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Novel alternative splicing events were identified from BmNPV-susceptible and -resistant silkworm strains after BmNPV infection using high-throughput RNA-sequencing strategy. In total, 12.82 Gb clean RNA-seq data were generated for the two midgut samples from BmNPV-susceptible and -resistant silkworm strains, and 14.78 Gb clean data for the two fat body samples. The number of alternative splicing events and isoforms in the BmNPV-susceptible silkworm strain was more than that in the BmNPV-resistant silkworm strain. Furthermore, alternative splicing genes uniquely present in BmNPV-resistant silkworm strain were involved in functions about ribosome, whereas, alternative splicing genes uniquely present in BmNPV-susceptible silkworm strain were implicated in functions like DNA helicase activity and signal transduction. Additionally, 33 expressed SR or SR-like proteins were identified, and three genes encoding SR or SR-like proteins (tetratricopeptide repeat protein 14 homolog, ubiquitin carboxyl-terminal hydrolase 32and zinc finger CCCH domain-containing protein 18) have a higher number of different alternative splicing events between two silkworm strains. The present study suggested BmNPV treatment may have a smaller effect on the mRNA transcription in BmNPV-resistant silkworms than that in BmNPV-susceptible silkworms, and functions of alternative splicing genes are different between the two silkworm strains.

Intersimple sequence repeat (ISSR) amplification was used to analyze genetic relationships among silkworm, Bombyx mori L., strains. Nineteen primers containing simple sequence repeat (SSR) motifs were tested for amplification on a panel of 42 strains, representative of the diversity of silkworm germplasm; 12 of the primers amplified distinct, reproducible bands. The primers amplified a total of 108 bands, of which 85 (78.7%) were polymorphic. The ISSR results suggested that within the dinucleotide class, the poly(CA) motif was more common than the poly(CT) motif. The ISSR amplification pattern was used to group the silkworm strains into seven subclusters based on their origin in an unweighted pair-group method with arithmetic average cluster analysis by using Nei’s genetic distance. Seven major ecotypic silkworm groups were analyzed. Principal component analysis of the ISSR data supported the unweighted pair-group method with arithmetic average clustering. Therefore, ISSR amplification is a valuable method for determining genetic variability among silkworm varieties. This efficient genetic fingerprinting technique should be useful for characterizing the large numbers of silkworm strains held in national and international germplasm centers.