Crossover formation during rice meiosis relies on interaction of OsMSH4 and OsMSH5

Area of Science:

• Genetics
• Molecular Biology
• Plant Science

Background:

• MSH4 is a MutS protein involved in meiosis across eukaryotes.
• Mutations in MSH4 lead to reduced chiasmata and meiotic defects in various species.
• Understanding MSH4 function in rice is vital for crop improvement.

Purpose of the Study:

• To characterize the function of rice MSH4 (OsMSH4) in meiosis.
• To investigate the role of OsMSH4 in chiasma formation and recombination.
• To elucidate the interaction of OsMSH4 with other meiotic proteins in rice.

Main Methods:

• Map-based cloning was used to identify and characterize rice MSH4.
• Analysis of chiasma frequency in wild-type and Osmsh4 mutant rice.
• Double mutant analysis with other ZMM proteins (e.g., Osmsh5).
• Yeast two-hybrid and pull-down assays to verify protein interactions.

Main Results:

• Osmsh4 mutants exhibited a drastic reduction in chiasma frequency (∼10% of wild type).
• Synaptonemal complex formation remained normal in Osmsh4 mutants.
• OsMSH4 and OsMSH5 act earlier than other ZMM proteins, potentially stabilizing early Holliday junctions.
• Direct physical interactions between OsMSH4-OsMSH5 and OsMSH5-OsHEI10 were confirmed.

Conclusions:

• OsMSH4, in complex with OsMSH5, plays a critical role in promoting the majority of crossovers (COs) in rice meiosis.
• This OsMSH4-OsMSH5 complex likely stabilizes progenitor and double Holliday junctions.
• The findings provide insights into the conserved mechanism of crossover formation in plants.