Taxonomy: Kingdom Fungi; Phylum Ascomycota; Class Sordariomycetes; Order Hypocreales; Family Nectriaceae; genus Fusarium. Host range: Very broad at the species level. More than 120 different formae speciales have been identified based on specificity to host species belonging to a wide range of plant families. Disease symptoms: Initial symptoms of vascular wilt include vein clearing and leaf epinasty, followed by stunting, yellowing of the lower leaves, progressive wilting, defoliation and, finally, death of the plant. On fungal colonization, the vascular tissue turns brown, which is clearly visible in cross-sections of the stem. Some formae speciales are not primarily vascular pathogens, but cause foot and root rot or bulb rot. Economic importance: Can cause severe losses in many vegetables and flowers, field crops, such as cotton, and plantation crops, such as banana, date palm and oil palm. Control: Use of resistant varieties is the only practical measure for controlling the disease in the field. In glasshouses, soil sterilization can be performed. Useful websites: http://www.broad.mit.edu/annotation/genome/fusarium_group/MultiHome.html; http://www.fgsc.net/Fusarium/fushome.htm; http://www.phi-base.org/query.php

Pathogen profile update: Fusarium oxysporum

Plant resistance to pathogens relies on a complex network of constitutive and inducible defensive barriers. The plant cell wall is one of the barriers that pathogens need to overcome to successfully colonize plant tissues. The traditional view of the plant cell wall as a passive barrier has evolved to a concept that considers the wall as a dynamic structure that regulates both constitutive and inducible defense mechanisms, and as a source of signaling molecules that trigger immune responses. The secondary cell walls of plants also represent a carbon-neutral feedstock (lignocellulosic biomass) for the production of biofuels and biomaterials. Therefore, engineering plants with improved secondary cell wall characteristics is an interesting strategy to ease the processing of lignocellulosic biomass in the biorefinery. However, modification of the integrity of the cell wall by impairment of proteins required for its biosynthesis or remodeling may impact the plants resistance to pathogens. This review summarizes our understanding of the role of the plant cell wall in pathogen resistance with a focus on the contribution of lignin to this biological process.

https://biblio.ugent.be/publication/5866457/file/5866474.pdf

The role of the secondary cell wall in plant resistance to pathogens

Jasmonate signaling plays an important role in both plant defense and development. Here, we have identified a subunit of the Mediator complex as a regulator of the jasmonate signaling pathway in Arabidopsis thaliana. The Mediator complex is a conserved multiprotein complex that acts as a universal adaptor between transcription factors and the RNA polymerase II transcriptional machinery. We report that the PHYTOCHROME AND FLOWERING TIME1 (PFT1) gene, which encodes the MEDIATOR25 subunit of Mediator, is required for jasmonate-dependent defense gene expression and resistance to leaf-infecting necrotrophic fungal pathogens. Conversely, PFT1 appears to confer susceptibility to Fusarium oxysporum, a root-infecting hemibiotrophic fungal pathogen known to hijack jasmonate responses for disease development. Consistent with this, jasmonate gene expression was suppressed in the pft1 mutant during infection with F. oxysporum. In addition, a wheat (Triticum aestivum) homolog of PFT1 complemented the defense and the developmental phenotypes of the pft1 mutant, suggesting that the jasmonate signaling functions of PFT1 may be conserved in higher plants. Overall, our results identify an important control point in the regulation of the jasmonate signaling pathway within the transcriptional machinery.

The Mediator Complex Subunit PFT1 Is a Key Regulator of Jasmonate-Dependent Defense in Arabidopsis

Salicylic acid-induced resistance to Fusarium oxysporum f. sp. lycopersici in tomato.

Virus Diseases of Peanut

Methyl jasmonate induced gene expression in wheat delays symptom development by the crown rot pathogen Fusarium pseudograminearum

Fusarium oxysporum is a soilborne fungal pathogen that causes major economic losses by inducing necrosis and wilting symptoms in many crop plants In this study, the interaction between F oxysporum and the model plant Arabidopsis thaliana has been investigated to better understand the nature of host defences that are effective against the Fusarium wilt pathogen The expression of salicylate- and jasmonate-responsive defence genes in F oxysporum-challenged roots of A thaliana plants as well as in the roots of plants whose leaves were treated with salicylate or jasmonate was analysed Unexpectedly, genes (eg PR1, PDF12, and CHIB) encoding proteins with defensive functions or transcription factors (eg ERF1, AtERF2, AtERF4 and AtMYC2) known to positively or negatively regulate defences against F oxysporum were not activated in F oxysporum-inoculated roots In contrast, the jasmonate-responsive defence gene PDF12 was induced in the leaves of plants whose roots were challenged with F oxysporum, but the salicylate-responsive PR1 gene was not induced in the leaves of inoculated plants Exogenous salicylic acid treatment prior to inoculation, however, activated PR1 and BGL2 defence gene expression in leaves and provided increased F oxysporum resistance as evidenced by reduced foliar necrosis and plant death Exogenous salicylic acid treatment of the foliar tissue did not activate defence gene expression in the roots of plants This suggests that salicylate-dependent defences may function in foliar tissue to reduce the development of pathogen-induced wilting and necrosis Despite the induction of defence gene expression in the leaves by jasmonate, this treatment did not lead to increased resistance to F oxysporum Overall, the results presented here suggest that the genetic manipulation of plant defence signalling pathways is a useful strategy to provide increased Fusarium wilt resistance

Salicylic acid mediates resistance to the vascular wilt pathogen Fusarium oxysporum in the model host Arabidopsis thaliana

Constitutive expression of a phenylalanine ammonia-lyase gene from Stylosanthes humilis in transgenic tobacco leads to enhanced disease resistance but impaired plant growth

The novel antimicrobial peptide MiAMP1, originally isolated from the seeds of Macadamia integrifolia, was constitutively expressed in transgenic tobacco and canola plants to test its effect on disease resistance. Analysis of plants transformed with 35S-MiAMP1 construct by northern and western blot analyses demonstrated the presence of MiAMP1 mRNA and the mature peptide in the transgenic plants. The MiAMP1 purified from the leaves of transgenic plants was biologically active with the same in vitro antifungal activity as native MiAMP1 purified from the seeds of macadamia. The effect of MiAMP1 expression on the economically important canola pathogen Leptosphaeria maculans (causal agent of blackleg disease) was evaluated in comparison with an untransformed control line and an azygous segregant derived from one of the transgenic lines. Lesion development on the cotyledons of the inoculated canola seedlings was significantly reduced in the T-2 progeny of seven independently transformed transgenic lines. These results suggested that, transgenic canola expressing MiAMP1 may be useful for the management of blackleg disease.

Kemal Kazan

Papers

Methyl jasmonate induced gene expression in wheat delays symptom development by the crown rot pathogen Fusarium pseudograminearum

Salicylic acid mediates resistance to the vascular wilt pathogen Fusarium oxysporum in the model host Arabidopsis thaliana

Constitutive expression of a phenylalanine ammonia-lyase gene from Stylosanthes humilis in transgenic tobacco leads to enhanced disease resistance but impaired plant growth

Enhanced quantitative resistance to Leptosphaeria maculans conferred by expression of a novel antimicrobial peptide in canola (Brassica napus L.)

Transcription factor genes controlling plant defence