Format: ORAL

Gentaro Shigita1,2, Edgardo M. Ortiz1, Alina Hwener3, Hiroshi Ezura2, Hanno Schaefer1

1 Technical University of Munich, Freising, Germany 2 University of Tsukuba, Tsukuba, Japan 3 Ludwig Maximilian University of Munich, Munich, Germany

The island syndrome is a recurring pattern in ecological and morphological differences between insular species and their continental relatives, typically involving loss of defensive structures, increased woodiness, and modifications in floral and reproductive traits. Although this phenomenon has long been treated as a textbook example of adaptive evolution, the underlying genetic mechanisms remain largely unknown. The cucumber tree (Dendrosicyos socotranus Balf.f.) is endemic to Socotra island, Yemen, and the only arborescent species among ~1,000 Cucurbitaceae species. Its anatomical features demonstrate adaptation to Socotras seasonally dry habitat by storing water in the parenchyma of its swollen stems, allowing extended photosynthesis during the dry season. Moreover, the species attracts additional attention due to its vulnerable status on the IUCN Red List and its cultural significance for local communities as a source of fodder and medicine. Here, we report the first genomic exploration of D. socotranus. Based on k-mer spectrum analyses, the species is estimated to be diploid, with a ~400 Mb genome. Using a combination of Nanopore long-reads and Illumina short-reads, the genome was assembled into 181 contigs, totaling 405.9 Mb with an N50 of 4.9 Mb, and 97.7% BUSCO completeness. Genome annotation revealed that 65.4% of the genome consists of repeats and contains 19,241 protein-coding genes. Comparative genomics with 22 other cucurbits identified 7,592 gene families conserved across all examined cucurbits, as well as 19 gene families unique to D. socotranus. Functional annotation of these 19 gene families found one gene family presumably associated with self-incompatibility, suggesting a potential shift in the reproductive manner as observed in other insular species. Further analyses of this genome and comparison with its closest continental relatives will provide valuable insights into the genetic mechanisms that makeD. socotranusoutstanding in the family and facilitate our understanding of adaptive evolution on islands.