Successful Agrobacterium mediated transformation of Thielaviopsis basicola by optimizing multiple conditions

Thyrostroma carpophilum insertional mutagenesis: A step towards understanding its pathogenicity mechanism

Thyrostroma carpophilum, a causal agent of shot hole disease of stone fruits, cause severe loss in economically important fruit crops of Kashmir. Understanding its pathogenesis at molecular level will aid in devising a better management strategy. In this study, we optimized Agrobacterium tumefaciens mediated transformation (ATMT) conditions for T. carpophilum using PBIF2-EGFP construct. Using this protocol, we obtained 328 positive transformants per 10⁴ spores and subsequent sub-culturing of transformants on selective and non-selective media resulted in stable T-DNA integration. Southern blot analysis revealed that most of the transformants embodied single T-DNA integration. Using this method, we obtained a small-scale transformant library (2050 transformants). Among this pool, we tested 1005 transformants for their pathogenicity; out of which 185 showed complete pathogenicity loss, 35 displayed reduced virulence and 785 were pathogenically similar to wild type. Out of this experimental stock, three transformants from each category were randomly selected to dissect the infection assay. The findings deciphered that transformants with complete pathogenicity loss failed to penetrate the host tissue and a few transformants failed to sporulate in laboratory. Transformants from reduced category could not form appressorium and occasionally sporulated. Transformants similar to wild type were morphologically and pathogenically similar to wild type because of un-alteration in their modus operandi. Our work provides a new platform to understand the pathogenicity mechanism of T. carpophilum. The optimized ATMT protocol will help in developing large transformant library that can help to identify the virulence arsenals necessary for the pathogen to cause disease.

Agrobacterium-mediated transformation of Ceratocystis albifundus

Functional association between genomic loci and specific biological traits remains lacking in many fungi, including the African tree pathogen Ceratocystis albifundus. This is mainly because of the absence of suitable transformation systems for allowing genetic manipulation of this and other fungi. Here, we present an optimized protocol for Agrobacterium tumefaciens-mediated transformation of C. albifundus. Strain AGL-1 of A. tumefaciens and four binary T-DNA vectors (conferring hygromycin B or geneticin resistance and/or expressing the green fluorescent protein [GFP]) were used for transforming germinated conidia of three isolates of C. albifundus. Stable expression of these T-DNA-encoded traits was confirmed through sequential sub-culturing of fungal transformants on selective and non-selective media and by using PCR and sequence analysis. Single-copy integration of the respective T-DNAs into the genomes of these fungi was confirmed using Southern hybridization analysis. The range of experimental parameters determined and optimised included: (i) concentrations of hygromycin B and geneticin required for inhibiting growth of the wild type fungus and (ii) the dependence of transformation on acetosyringone for inducing the bacterium's virulence genes, as well as (iii) the duration of fungus-bacterium co-cultivation periods and (iv) the concentrations of fungal conidia and bacterial cells used for the latter. The system developed in this study is stable with a high-efficiency, yielding up to 400 transformants per 10⁶ conidia. This is the first report of a transformation protocol for C. albifundus and its availability will be invaluable for functional studies in this important fungus.