A cell surface-exposed protein complex with an essential virulence function in Ustilago maydis.

Area of Science:

• Plant Pathology
• Mycology
• Molecular Plant-Microbe Interactions

Background:

• Plant pathogenic fungi secrete effector proteins to manipulate host cells and evade immunity.
• Fungal effector delivery mechanisms into host cells remain largely unknown, unlike bacterial systems.

Purpose of the Study:

• To investigate the delivery system of effector proteins in the biotrophic fungus Ustilago maydis.
• To identify the molecular components and function of a potential fungal effector translocation complex.

Main Methods:

• Genetic analysis of Ustilago maydis mutants lacking specific effector and membrane proteins.
• Co-expression analysis of genes encoding the identified complex members.
• Microscopy to visualize the localization and interaction of the protein complex with host cells.

Main Results:

• A stable complex of five effectors and two membrane proteins was identified in Ustilago maydis.
• This complex is co-regulated, expressed during fungal colonization, and essential for suppressing plant defenses.
• The complex is anchored in the fungal membrane, extends into host cells, and interacts with plant plasma membrane proteins.

Conclusions:

• Ustilago maydis utilizes a conserved protein complex for effector translocation, a novel mechanism in fungi.
• This complex is crucial for fungal pathogenicity by suppressing host immunity.
• The conserved nature of this complex across smut fungi presents a promising target for novel fungicide development.