Loss of E3 ligase HvST1 function substantially increases distal crossover frequency.

Area of Science:

• Plant genetics
• Molecular biology
• Meiosis research

Background:

• Cereal crops like barley have limited genetic recombination due to crossover restriction in distal chromosomal regions.
• Understanding the genetic regulation of crossover (CO) frequency and distribution is vital for improving breeding flexibility in large-genome cereals.

Purpose of the Study:

• To characterize the function of the grass-specific E3 ubiquitin ligase, HvST1, in regulating synapsis and CO formation during meiosis in barley (Hordeum vulgare).

Main Methods:

• Fine mapping and CRISPR/Cas9 gene editing to identify and validate the HvST1 mutation.
• In vitro ubiquitination assays to assess HvST1 activity on substrates like ASY1.
• Structured illumination microscopy and immunolocalization to analyze meiotic progression and synaptonemal complex (SC) protein dynamics.

Main Results:

• Loss of HvST1 function resulted in disrupted SC formation, persistent ASY1 signals, and aberrant ZYP1 polycomplexes.
• Hvst1 mutants exhibited a significant increase in distal CO frequency despite impaired synapsis.
• HvST1 was demonstrated to ubiquitinate ASY1 in vitro, suggesting a role in chromosome axis protein turnover.

Conclusions:

• HvST1 is essential for normal synapsis and regulates CO distribution during barley meiosis.
• HvST1's loss disrupts SC progression but enhances distal CO formation, revealing a novel ubiquitination-based mechanism for recombination modulation in grasses.