The cytonuclear dimension of allopolyploid evolution: an example from cotton using rubisco

Area of Science:

• Evolutionary Biology
• Genetics
• Plant Science

Background:

• Allopolyploid speciation involves merging divergent genomes, typically retaining only one set of organellar genomes.
• Rubisco, comprising nuclear small subunits (SSUs) and plastid large subunits (LSUs), is crucial for photosynthesis and serves as a model for cytonuclear evolution.

Purpose of the Study:

• To investigate the evolutionary process of cytonuclear accommodation in Gossypium allopolyploids.
• To analyze the evolution of Rubisco small subunit (rbcS) genes and their interaction with the large subunit (rbcL) following polyploidization.

Main Methods:

• Sequencing of LSU genes from diploid progenitors and allopolyploid species.
• Analysis of rbcS gene family sequences to detect recombination events.
• Transcriptome analysis to assess gene expression patterns of rbcS homoeologs.

Main Results:

• Nonsynonymous substitutions were observed in LSU genes, suggesting differential selection on rbcS partners.
• Nonreciprocal homoeologous recombination (gene conversion) occurred between A- and D-rbcS homoeologs in allopolyploids.
• A-homoeologs of rbcS were preferentially expressed in allopolyploids and hybrids, aligning with maternal rbcL origin.
• Mutations in some progenitor rbcS genes suggest ongoing cytonuclear coevolution.

Conclusions:

• Gossypium allopolyploids exhibit evidence of cytonuclear coevolution, particularly in the Rubisco system.
• Gene conversion and biased gene expression are key mechanisms shaping nuclear-plastid interactions post-polyploidization.
• The Rubisco system provides insights into the rapid adaptation and evolutionary trajectories of allopolyploids.