Genomic insights into Castanopsis carlesii and Castanea henryi: flower and fruit development and evolution of NLR genes in the beech-oak family

The Fagaceae family, comprising over 900 species, is an essential component of Northern Hemisphere forest ecosystems. However, genomic data for tropical and subtropical genera Castanopsis and Castanea remain limited compared to the well-studied oak. Here, we present chromosome-level genome assemblies of Castanopsis carlesii and Castanea henryi, with assembled genome sizes of 927.24 Mb (N50 = 1.57 Mb) and 780.10 Mb (N50 = 1.07 Mb), respectively, and repetitive sequence contents of 45.79% and 44.88%. Comparative genomic analysis revealed that the estimated divergence time between Castanopsis and Castanea was determined to be 48.3 Mya and provided evidence that both genera experienced only one of the ancient whole genome triplication event (γ event) shared with most eudicots. The development of C. carlesii flower bracts and cupules was controlled by A- and E-class genes, suggesting that the cupules may originate from the bracts. Additionally, genes involved in sucrose and starch metabolism genes played distinct roles during C. carlesii fruit development. The amplification of the nucleotide-binding leucine-rich repeat (NLR) gene family in Fagaceae exhibited similarities, indicating that this expansion may be an adaptation to similar environmental pressures. This study provides valuable genomic resources for Asian Fagaceae and enhances our understanding of Fagaceae evolution.