De novo transcriptome profiling of mustard aphid (Lipaphis erysimi) and differential expression of transcripts associated with developmental stages, feeding and non-feeding conditions

Lipaphis erysimi is a Brassicaceae specialist aphid, which causes significant losses in yield and/or reduction of oil content of vegetable and oilseed brassicas and is a major pest in the Indian subcontinent. This study reports the de novo transcriptome of L. erysimi for the first time. We also present a comparative analysis of nymphs and adult transcriptomes to study the differential expression profiles associated with different developmental stages as well as different feeding conditions. For this, RNA-seq was performed on three different biological samples adults, nymphs (with all nymph stages pooled) and adults starved for 3 hours (referred to as Adult Feeding, AF; Nymphs Feeding, NF, and Adult Starved_3 hr, ANF samples henceforth). A final transcriptome comprising 52,652 transcripts of 1064bp average length and N50 value of 1806 bp was generated. A total of 27,112 transcripts were annotated with insect proteins from SwissProt, of which 4128 transcripts were components of 165 KEGG pathways. A total of 17,296 transcripts were classified based on their Gene Ontology. Potential transcripts for host selection, detoxification, salivary proteins and effectors, molecular chaperones and developmental genes were identified. A total of 23,532 transcripts that remained unannotated were subjected to BLAST against aphid sequences available at AphidBase and a total of 3091 transcripts had hits with sequences of other aphids in the database, out of which 1380 had protein hits. A total of 20441 found to share no homology to any sequence available in the public domain and could therefore represent novel aphid genes or sequences that are unique to L. erysimi. This is an exploratory study with no biological replicates. However, the significant repertoire of feeding- and development-related genes and their differential expression profiles generated in this study adds to the limited data available on L. erysimi and it would facilitate studies on the molecular basis of aphid feeding and development. This could also allow identification of novel target genes for development of RNAi-based aphid control methods.