Comparative analysis of herbivory responsive miRNAs to delineate pod borer (Helicoverpa armigera) resistance mechanisms in Cajanus cajan and its wild relative Cajanus scarabaeoides.

KEY MESSAGE: Comparative analysis of herbivory responsive miRNAs between pod borer susceptible C. cajan and its resistant Crop Wild Relative (CWR) C. scarabaeoides revealed miRNA-based regulation of defense genes and plant-insect interactions. Gram pod borer (Helicoverpa armigera) is one of most devastating pests of pigeon pea (Cajanus cajan) worldwide, responsible for huge losses in crop productivity. The lack of genes conferring resistance to pod borer in pigeon pea has proven to be a bottleneck for its improvement. One of its CWR, C. scarabaeoides has demonstrated resistance to this pest and can be exploited for developing pest resistant crop varieties. Differences in expression patterns of herbivory responsive microRNAs in the susceptible C. cajan and resistant C. scarabaeoides after different time duration of pod borer infestation (2 h, 8 h and 18 h) were identified, characterized and functionally validated to understand their role in insect defense response. A total of 462 conserved and 449 novel miRNAs and 273 conserved and 185 novel miRNAs, were identified in C. cajan and C. scarabaeoides, respectively. Among the identified miRNAs, 65, 68 and 65 miRNAs were found to be differentially expressing between the C. scarabaeoides and C. cajan libraries 2 h, 8 h and 18 h post infestation, respectively. These miRNAs were found to target genes involved in a number of pathways contributing to defense and acquired resistance in C. scarabaeoides against pod borer, indicating miRNA-based regulation of defense pathways. Expression patterns of eight of these miRNAs were validated by qRT-PCR. This study provides novel insights into the miRNA-mediated plant-insect interactions and the mechanisms of regulatory pathways involved in insect defense. These findings can be utilized for further exploring the mechanism of herbivore defense in plant systems.