The rare sugar D-tagatose protects plants from downy mildews and is a safe fungicidal agrochemical

The rare sugar D-tagatose is a safe natural product used as a commercial food ingredient. Here, we show that D-tagatose controls a wide range of plant diseases and focus on downy mildews to analyze its mode of action. It likely acts directly on the pathogen, rather than as a plant defense activator. Synthesis of mannan and related products of D-mannose metabolism are essential for development of fungi and oomycetes; D-tagatose inhibits the first step of mannose metabolism, the phosphorylation of D-fructose to D-fructose 6-phosphate by fructokinase, and also produces D-tagatose 6-phosphate. D-Tagatose 6-phosphate sequentially inhibits phosphomannose isomerase, causing a reduction in D-glucose 6-phosphate and D-fructose 6-phosphate, common substrates for glycolysis, and in D-mannose 6-phosphate, needed to synthesize mannan and related products. These chain-inhibitory effects on metabolic steps are significant enough to block initial infection and structural development needed for reproduction such as conidiophore and conidiospore formation of downy mildew.

Susumu Mochizuki, Takeshi Fukumoto, Toshiaki Ohara, Kouhei Ohtani, Akihide Yoshihara, Yoshio Shigematsu, Keiji Tanaka, Koichi Ebihara, Shigeyuki Tajima, Kenji Gomi, Kazuya Ichimura, Ken Izumori, Kazuya Akimitsu