A search for synaptonemal complexes in Ustilago maydis

Area of Science:

• * Molecular and Cellular Biology
• * Mycology
• * Genetics

Background:

• * Ustilago maydis is a fungal pathogen that causes significant crop losses.
• * Understanding its reproductive cycle, including meiosis, is crucial for developing control strategies.
• * Synaptonemal complexes (SCs) are key structures involved in homologous chromosome pairing during meiosis.

Purpose of the Study:

• * To investigate the presence and behavior of synaptonemal complexes (SCs) during the life cycle of Ustilago maydis.
• * To determine if SCs are formed during spore development and germination in Ustilago maydis.
• * To explore potential explanations for the absence of observed SCs.

Main Methods:

• * Microscopic examination of germinating spores, germ-tubes (promycelia), gall tissue, and developing spores.
• * Analysis of cell types within the Ustilago maydis gall, including ploidy levels.
• * Comparison with SC presence in other yeast species like Schizosaccharomyces pombe and Saccharomyces cerevisiae.

Main Results:

• * Synaptonemal complexes (SCs) were not detected in any examined cell types of Ustilago maydis, including germinating spores, germ-tubes, gall tissue, and developing spores.
• * The Ustilago maydis gall primarily contains haploid uninucleate cells, with a rare diploid cell observed.
• * Evidence suggests haploid cells fuse to form heterokaryotic or diploid cells before spore formation, with a presumed heterokaryotic phase for infection establishment.

Conclusions:

• * Ustilago maydis may lack synaptonemal complexes (SCs), similar to some other yeasts.
• * Alternatively, SCs might form transiently or be obscured by spore walls, making them difficult to detect with current methods.
• * The life cycle involves a yeast-like haploid phase, fusion, and a heterokaryotic stage preceding sporulation and infection.