The genomes of pecan and Chinese hickory provide insights into Carya evolution and nut nutrition

Background: Pecan (Carya illinoinensis) and Chinese hickory (C. cathayensis) are important commercially cultivated nut trees in the genus Carya (Juglandaceae), with high nutritional value and substantial health benefits. Results: We obtained >187.22 and 178.87 gigabases of sequence, and similar to 288x and 248x genome coverage, to a pecan cultivar (Pawnee) and a domesticated Chinese hickory landrace (ZAFU-1), respectively. The total assembly size is 651.31 megabases (Mb) for pecan and 706.43 Mb for Chinese hickory. Two genome duplication events before the divergence from walnut were found in these species. Gene family analysis highlighted key genes in biotic and abiotic tolerance, oil, polyphenols, essential amino acids, and B vitamins. Further analyses of reduced-coverage genome sequences of 16 Carya and 2 Juglans species provide additional phylogenetic perspective on crop wild relatives. Conclusions: Cooperative characterization of these valuable resources provides a window to their evolutionary development and a valuable foundation for future crop improvement.