Whole-genome sequencing and genome-wide transcriptome profiling of the freshwater planorbid snail Bulinus ugandae (Mollusca: Gastropoda), a Nilotic bulinine refractory to Schistosoma haematobium.

We present the first nuclear genome sequence and extensive genome-wide transcriptomic data for Bulinus ugandae, a freshwater snail native to the Nile drainage, including Lake Victoria, Africa's largest lake. B. ugandae belongs to the B. africanus species group within the genus Bulinus (Gastropoda: Planorbidae) and serves as a vector for Schistosoma bovis, the causative agent of schistosomiasis in livestock, but appears to be refractory to S. haematobium which causes human urogenital schistosomiasis. The genome was assembled from PacBio HiFi long reads obtained from a single highly inbred B. ugandae snail, resulting in 356 scaffolds and a haploid genome size of 1.19 Gb (N50 = 6.86 Mb; Benchmarking Universal Single-Copy Orthologs (BUSCO) score = 99.1%). Genome annotation revealed 29,233 protein-coding genes, 1,620 tRNAs, 381 rRNAs, 17 miRNAs, and repetitive elements comprising 49.08% of the genome. Analyses of collinearity blocks and synonymous substitution rates (Ks) detected an ancient whole-genome duplication (WGD) signature in the B. ugandae genome. To support genome annotation, provide transcript resources, and gain insights into defense responses to the incompatible parasite S. haematobium, we performed Illumina-based RNA sequencing (RNAseq) on 30 transcriptomes, including 28 from individual snails exposed to the parasite and non-exposed controls, along with two pooled embryo samples. From these data, we assembled 658,623 transcripts (N50 = 2,377 bp; BUSCO score = 95.5%). Differential gene expression analyses revealed a limited number of genes activated in this incompatible model (B. ugandae - S. haematobium) compared to the compatible model (B. truncatus - S. haematobium) that we previously reported. However, some immune genes, including fibrinogen-related domain containing protein (FReD) and C-type lectin genes, were up-regulated in response to parasite invasion. This study provides a high-quality nuclear genome sequence and transcriptomic resources for bulinine snails, particularly B. ugandae, enhancing our understanding of their biology. These resources are valuable for advancing research on bulinine snail-transmitted diseases in human and veterinary medicine, as well as in African freshwater ecosystems.