Abstract
Forests are under threat from pests, pathogens, and changing climate. A major forest pathogen worldwide is the hemibiotroph Dothistroma septosporum, which causes dothistroma needle blight (DNB) of pines. While D. septosporum uses effector proteins to facilitate host infection, it is currently unclear whether any of these effectors are recognised by immune receptors to activate the host immune system. Such information is needed to identify and select disease resistance against D. septosporum in pines. We predicted and investigated apoplastic D. septosporum candidate effectors (DsCEs) using bioinformatics and plant-based experiments. We discovered DsCEs that trigger cell death in the angiosperm Nicotiana spp., indicative of a hypersensitive defence response and suggesting their recognition by immune receptors in non-host plants. In a first for foliar forest pathogens, we developed a novel protein infiltration method to show that tissue-cultured pine shoots can respond with a cell death response to a DsCE, as well as to a reference cell death-inducing protein. The conservation of responses across plant taxa suggests that knowledge of pathogen–angiosperm interactions may also be relevant to pathogen–gymnosperm interactions. These results contribute to our understanding of forest pathogens and may ultimately provide clues to disease immunity in both commercial and natural forests.
Highlights
Forests are under threat from pests, pathogens, and changing climate
The D. septosporum genome has approximately 12,580 predicted genes, 397 of which encode putatively secreted proteins that are expressed during infection of P. radiata seedlings[20,27,38]
Screening with pathogen effectors based on genome data has fast-tracked identification of resistant angiosperm crop varieties with corresponding immune receptors, it is not known whether a similar effectoromics-based approach could be applied to improve forest health given the longer life-cycles of forest trees, and the complexity of factors affecting disease resistance[36]
Summary
Forests are under threat from pests, pathogens, and changing climate. A major forest pathogen worldwide is the hemibiotroph Dothistroma septosporum, which causes dothistroma needle blight (DNB) of pines. Collectively called invasion patterns (IPs), to activate the plant’s innate immune s ystem[13] Following recognition by these PRRs, a series of immune responses of varying intensity are triggered, the strongest of which is the hypersensitive response (HR)[14], which involves localised cell death and a burst of reactive oxygen species (ROS) that quickly halt the invading pathogen’s growth. Given this hostility, successful pathogens must neutralise the apoplastic environment to colonise their hosts and cause disease
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