Thiamine is a vitamin for plant-pathogenic powdery mildew fungi

Thiamine (vitamin B1) is an essential micronutrient in all forms of life that serves as a cofactor for several enzymes in primary metabolism. Plant-pathogenic and obligate biotrophic powdery mildew fungi appear to be auxotrophic for the micronutrient, as they have lost the majority of the genes needed for thiamine biosynthesis. Using the barley powdery mildew pathogen, <i>Blumeria hordei</i>, as a study object, we found that (1) asexual conidiospores contain detectable levels of thiamine, (2) the <i>B. hordei THI80</i> gene encodes a functional thiamine pyrophosphokinase, and (3) <i>B. hordei</i> has a functional DUR31-like thiamine transporter likely localizing to the cell surface. We further demonstrated a requirement of the metabolite for the activity of <i>B. hordei</i> transketolase, an enzyme of central carbon metabolism known to be thiamine-dependent in other organisms. Taken together, our data suggest that thiamine is a vitamin for <i>B. hordei</i> and, thus, likely all powdery mildew fungi.