A Super-Pangenome for Cultivated Citrus Reveals Evolutive Features During the Allopatric Phase of Their Reticulate Evolution.

The main genetic diversity observed in cultivated citrus results from a reticulate evolution involving four ancestral taxa whose radiation occurred in allopatry. In such context, GWAS analysis, genome diversity and transcriptomic studies will be significantly enhanced through pangenome approaches. We report the implementation of a super-pangenome for cultivated citrus, established with de novo assemblies of C. medica, C. reticulata and C. micrantha, released for the first time alongside a published chromosome-scale assembly of C. maxima. Repetitive element annotation revealed that half of each genome consisted of transposable elements or DNA-satellites. The new genome assemblies display strong synteny and collinearity, while discrepancies are observed with the C. maxima assembly. Resequencing information from 55 accessions helped to explore the intra- and interspecific diversity of the ancestral taxa and their relationships with horticultural groups. Diagnostic SNPs of the ancestral taxa revealed interspecific introgressions in several representative accessions of C. reticulata, C. maxima and C. medica as well as insights into the origin and phylogenomic structures of horticultural groups. PAV analysis revealed a gene whose absence or presence was specific to one of the ancestral taxa. Diagnostic PAV analysis uncovered a large chloroplastic introgression in C. medica chromosome 4. The analysis of the functional enrichment and species-specific adaptations in the citrus super-pangenome revealed distinct functional specialisations. This highlights the evolutionary paths that have shaped species, contributing to the diversity in the citrus super-pangenome while maintaining a shared foundation of essential biological processes. We established a Genome Hub, offering a platform for continuous genomic research.