Abstract
Phytophthora cinnamomi is a devastating pathogen causing root and crown rot and dieback diseases of nearly 5000 plant species. Accurate and rapid detection of P. cinnamomi plays a fundamental role within the current disease prevention and management programs. In this study, a novel effector gene PHYCI_587572 was found as unique to P. cinnamomi based on a comparative genomic analysis of 12 Phytophthora species. Its avirulence homolog protein 87 (Avh87) is characterized by the Arg-Xaa-Leu-Arg (RxLR) motif. Avh87 suppressed the pro-apoptotic protein BAX- and elicitin protein INF1-mediated cell death of Nicotiana benthamiana. Furthermore, a recombinase polymerase amplification-lateral flow dipstick detection assay targeting this P. cinnamomi-specific biomarker was developed. While successfully detected 19 P. cinnamomi isolates of a global distribution, this assay lacked detection of 37 other oomycete and fungal species, including P. parvispora, a sister taxon of P. cinnamomi. In addition, it detected P. cinnamomi from artificially inoculated leaves of Cedrus deodara. Moreover, the RPA-LFD assay was found to be more sensitive than a conventional PCR assay, by detecting as low as 2 pg of genomic DNA in a 50-µL reaction. It detected P. cinnamomi in 13 infested soil samples, while the detection rate was 46.2% using PCR. Results in this study indicated that PHYCI_587572 is a unique biomarker for detecting P. cinnamomi. Although PHYCI_587572 was identified as an effector gene based on the RxLR motif of Avh87 and the avirulence activity on Nicotiana, its exact genetic background and biological function on the natural hosts of P. cinnamomi warrant further investigations.
Highlights
Phytophthora cinnamomi is a destructive pathogen of nearly 5000 plant species including many economically important crops [1,2,3]
In the forests of south-west Western Australia, P. cinnamomi has permanently altered the composition of plant communities and caused drastic decline of biodiversity by killing over 3500 susceptible endemic plant species and threatening macrofungal and bird species [3,8,9,10]
PHYCI_587572, a potentially P. cinnamomi-specific RxLR effector gene identified using a comparative genomics approach, and a rapid and equipment-free Recombinase polymerase amplification (RPA)-LFD detection assay for P. cinnamomi that targets this novel biomarker
Summary
Phytophthora cinnamomi is a destructive pathogen of nearly 5000 plant species including many economically important crops [1,2,3]. Root rot caused by P. cinnamomi is a widely spread and most severe disease of avocado with an estimated annual loss of $40 million in California, USA. Phytophthora cinnamomi causes root and crown rot, canker and dieback diseases on a wide range of woody ornamental crops such as azalea, boxwood, camellia, cedar, and rhododendron [5]. In China, P. cinnamomi has been found in many provinces and municipalities such as Fujian [11,12,13], Hainan [14], Jiangsu [13], Shaanxi [15], Shanghai [16], and Zhejiang [13], threatening the production of avocado, blueberry, chestnut, kiwifruit, ornamental trees, and the health of natural forests
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