Small RNA-seq in response to cotton bollworm in resistant and susceptible soybean

Soybean is one of important oil crops in the world. The defoliating insects including chewing and sucking insects are severely damaging pests for soybean production worldwide. However, until now, the defense mechanism against defoliating insects in soybean remains largely unknown. Cotton bollworm (Helicoverpa armigera) is one of the major chewing insects for soybean. Previously, a wild soybean (Glycine soja), ED059, has been shown to possess a high level of resistance to this pest. In order to understand the possible underlying resistance mechanism, we developed the resistant and susceptible bulks of F2 individuals derived from a cross between ED059 and a susceptible soybean cultivar (cv.) Tianlong 2 and compared the miRNA species in response to cotton bollworm between these two bulks by use of small RNA-seq technology. In total, 423 known and 18 potential novel miRNAs were identified. Sixty-three miRNAs were constitutively expressed in the resistant bulk when compared with the susceptible bulk. Seventy-three and 26 miRNAs were significantly regulated by H. armigera feeding in the susceptible and resistant bulks, respectively. Nineteen miRNAs were specifically regulated by H. armigera in the resistant bulk. Our data suggests that both constitutive and inducible miRNAs may contribute to the resistance to H. armigera in the resistant wild soybean. The analysis of the miRNA targets indicates that multiple pathways may be involved in regulating the resistance, for example, the pathways mediated by calcium-dependent protein kinases (CDPKs), cytochrome P450, ethylene, leucine rich repeat (LRR) receptor serine/threonine kinases. Our findings will contribute to the understanding of soybean responses to defoliating insects, and further studies of these miRNAs and their targets may lead to strategies to control them.