Corn Smut Fungus Uses Multiple Pathways to Metabolize Sucrose, Switching Strategies Based on Growth Stage
Researchers have mapped the complete sucrose utilization system of Ustilago maydis, a corn pathogen, uncovering a surprising lifestyle-dependent switch between two distinct metabolic strategies. The fungus uses an unconventional pathway involving a repurposed maltose transporter and intracellular enzymes during yeast-like growth, but shifts to a canonical sucrose uptake pathway during infection of host plants. This finding challenges assumptions about fungal sugar metabolism and suggests flexible carbon acquisition may be a widespread adaptive strategy among basidiomycete pathogens.
A new preprint study published on bioRxiv investigates how the corn smut fungus Ustilago maydis acquires sucrose, the primary sugar transported in plants and a key nutrient for plant-pathogenic fungi. The researchers characterized a secreted invertase called Suc2, finding it adopts a dimeric architecture that appears to be the predominant form across fungal homologs, contrary to the higher-order oligomeric structures previously described in baker's yeast. Strikingly, deletion experiments showed that neither Suc2 nor the canonical sucrose transporter Srt1 nor the cytosolic hydrolase Suc1 was individually required for yeast-like growth on sucrose. Instead, the fungus relies on a repurposed non-canonical module—the maltose transporter Agt1 paired with intracellular (iso)maltases—to metabolize sucrose during its free-living yeast-like stage. However, during pathogenic development and host infection, the fungus switches to the canonical intracellular sucrose utilization pathway mediated by Srt1 and Agt1. This lifestyle-dependent metabolic switch reveals an unexpected redundancy and flexibility in fungal carbon acquisition, with potential implications for understanding how basidiomycete pathogens adapt to different environments and host conditions.
What's missing
As a preprint, this study has not yet undergone formal peer review, so findings should be interpreted with caution. The authors do not fully address whether the non-canonical Agt1-based pathway is unique to U. maydis or how widespread this metabolic flexibility is across other basidiomycete pathogens, beyond speculating it may be common. The fitness consequences of each pathway during actual field infection conditions, and whether disrupting both pathways simultaneously would fully abolish pathogenicity, remain open questions.
What different sources said
- bioRxivCenter
Disentangling the sucrose metabolism of the corn smut Ustilago maydis reveals unexpected complexity
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