Reticulate Evolution in AA-Genome Wild Rice in Australia

Area of Science:

• Genetics
• Evolutionary Biology
• Botany

Background:

• The Australian wild rice (AA-genome) gene pool is geographically and genetically distinct from Asian wild rice.
• Two distinct taxa, *Oryza meridionalis* and an *Oryza rufipogon*-like species, coexist in northern Australia.
• Previous studies noted rare intermediate plants despite a reported reproductive barrier between these taxa.

Purpose of the Study:

• To investigate hybridization events between Australian wild rice taxa using genome sequencing.
• To analyze the genetic makeup of intermediate morphology plants and determine their hybrid origin.
• To understand the role of reticulate evolution in Australian wild rice populations.

Main Methods:

• Resequencing of chloroplast and nuclear genomes from 26 wild rice populations.
• Comparative genomic analysis to identify hybridisation and introgression.
• Examination of specific genes, including starch biosynthesis genes, for allelic variation.

Main Results:

• Genomic analysis confirmed bidirectional hybridization between *O. meridionalis* and the *O. rufipogon*-like taxa.
• Intermediate morphology plants exhibited high nuclear genome heterozygosity, indicative of hybrid origin.
• Evidence of heterozygotes with alleles from both parental species suggests early-generation hybrids.

Conclusions:

• Reticulate evolution, including hybridization and chloroplast capture, is an ongoing process in Australian wild rice.
• Hybridization events may have played a crucial role in the broader evolution and domestication of rice.
• Rare hybrids with low cross-fertility might contribute to the persistence of distinct wild rice species.