Although the regulatory function of miRNAs and their targets have been characterized in model plants, a possible underlying role in the cotton response to herbivore infestation has not been determined. To investigate this, we performed small RNA and degradome sequencing between resistant and susceptible cotton cultivar following infestation with the generalist herbivore whitefly. In total, 260 miRNA families and 241 targets were identified. Quantitative-PCR analysis revealed that several miRNAs and their corresponding targets exhibited dynamic spatio-temporal expression patterns. Moreover, 17 miRNA precursors were generated from 29 long intergenic non-coding RNA (lincRNA) transcripts. Genome-wide analysis also led to the identification of 85 phased small interfering RNA (phasiRNA) loci. Among these, nine PHAS genes were triggered by miR167, miR390, miR482a, and two novel miRNAs, including those encoding a leucine-rich repeat (LRR) disease resistance protein, an auxin response factor (ARF) and MYB transcription factors. Through combined modeling and experimental data, we explored and expanded the miR390-tasiARF cascade during the cotton response to whitefly. Virus-induced gene silencing (VIGS) of ARF8 in whitefly-resistant cotton plants increased auxin and jasmonic acid (JA) accumulation, resulting in an increased tolerance to whitefly infestation. These results highlight the provides a useful transcriptomic resource for plant-herbivore interaction.

Cotton is one of the most important economic crops in the world, whereas insect attacks is a prime cause of its losses on yield and quality. Despite it is important, little is known about the mechanism of cotton response to insect. In this study, we simulated insect feeding by applying insect oral secretions (OS) to wounds, and combined transcriptome and metabolome analysis to comprehensively investigate how OS from two major pest species (Helicoverpa armigera and Spodoptera litura) affect cotton defense responses. Obvious differences were observed that 12,668 and 13,379 genes differently expressed respectively in cotton after being treated with different OS when compared with wounding along. Upon the addition of OS, JA-signaling pathway were rapidly and strongly induced, however SA-biosynthesis related gens were significantly down-regulated. By constructing the co-expression gene network, we identified a hub gene which encoding a leucine-rich repeat receptor kinase may play important role in recognition and signal transduction at early stage. We also found that OS from different insect species altered abundance of flavonoid related compound with different patterns. Interestingly, Gossypol which is a well-known anti-insect compound was kept a relative low content after OS application relative to wounding which implied the existence of the suppression effects of OS to cotton defense response. This study illustrated the transcriptional and metabolic changes of cotton in responding to OS from two chewing insect species, identified potential key gene during the interaction process and finds the evidence for OS’s inhibition effects on cotton defense response.