GH64 Enzyme Helps Root Fungus Infect Multiple Plant Hosts

Researchers have identified a fungal enzyme that helps a widespread root colonizer infect more than one plant host. The Nature Microbiology study, published on October 1, traced the role of a GH64 beta-1,3-glucanase in Plectosphaerella cucumerina and then tested the same enzyme family in a second pathogen, Colletotrichum incanum. The result points to a shared molecular route for root infection, but it does not yet amount to a field-ready crop protection target.

The work began with a large survey of the Arabidopsis root mycobiome. Researchers reanalysed 26.98 million fungal sequence reads from 291 root samples collected at 18 European sites. Only five fungal sequence variants occurred in more than 80 percent of samples. One of them was assigned to P. cucumerina, a soil-borne fungus associated with damping-off and root or crown rot in several plants.

The team assembled 72 Plectosphaerella isolates from diverse plants and environments around the world and generated long-read genome assemblies. Sixty-nine belonged to the P. cucumerina species complex. Genetic variation followed fungal phylogeny more strongly than the identity of the plant from which each isolate had been collected, suggesting that host origin alone did not explain the fungus’s broad colonization range.

Multihost experiments showed an important biological boundary. P. cucumerina caused root disease in Arabidopsis and tomato, both dicots, but did not invade barley roots in the same way. Microscopy found fungal growth near barley root hairs without endophytic proliferation, while Arabidopsis and tomato roots showed internal colonization. The authors link that contrast partly to differences in cell-wall composition and host responses.

Transcriptome analysis showed that the fungus changed its cell-wall-degrading enzyme programme according to the host. When researchers disrupted the GH64 gene, pathogenicity fell by 62 to 77 percent in Arabidopsis and tomato, while root colonization declined by 18 to 24 percent. The mutants grew normally in artificial medium, strengthening the case that the gene affected host infection rather than general fungal fitness.

A second experiment tested whether the mechanism extended beyond Plectosphaerella. Inactivating the GH64 gene in Colletotrichum incanum reduced the fungal load in Arabidopsis roots by 68.5 percent and increased plant shoot fresh weight by 10 percent compared with plants exposed to the wild-type pathogen. The same mutation did not produce a significant effect in Nicotiana benthamiana, where GH64 expression was much lower.

For crop science, the practical importance lies in target discovery. A conserved enzyme that pathogens activate inside susceptible roots could guide future work on resistant germplasm, diagnostics or narrowly targeted disease controls. The host-specific results also warn against treating a molecular target as universally important. A useful intervention would need to work in the crop, pathogen strain and root environment where the gene is actually active.

This remains mechanistic research conducted with model plants and controlled infection assays, not evidence that blocking GH64 will protect commercial fields. Soil microbial communities can restrain fungi that cause disease in simplified laboratory systems, and natural disease depends on environment, crop genetics and other microbes. Field validation, delivery methods and off-target effects must be resolved before the finding can support a commercial technology.