Abstract
Phytophthora cinnamomi is a destructive pathogen causing root rot and dieback diseases on hundreds of economically and ecologically important plant species. Effective transformation systems enable modifications of candidate genes to understand the pathogenesis of P. cinnamomi. A previous study reported a polyethylene glycol and calcium dichloride (PEG/CaCl2)-mediated protoplast transformation method of P. cinnamomi. However, the virulence of the transformants was compromised. In this study, we selected ATCC 15400 as a suitable wild-type isolate for PEG/CaCl2 transformation using the green fluorescent protein after screening 11 P. cinnamomi isolates. Three transformants, namely, PcGFP-1, PcGFP-3, and PcGFP-5, consistently displayed a green fluorescence in their hyphae, chlamydospores, and sporangia. The randomly selected transformant PcGFP-1 was as virulent as the wild-type isolate in causing hypocotyl lesions on lupines. Fluorescent hyphae and haustoria were observed intracellularly and intercellularly in lupine tissues inoculated with PcGFP-1 zoospores. The potential application of this improved transformation system for functional genomics studies of P. cinnamomi is discussed.
Highlights
The genus Phytophthora contains over 100 plant pathogenic species that severely threaten agricultural production and natural ecosystems (Erwin and Ribeiro, 1996; Lamour et al, 2007; Kamoun et al, 2015), such as Phytophthora infestans causing late blight of potato (Fry and Goodwin, 1997), Phytophthora sojae causing root and stem rot of soybean (Schmitthenner, 1985), Phytophthora ramorum causing sudden oak death (Rizzo et al, 2002), Phytophthora capsici causing Phytophthora blight of many vegetable crops (Hausbeck and Lamour, 2004), and Phytophthora cinnamomi
Understanding the pathogenesis of P. cinnamomi is the key to the successful management of Phytophthora root rot and dieback
This study reports the first transformation of P. cinnamomi that successfully produced transformants with wild-type levels of vegetative growth and virulence (Figure 7)
Summary
The genus Phytophthora contains over 100 plant pathogenic species that severely threaten agricultural production and natural ecosystems (Erwin and Ribeiro, 1996; Lamour et al, 2007; Kamoun et al, 2015), such as Phytophthora infestans causing late blight of potato (Fry and Goodwin, 1997), Phytophthora sojae causing root and stem rot of soybean (Schmitthenner, 1985), Phytophthora ramorum causing sudden oak death (Rizzo et al, 2002), Phytophthora capsici causing Phytophthora blight of many vegetable crops (Hausbeck and Lamour, 2004), and Phytophthora cinnamomi. P. cinnamomi, a devastating plant pathogen causing Phytophthora root rot and dieback diseases, has a global distribution and a large host range The diseases caused by P. cinnamomi can lead to enormous losses in agriculture and forestry and a reduction in biodiversity (Hardham and Blackman, 2018). The identification of pathogenesis-related (PR) genes of P. cinnamomi has been rapidly advanced by the improvement of genome sequencing and bioinformatics technologies. A repository of PR genes of P. cinnamomi has been identified, the functions of the vast majority of these genes have not been determined (Hardham and Blackman, 2018; Dai et al, 2020). The central approach to this endeavor is applying transformation technologies to obtain the mutants of the studied PR genes
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