Powdery mildew infection induces a non-canonical route to storage lipid formation at the expense of host thylakoid lipids to fuel its spore production

Powdery mildews are obligate biotrophic fungi that manipulate plant metabolism to supply lipids, particularly during fungal asexual reproduction when fungal lipid demand is extensive. The mechanism for host response to fungal lipid demand has not been resolved. We found storage lipids, triacylglycerols (TAGs), increase by 3.5-fold in powdery mildew-infected tissue. In addition, lipid bodies, not observable in uninfected mature leaves, are present in both cytosol and chloroplasts at the infection site. This is concurrent with decreased thylakoid membrane lipids and thylakoid disassembly. Together, these findings indicate that the powdery mildew induces localized thylakoid membrane degradation to promote storage lipid formation. Genetic analyses show the canonical ER pathway for TAG synthesis does not support powdery mildew spore production. Instead, Arabidopsis DIACYLGLYCEROL ACYLTRANSFERASE 3 (DGAT3), shown to be chloroplast-localized and to be largely responsible for powdery mildew-induced chloroplast TAGs, promotes fungal asexual reproduction. Powdery mildew-induced leaf TAGs are enriched in thylakoid associated fatty acids, which are also present in the produced spores. This research provides new insights on obligate biotrophy and plant lipid metabolism plasticity and function. Furthermore, by understanding how photosynthetically active leaves can be converted into TAG producers, more sustainable and environmentally benign plant oil production could be facilitated.