Chromosome-Level Genome Assembly of Strauchbufo raddei and Multi-Omic Insights Into Drought Adaptation

Understanding how amphibians adapt to terrestrial and arid environments is important for elucidating vertebrate terrestrialization. In this study, we present the first chromosome-level, high-quality genome assembly of Strauchbufo raddei, constructed using PacBio HiFi long-read sequencing and Hi-C scaffolding. The assembled genome is 4.47 Gb in size, with a scaffold N50 of 575 Mb and 94.5% BUSCO completeness, and 99.8% of sequences anchored to 11 chromosomes, providing a valuable genomic resource for amphibian evolutionary and ecological studies. Comparative genomic analyses identified 163 significantly expanded gene families in the S. raddei lineage, including transposable-element-associated and immune-related gene families. These expansions suggest lineage-specific genomic contributions to immune and barrier-associated adaptations in xeric environments. To further explore these adaptations, we integrated comparative genomics with transcriptomic data and physiological assays across Xenopus tropicalis, Bufo gargarizans, and S. raddei. Notably, although S. raddei lacks the dermal calcified layer present in B. gargarizans, it exhibits comparable water retention and rehydration capacities. Desiccation experiments demonstrated that S. raddei dynamically modulates epidermal thickness and mucus secretion under dehydration. Transcriptomic analyses revealed upregulation of keratin (KRT) genes and activation of pathways related to epidermal integrity and water balance. Phylogenetic analysis of the KRT gene family identified a lineage-specific expansion in bufonid toads, particularly within KRT10- and KRT14-associated subclades. Together, this study provides a high-quality genomic resource for S. raddei and offers integrative insights into the molecular and physiological basis of amphibian adaptation to arid environments.