A maize-specifically expressed gene cluster in Ustilago maydis

Area of Science:

• Plant Pathology
• Fungal Genetics
• Molecular Biology

Background:

• Ustilago maydis is an obligate biotrophic pathogen of maize.
• The pathogen requires its host for development and sexual cycle completion.
• Specific fungal genes are likely involved in host-pathogen interactions.

Purpose of the Study:

• Identify and characterize novel genes involved in the biotrophic stage of Ustilago maydis.
• Investigate the regulation, function, and evolution of the identified mig2 gene cluster.
• Elucidate the potential role of the mig2 cluster in host-pathogen interactions.

Main Methods:

• Gene expression analysis (identifying mig2-1 expression during biotrophy).
• Promoter deletion analysis to study gene regulation.
• Bioinformatic analysis to predict protein function and identify secretion signals.
• Gene deletion and fusion protein experiments (Mig2-1-eGFP) to confirm secretion.
• Comparative genomics across Ustilago maydis strains and related species.

Main Results:

• Identified the fungal mig2-1 gene specifically expressed during the biotrophic stage.
• Discovered mig2-1 is part of a five-gene cluster (mig2-1 to mig2-5) with similar regulation.
• Demonstrated functional N-terminal secretion signals for Mig2 proteins, with secretion confirmed for Mig2-1.
• Observed conserved C-termini with eight cysteine residues and variable central domains in Mig2 proteins.
• Found the mig2 cluster is conserved in U. maydis but lost in some South American isolates and absent in Ustilago scitaminea.

Conclusions:

• The mig2 gene cluster encodes secreted proteins potentially involved in Ustilago maydis-maize interactions.
• The cluster's regulation involves both positive and negative elements.
• Evolutionary analysis suggests gene loss and potential divergence in host specificity.
• The mig2 cluster likely plays a significant role in governing host interaction during pathogenesis.