Nicotiana benthamiana as a model organism. Nbnrp1 regulates sesquiterpenoid phytoalexin biosynthesis, inhibiting the growth of V. dahliae highlighting the importance of effector-triggered defense responses in plant immunity. Through examining the effector gene expression, Santhanam and Thomma (2013) investigated the role of Sge1. They found that it positively regulates some effector genes while repressing others—demonstrating the complex nature of effector gene regulation in V. dahliae.

Furthermore Zhang et al. (2020) examined how V. dahliae responds to cotton root exudates, establishing connections between this response and secondary metabolism as virulence. In another research, Tang et al. (2021) investigated the transcriptional variations in V. dahliae under different sources of inorganic nitrogen, whereas Wang et al. (2021) delved into understanding the importance of VdBre1 during cotton infection. In recent transcriptomic research, an unusual protein called VdTrx1 was identified, which is secreted and acts as a factor contributing to virulence as its deletion led to reduced pathogenicity (Tian et al., 2023). Another study by Zhang et al. (2020) shed light on the mechanisms underlying the interaction between V. dahliae and its host plant, providing insights into disease control strategies. These studies highlight the importance of transcriptome analysis in understanding Verticillium pathogenesis and host resistance, thus aiding in the development of effective control measures.

In the genomics era, proteomics has emerged as a crucial and powerful tool for understanding the complexities of Verticillium pathogenesis. Proteomic analysis offers a view of the events that shape the dynamics between hosts and pathogens by investigating protein expression, interactions, modifications, and functions during infection. Hu et al. (2019) conducted proteome and metabolome analyses to explore the interaction between tomatoes and V. dahliae, uncovering changes in defense-related proteins. In a study, Zhang et al. (2019) utilized phosphor proteomics to examine how cotton roots respond to V. dahliae, identifying phosphorylated proteins involved in defense and signaling pathways. Besides enhancing our understanding of host responses, phosphor proteomics provides information on targets for modifying these pathways to improve disease resistance.

Exo proteomics has also played an essential role in identifying pathogenicity factors within V. dahliae. This method offers insights into the proteins that contribute to the pathogen’s virulence ability. Such knowledge is crucial for developing targeted interventions that disrupt these pathogenicity factors and pave the way for strategies for preventing infections. Recent research conducted by Tian et al. (2023) identified Thoredox VdTrx1 as a factor that decreases the host’s immunity, thus contributing to the virulence of Verticillium. The discovery of Thoredox VdTrx1 in Verticillium as a virulence factor adds to the puzzle shedding light on the intricate molecular strategies Verticillium uses to establish infections. This protein’s discovery has been opening avenues for further research and potential interventions aimed at disease control.

Effector proteins also play a crucial role in Verticillium pathogenesis, as explained by de Sain and Rep (2015). These proteins unpredictably alter host pathways and cell structures. For example, the discovery of XFORCE1 revealed its targeting of plant mRNA turnover and its ability to induce changes in cell identity (Subieta, 2023). Such examples highlight the various ways effectors undermine host defenses. Additionally, an effector found in V. dahliae that influences tomato pathogenicity through its interaction with auxin response factors provides evidence of the interplay between this microbe and its host (Li F. et al., 2022).

In conclusion, the studies mentioned above collectively emphasize proteomics’ role in understanding the molecular mechanisms involved in Verticillium pathogenesis. The intricate concept of the information derived from studies enhances our understanding of Verticillium host interactions and provides a new opportunity for developing targeted approaches to control diseases. As we delve deeper into the proteomics realm, it becomes necessary to conduct further research to unravel the complex network of molecular events, identify new effectors, and explore potential targets for mitigating the impact of verticillium wilt in agriculture.

The advent of high throughput sequencing techniques as well as the availability of reference genomes have presented the new era, in unraveling the genetic foundations of plant disease resistance through genome wide association studies (GWAS) (Song et al., 2020). In the case of Verticillium, GWAS has emerged as a tool for identifying genes and pathways associated with resistance across different plant species. For instance, Cotton was the subject of a GWAS study where the scientists uncovered genes that are associated with Verticillium resistance (Li et al., 2017). Following studies focused on Gossypium arboreum (Gong et al., 2018) and G. barbadense (Li et al., 2018) expanded upon this idea improving our understanding of factors related to resistance in cotton cultivars. Remarkably, an inclusive GWAS analysis conducted to identify quantitative trait loci (QTL) associated with resistance against both Verticillium and fusarium race 4 in upland cotton (Abdelraheem et al., 2020). The discovery of QTLs holds promise for developing cotton cultivars with enhanced resistance against Verticillium through marker assisted breeding.

The broad application of GWAS enables researchers to identify factors that confer resistance in plant species offering a more extensive perspective on the mechanisms underlying Verticillium resistance. For example, GWAS was also employed in autotetraploid alfalfa (Medicago sativa L.) to discover markers, for verticillium wilt resistance (Li et al., 2018). This represents a big step, in the development of strategies to breed alfalfa cultivars with increased resistance to Verticillium. Furthermore, GWAS, QTL seq and transcriptome sequencing techniques were employed to identify candidate genes and develop markers for breeding Verticillium varieties (Zhao et al., 2021). Their work showcased the integration of different cutting-edge approaches for a more comprehensive understanding of Verticillium-host interactions. In a recent study, Fartash et al. (2023) pinpointed loci associated with quantitative resistance in Medicago truncatula to V. Alfalfae thereby contributing to enhanced resistance.

Apart from identifying genetic factors GWAS has also played a vital role in unraveling the intricate molecular aspects of Verticillium pathogenesis. For example, Zhou et al. (2023) investigated heat shock protein genes in cotton, revealed their response to biotic stress and infection caused by V. dahliae. This highlights how GWAS can uncover not just resistance related genes but also provide insights into the mechanisms involved in host pathogen interactions.

In general, GWAS remains a strong methodology for discovery of the genetic factors associated with Verticillium wilt resistance. The studies mentioned above provide a path, for the development of resilient plant cultivars and the enhancement of strategies to control diseases caused by different Verticillium species. As we continue to advance our knowledge about the factors behind plant resistance, it is likely that GWAS will play a role in determining the future of crop breeding and contributing to worldwide initiatives aimed at minimizing the negative effects of Verticillium wilt, on agricultural productivity.

Genetic modification is a great technique to better understand the factors contributing to the pathogenicity and virulence of plant pathogens. The ability to introduce foreign DNA into V. dahliae’s genome has greatly aided in studying the genes for its virulence and pathogenicity (Rehman et al., 2016). Comparative studies on the genome of V. dahliae have revealed diversity and rearrangement within its chromosomes highlighting the importance of comprehending its genetic composition (de Jonge et al., 2013). Moreover, as explained earlier, by examining assemblies of V. dahliae researchers have identified genomic regions that are highly flexible and enriched with TEs, duplicated genes, as well as genes involved in signaling and transcriptional regulation which provide valuable insights for potential genetic modification studies (Klosterman et al., 2011). The emphasis on resistance to combat Verticillium wilt diseases underscores the significance of using genetic modification techniques to unravel mechanisms related to resistance and pathogenicity (Santhanam et al., 2017). It is widely acknowledged that genetic transformation serves as a platform for exploring gene function in V. dahliae enabling us to uncover information about its virulence and pathogenicity at a genetic level (Rehman et al., 2016). Therefore, genetic transformation plays a role in unraveling the underlying genetics behind pathogenicity, host interactions and identifying strategies, for disease control. In this section we will explore research on Verticillium focusing on significant methods of transformation that have been utilized.