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Expression of BvGLP-1 Encoding a Germin-Like Protein from Sugar Beet in Arabidopsis thaliana Leads to Resistance Against Phytopathogenic Fungi

¹Department of Molecular Phytopathology, Institute of Phytopathology Christian-Albrechts-University of Kiel, Hermann-Rodewald Str. 9, D-24118 Kiel, Germany; ²Institute of Plant Physiology, Friedrich-Schiller-University Jena, Dornburger Str. 159, D-07743 Jena, Germany; ³Institute of Botany, Christian-Albrechts-University of Kiel, Olshausenstr. 40, D-24118 Kiel, Germany; ⁴Institute of Phytopathology, Zhejiang University, Hangzhou 310029, China

Nematode (Heterodera schachtii) resistance in sugar beet (Beta vulgaris) is controlled by a single dominant resistance gene, Hs1^pro-1. BvGLP-1 was cloned from resistant sugar beet. The BvGLP-1 messenger (m)RNA is highly upregulated in the resistant plants after nematode infection, suggesting its role in the Hs1^pro-1 mediated resistance. BvGLP-1 exhibits sequence homology to a set of plant germin-like proteins (GLP), from which several have proved to be functional in plant basal or defense resistance against fungal pathogens. To test whether BvGLP-1 is also involved in the plant--fungus interaction, we transferred BvGLP-1 into Arabidopsis and challenged the transgenic plants with the pathogenic fungi Verticillium longisporum and Rhizoctonia solani as well as with the beneficial endophytic fungus Piriformospora indica. The expression of BvGLP-1 in Arabidopsis elevated the H₂O₂ content and conferred significant resistance to V. longisporum and R. solani but did not affect the beneficial interaction with P. indica in seedlings. Microscopic observations revealed a dramatic reduction in the amount of hyphae of the pathogenic fungi on the root surface as well as of fungal mycelium developed inside the roots of transgenic Arabidopsis compared with wild-type plants. Molecular analysis demonstrated that the BvGLP-1 expression in Arabidopsis constitutively activates the expression of a subset of plant defense-related proteins such as PR-1 to PR-4 and PDF1.2 but not PDF2.1 and PDF2.3. In contrast, the PDF2.1 mRNA level was downregulated. These data suggest an important role of BvGLP-1 in establishment of plant defense responses, which follow specific signaling routes that diverge from those induced by the beneficial fungus.