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Enhancing type II-resistance in crops through modification of the cell wall polymer callose

Tobias Hanak: University of Hamburg

<div>Food supply and security are two major challenges of mankind due to an increasing world population and climate change. Therefore, new strategies for enhancing plant defence against pathogens are required. To test new approaches in molecular crop breeding, we aim to modify the biosynthesis of the (1,3)-<em>β</em>-glucan cell wall polymer callose, known for its importance in plant defence and stress response in <em>Brachypodium distachyon</em> a model plant for crops and wheat (<em>Triticum aestivum</em>). We previously showed that overexpression (OE) of the stress-induced callose synthase <em>PMR4</em> in <em>Arabidopsis thaliana</em> induced complete penetration resistance to powdery mildew through enhanced callose deposition. Now we overexpressed <em>PMR4</em> and its possible homolog <em>BdGSL3</em> in <em>B</em>. <em>distachyon</em>. Both <em>B. distachyon</em> OE lines revealed a so-called type II resistance to the fungal crop pathogen <em>Fusarium graminearum</em>. The pathogen was only able to infect the directly inoculated floret. Enhanced callose deposition in the spikelets phloem prevented further colonization of the spikelet. In wheat lines overexpressing <em>PMR4</em>, we also observed a stronger type II-resistance to <em>F</em>. <em>graminearum</em> associated with enhanced callose deposition. CRISPR/Cas9-mediated disruption of <em>BdGSL3</em> in <em>B</em>. <em>distachyon</em> indicates its involvement in stress-induced callose depositions. In conclusion, we identified callose biosynthesis as a tool for enhancing resistance to fungal pathogens in crops and the involvement of <em>BdGSL3</em> in stress response.</div>