Transformation of Fusarium oxysporum by particle bombardment and characterisation of the resulting transformants expressing a GFP transgene

Generation of Epichloë Strains Expressing Fluorescent Proteins Suitable for Studying Host-Endophyte Interactions and Characterisation of a T-DNA Integration Event

Methods for the identification and localisation of endophytic fungi are required to study the establishment, development, and progression of host-symbiont interactions, as visible reactions or disease symptoms are generally absent from host plants. Fluorescent proteins have proved valuable as reporter gene products, allowing non-invasive detection in living cells. This study reports the introduction of genes for two fluorescent proteins, green fluorescent protein (GFP) and red fluorescent protein, DsRed, into the genomes of two distinct perennial ryegrass (Lolium perenne L.)-associated Epichloë endophyte strains using A. tumefaciens-mediated transformation. Comprehensive characterisation of reporter gene-containing endophyte strains was performed using molecular genetic, phenotypic, and bioinformatic tools. A combination of long read and short read sequencing of a selected transformant identified a single complex T-DNA insert of 35,530 bp containing multiple T-DNAs linked together. This approach allowed for comprehensive characterisation of T-DNA integration to single-base resolution, while revealing the unanticipated nature of T-DNA integration in the transformant analysed. These reporter gene endophyte strains were able to establish and maintain stable symbiotum with the host. In addition, the same endophyte strain labelled with two different fluorescent proteins were able to cohabit the same plant. This knowledge can be used to provide the basis to develop strategies to gain new insights into the host-endophyte interaction through independent and simultaneous monitoring in planta throughout its life cycle in greater detail.

Genetic manipulation of Fonsecaea pedrosoi using particles bombardment and Agrobacterium mediated transformation

Fonsecaea pedrosoi, a melanized fungal pathogen that causes Chromoblastomycosis, a human disease with a worldwide distribution. Biolistic is a widely used technique for direct delivery of genetic material into intact cells by particles bombardment. Another well-established transformation method is Agrobacterium-mediated transformation (ATMT), which involves the transfer of a T-DNA from the bacterium to the target cells. In F. pedrosoi there are no reports of established protocols for genetic transformation, which require optimization of physical and biological parameters. In this work, intact conidia of F. pedrosoi were particle bombarded and subjected to ATMT. In addition, we proposed hygromycin B, nourseothricin and neomycin as dominant selective markers for F. pedrosoi and vectors were constructed. We tested two parameters for biolistic: the distance of the particles to the target cells and time of cells recovery in nonselective medium. The biolistic efficiency was 37 transformants/μg of pFpHYG, and 45 transformants/μg of pAN7.1. Transformants expressing GFP were successfully obtained by biolistic. A co-culture ratio of 10: 1 (bacterium: conidia) and co-incubation time of 72 h yielded the largest number of transformants after ATMT. Southern blot analysis showed the number of foreign DNA insertion into the genome is dependent upon the plasmid used to generate the mutants. This work describes for the first time two efficient methods for genetic modification of Fonsecaea and these results open new avenues to better understand the biology and pathogenicity of the main causal agent of this neglected disease.

Dynamics of Colonization and Expression of Pathogenicity Related Genes in Fusarium oxysporum f.sp. ciceri during Chickpea Vascular Wilt Disease Progression

Fusarium wilt caused by Fusarium oxysporum f.sp. ciceri (Foc) is a constant threat to chickpea productivity in several parts of the world. Understanding the molecular basis of chickpea-Foc interaction is necessary to improve chickpea resistance to Foc and thereby the productivity of chickpea. We transformed Foc race 2 using green fluorescent protein (GFP) gene and used it to characterize pathogen progression and colonization in wilt-susceptible (JG62) and wilt-resistant (Digvijay) chickpea cultivars using confocal microscopy. We also employed quantitative PCR (qPCR) to estimate the pathogen load and progression across various tissues of both the chickpea cultivars during the course of the disease. Additionally, the expression of several candidate pathogen virulence genes was analyzed using quantitative reverse transcriptase PCR (qRT-PCR), which showed their characteristic expression in wilt-susceptible and resistant chickpea cultivars. Our results suggest that the pathogen colonizes the susceptible cultivar defeating its defense; however, albeit its entry in the resistant plant, further proliferation is severely restricted providing an evidence of efficient defense mechanism in the resistant chickpea cultivar.

Host perception of jasmonates promotes infection by Fusarium oxysporum formae speciales that produce isoleucine- and leucine-conjugated jasmonates

Three pathogenic forms, or formae speciales (f. spp.), of Fusarium oxysporum infect the roots of Arabidopsis thaliana below ground, instigating symptoms of wilt disease in leaves above ground. In previous reports, Arabidopsis mutants that are deficient in the biosynthesis of abscisic acid or salicylic acid or insensitive to ethylene or jasmonates exhibited either more or less wilt disease, than the wild-type, implicating the involvement of hormones in the normal host response to F. oxysporum. Our analysis of hormone-related mutants finds no evidence that endogenous hormones contribute to infection in roots. Mutants that are deficient in abscisic acid and insensitive to ethylene show no less infection than the wild-type, although they exhibit less disease. Whether a mutant that is insensitive to jasmonates affects infection depends on which forma specialis (f. sp.) is infecting the roots. Insensitivity to jasmonates suppresses infection by F. oxysporum f. sp. conglutinans and F. oxysporum f. sp. matthioli, which produce isoleucine- and leucine-conjugated jasmonate (JA-Ile/Leu), respectively, in culture filtrates, whereas insensitivity to jasmonates has no effect on infection by F. oxysporum f. sp. raphani, which produces no detectable JA-Ile/Leu. Furthermore, insensitivity to jasmonates has no effect on wilt disease of tomato, and the tomato pathogen F. oxysporum f. sp. lycopersici produces no detectable jasmonates. Thus, some, but not all, F. oxysporum pathogens appear to utilize jasmonates as effectors, promoting infection in roots and/or the development of symptoms in shoots. Only when the infection of roots is promoted by jasmonates is wilt disease enhanced in a mutant deficient in salicylic acid biosynthesis.

Transformation of Metarhizium anisopliae with benomyl resistance and green fluorescent protein genes provides a tag for genetically engineered strains

A plasmid, pBGFP, carrying green fluorescent protein (gfp) and benomyl-resistance genes was constructed and transformed into Metarhizium anisopliae. The transformants grew normally and GFP fluorescence was detected. No change was found in virulence for the transformants. Fluorescence was detected in hyphae from the haemolymph of the infected locust, and the benomyl-resistance was maintained. Results suggested that the two markers provided a useful tool for screening and monitoring the engineered strains even after infection.