Oxaloacetate anaplerosis differently contributes to pathogenicity in plant pathogenic fungi Fusarium graminearum and F. oxysporum

Summary

Two important crop-destroying fungi, Fusarium graminearum and F. oxysporum, rely differently on a metabolic enzyme called pyruvate carboxylase to cause disease. Researchers found that removing this enzyme completely eliminates the ability of F. oxysporum to infect tomato plants by blocking its capacity to penetrate roots and break down plant cell walls. However, the same enzyme deletion has minimal effect on F. graminearum’s ability to infect wheat, suggesting these fungi have evolved different metabolic strategies for attacking their hosts.

Background

Anaplerosis replenishes metabolic intermediates in the tricarboxylic acid (TCA) cycle through enzymatic reactions. Pyruvate carboxylase (PYC) catalyzes pyruvate carboxylation to form oxaloacetate, a key TCA intermediate. Although PYC orthologs are conserved across organisms, their pathobiological functions in filamentous pathogenic fungi remain poorly understood.

Objective

To investigate the molecular functions of the PYC1 ortholog gene in Fusarium graminearum and F. oxysporum, two prominent fungal plant pathogens with distinct pathosystems. The study aimed to elucidate variations in carbon metabolism and how PYC1-mediated anaplerosis affects fungal development and pathogenicity.

Results

PYC1 deletion had species-specific effects: F. oxysporum deletion mutants exhibited severe defects in hyphal growth, conidiation, and virulence, while F. graminearum deletion did not significantly impact virulence. Metabolomic analysis revealed distinct reprogramming in central carbon and nitrogen metabolism, with alpha-ketoglutarate specifically downregulated in F. oxysporum mutants. S-adenosyl-L-methionine and S-methyl-5-thioadenosine showed positive correlation with pathogenicity.

Conclusion

PYC1-mediated anaplerosis differently contributes to pathogenicity between the two Fusarium species, with more pronounced effects in F. oxysporum. PYC1 is essential for penetration, root colonization, and pectin utilization in F. oxysporum, demonstrating how carbon metabolism variations reflect species-specific differences in pathogenic mechanisms and host interaction strategies.
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