An S-RNase-based gametophytic self-incompatibility system evolved only once in eudicots.

Area of Science:

• Plant evolutionary biology
• Molecular genetics
• Reproductive biology

Background:

• The S-RNase-based gametophytic self-incompatibility (GSI) system is thought to originate from the common ancestor of many dicots.
• S-RNase genes are expected in GSI-possessing families, and their duplicates may gain new functions in non-GSI families.
• Previously, S-RNase lineage sequences were only identified in Solanaceae, Scrophulariaceae, Rosaceae, Cucurbitaceae, and Fabaceae.

Purpose of the Study:

• To discover novel sequences belonging to the S-RNase lineage in plant families.
• To evaluate the efficacy of phylogenetic and amino acid pattern-based approaches for S-RNase lineage discovery.
• To investigate the evolutionary history and functional diversification of S-RNase genes.

Main Methods:

• Phylogenetic analysis of gene sequences.
• Amino acid pattern-based screening for S-RNase lineage genes.
• Bayeisan constrained tree analyses to infer evolutionary relationships.

Main Results:

• Identified S-RNase lineage genes in three new plant families: Rubiaceae, Euphorbiaceae, and Malvaceae.
• Demonstrated that both phylogenetic and pattern-based methods have similar false-negative rates (~10%), with the pattern-based approach yielding ~15% false positives.
• Found evidence for frequent acquisition of new functions by S-RNase lineage genes.
• Discovered a putative S-RNase sequence in Lotus, a genus lacking prior molecular GSI studies.
• Supported the hypothesis of a single S-RNase-based GSI origin predating Asteridae and Rosidae split.

Conclusions:

• The S-RNase gene family is more widespread than previously known, extending to Rubiaceae, Euphorbiaceae, and Malvaceae.
• Functional diversification of S-RNase lineage genes is a common evolutionary event.
• The findings reinforce the ancient origin of S-RNase-based GSI and its widespread presence across major dicot lineages.