Convergent evolution at the gametophytic self-incompatibility system in Malus and Prunus

Area of Science:

• Plant reproductive biology
• Molecular evolution
• Genomics

Background:

• S-RNase-based gametophytic self-incompatibility (GSI) is crucial for plant reproduction.
• The evolution of GSI in Rosaceae is complex, with variations in pistil and pollen gene numbers between lineages like Prunus and Pyreae.
• This suggests potential non-orthologous gene evolution within the Rosaceae family.

Purpose of the Study:

• To investigate the evolutionary history of S-RNase and pollen-associated genes in Rosaceae.
• To determine if the GSI systems in different Rosaceae lineages are homologous or paralogous.
• To clarify the independent evolution of GSI in Malus.

Main Methods:

• Phylogenetic analyses of S-RNase and S-pollen lineage genes from five Rosaceae species (Malus domestica, Prunus persica, Prunus mume, Fragaria vesca, Fragaria nipponica).
• Genome-wide characterization of these gene lineages.
• RNA sequencing to analyze gene expression patterns.

Main Results:

• Phylogenetic analyses revealed distinct gene lineages for S-RNase and S-pollen genes in Malus and Prunus.
• Fragaria species only possess Prunus-like S-RNase and SFB-lineage genes.
• The ancestral S-RNase lineage gene is pistil-specific, while the ancestral S-pollen lineage gene is expressed in non-pollen tissues.

Conclusions:

• The S-RNase-based GSI system in Malus (apple) evolved independently from the ancestral Rosaceae system.
• The GSI systems in Prunus and Malus are not orthologous, indicating separate evolutionary trajectories.
• Gene expression patterns support the distinct roles of ancestral S-RNase and S-pollen genes.