Allotetraploid nature of a wild potato species, Solanum stoloniferum Schlechtd. et Bché., as revealed by whole-genome sequencing

Mexican wild diploid potato species are reproductively isolated from A-genome species, including cultivated potatoes; thus, their genomic relationships remain unknown. Solanum stoloniferum Schlechtd. et Bché. (2n = 4x = 48, AABB) is a Mexican allotetraploid species frequently used in potato breeding. We constructed a chromosome-scale assembly of the S. stoloniferum genome using PacBio long-read sequencing and Hi-C scaffolding technologies. The final assembly consisted of 1742 Mb, among which 745 Mb and 713 Mb were anchored to the 12 A-genome and 12 B-genome chromosomes, respectively. Using the RNA-seq datasets, we detected 20 994 and 19 450 genes in the A and B genomes, respectively. Among these genes, 5138 and 3594 were specific to the A and B genomes, respectively, and 15 856 were homoeologous, of which 18.6-25.4% were biasedly expressed. Structural variations such as large pericentromeric inversions were frequently found between the A- and B-genome chromosomes. A comparison of the gene sequences from 38 diverse genomes of the related Solanum species revealed that the S. stoloniferum B genome and Mexican diploid species, with the exception of S. verrucosum, were monophyletically distinct from the S. stoloniferum A genome and the other A-genome species, indicating that the Mexican diploid species share the B genome. The content and divergence of transposable elements (TEs) revealed recent bursts and transpositions of TEs after polyploidization. Thus, the S. stoloniferum genome has undergone dynamic structural differentiation and TE mobilization and reorganization to stabilize the genomic imbalance. This study provides new insights into polyploid evolution and the efficient use of allotetraploid species in potato breeding.