The plant fungal pathogen Fusarium graminearum is the causative agent of Fusarium head blight in wheat and Gibberella stalk rot in maize. It not only causes severe yield loss, but also contaminates grain with its mycotoxins such as deoxynivalenol (DON) that are harmful to humans and animals. Genetic source of complete resistance to F. graminearum in cereal crops is not available to date, which highlights the importance in developing novel solutions based on in-depth understanding of its pathogenicity. So far, F. graminearum pathogenicity in wheat head blight has been extensively studied, whereas little is known about its pathogenicity in maize stalk infection. 

Recently, a team led by Dr. TANG Weihua at Institute of Plant Physiology and Ecology (SIPPE), Shanghai Institutes for Biological Sciences, CAS, in collaboration with Dr. WANG Yufeng at University of Texas at San Antonio, tracked the F. graminearum invasion process inside maize stalk at the cellular level. They discovered that, during the development of Gibberella stalk rot, the fungus takes an intercellular growth route during the early stage, and switches to an intracellular growth route during later stage. Laser microdissection and transcriptomic analysis revealed in planta stage-specific fungal infection dynamics and allowed the inference the stepwise infection strategies that occur within six days post inoculation.  

The results suggest that F. graminearum tailors its infection arsenal (including the dosage of cell wall degradation enzymes and the category and timing of secondary metabolite production) according to host microenvironment conditions, and it launches its defense or survival protocols (including detoxification machinery, phosphorus limitation solutions, and ferric limitation solutions) when needed.  

Most significantly, subsequent system analysis and experimental validation elucidated that F. graminearum remodels membrane lipids to overcome the phosphate limitation in the intercellular space of maize stalks during the disease progression, revealing a novel adaptive strategy to increase the within-host fitness of this pathogen of critical agricultural and economic importance.  

This study also revealed that the intercellular space of maize stalk is phosphorus limited, and the early intercellular growth capacity is critical for F. graminearum causing stalk rot disease in maize. 

The study entitled “Cellular Tracking and Gene Profiling of Fusarium graminearum during Maize Stalk Rot Disease Development Elucidates its Strategies in Confronting Phosphorus Limitation in the Host Apoplast” was published in PLOS Pathogens on Mar. 31, 2016.  

This work was supported by the grants from the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB11020500) and National Basic Research Program of China (2011CB100702). SIPPE core facility provided strong technical support. 

Figure. The nonphosphorus membrane lipid synthase BTA1 allows the fungal pathogen Fusarium graminearum to overcome phosphate limitation during intercellular invasion inside maize stalk. (Images by Dr. TANG Weihua’s lab)