Ras subfamily GTPases regulate development, aflatoxin biosynthesis and pathogenicity in the fungus Aspergillus flavus

Area of Science:

• Molecular biology
• Mycology
• Signal transduction

Background:

• Ras subfamily proteins act as molecular switches in eukaryotic signal transduction.
• These proteins regulate diverse cellular processes.
• Six Ras subfamily genes (rasA, rasB, rasC, rab-33, rheb, rsr1) were identified in Aspergillus flavus.

Purpose of the Study:

• To investigate the roles of Ras subfamily proteins, specifically rsr1 and rheb, in Aspergillus flavus.
• To understand the impact of rsr1 and rheb deletions on fungal growth, development, and toxin production.
• To explore the functional relationships and potential redundancies among Ras subfamily proteins in A. flavus.

Main Methods:

• Gene deletion mutagenesis to create rsr1, rheb, and double mutants (∆rsr1, ∆rheb, ∆rheb/rsr1).
• Phenotypic analysis of growth, sporulation, sclerotia formation, and aflatoxin production.
• Quantitative proteomics to identify differentially expressed proteins (DEPs) in mutant strains.
• Protein-protein interaction network analysis to identify interacting partners, such as SepA.

Main Results:

• ∆rsr1, ∆rheb, and ∆rheb/rsr1 mutants showed significantly reduced growth and sporulation.
• Sclerotia formation decreased in ∆rheb and ∆rheb/rsr1 but increased in ∆rsr1.
• Aflatoxin production increased in ∆rheb but decreased in ∆rsr1 and ∆rheb/rsr1.
• Quantitative proteomics revealed 520 DEPs for ∆rsr1 and 133 DEPs for ∆rheb.
• The cytokinesis protein SepA was identified in the rsr1 protein-protein interaction network, affecting growth and aflatoxin biosynthesis.

Conclusions:

• Rsr1 and Rheb are critical for A. flavus pathogenicity.
• Ras subfamily proteins exhibit functional redundancy and specific differences in A. flavus.
• Rsr1 plays a regulatory role in the function of SepA, impacting fungal growth and aflatoxin production.