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Two Closely Related Rho GTPases, CDC42 and RacA, of the Endophytic Fungus Epichloë festucae Have Contrasting Roles for ROS Production and Symbiotic Infection Synchronized with the Host Plant

Summary

This research explores how beneficial fungi live inside grass plants without causing harm. The study reveals that two similar proteins (Cdc42 and RacA) help the fungus grow properly within plant tissues. Understanding this relationship is important because it shows how some microorganisms can live harmoniously with plants instead of causing disease. Impacts on everyday life: – Helps develop better grass varieties for agriculture and lawns by understanding beneficial fungal partnerships – Provides insights for developing more sustainable agricultural practices using beneficial microbes – Could lead to new approaches for protecting plants from harmful fungi – May help in developing stress-resistant grass varieties for sports fields and golf courses – Contributes to understanding how organisms maintain beneficial relationships rather than causing disease

Background

Epichloë festucae is an endophytic fungus that systemically colonizes temperate grasses to establish symbiotic associations. While pathogenic fungi extend their hyphae by tip growth, E. festucae hyphae systemically colonize the intercellular space of expanding host leaves via a unique mechanism of hyphal intercalary growth. Maintaining symptomless infection is a key requirement for endophytes, distinguishing them from pathogenic fungi.

Objective

This study aimed to investigate the distinctive roles of two homologous Rho GTPases, Cdc42 and RacA, in regulating E. festucae growth within host plants. The research focused on understanding the vital role of Cdc42 for intercalary hyphal growth and RacA’s involvement in hyphal network formation, demonstrating how mutations in these genes affect plant tissue infection.

Results

The study found that Cdc42 is essential for intercalary hyphal growth and systemic infection in expanding host leaves, while RacA regulates hyphal network formation through cell-cell fusion. Functions of these proteins are mediated through specific interactions with BemA and NoxR respectively, which are components of the ROS-producing NOX complex. The racA mutant showed abnormal branching and inability to fuse, while the cdc42 mutant exhibited fragmented hyphae in mature leaves. Symbiotic defects in the racA mutant were rescued by introducing modified Cdc42 with key amino acid substitutions crucial for RacA function.

Conclusion

The study demonstrates that E. festucae utilizes two similar small GTPases in unique ways during symbiotic interaction with host plants. RacA and Cdc42 have contrasting roles in ROS production and distinct functions in maintaining symbiotic growth. The specific interactions of these GTPases with BemA and NoxR are crucial for their functional differentiation in symbiotic infection. This research provides important insights into how endophytic fungi maintain controlled growth within host plants.
  • Published in:PLOS Pathogens,
  • Study Type:Experimental Research,
  • Source: 10.1371/journal.ppat.1006840
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