Novel insights into the molecular mechanisms underlying the resistance of Camellia sinensis to Ectropis oblique provided by strategic transcriptomic comparisons

• Jasmonate/ethylene synthesis and signaling transduction appeared to be particularly active for insect resistance in geometrid-damaged tea plants.
• Most brassinosteroid-related genes were highly expressed, produced positive resistance effects and may have acted synergistically with jasmonate pathways.
• Herbivore-induced plant volatiles (HIPVs), particularly terpenoid volatiles and phenylpropanoid, play an important role in defense responses to tea geometrids.

The tea plant (Camellia sinensis (L.) O. Kuntze) is vulnerable to Ectropis oblique (Prout) (tea geometrids) in warm and humid climates. Therefore, tea plants have generated a series of mechanisms in response to the two stimuli related to E. oblique feeding: mechanical damage and oral secretion stimuli. To elucidate the molecular mechanisms underlying the responses to these distinct inducers, we employed RNA-sequencing (RNA-Seq) to compare three genome-wide expression profiles of a mechanically damaged plant, geometrid-damaged plant and undamaged control.Using the Illumina sequencing platform, we obtained approximately 304.54 million reads in total. These reads were assembled into 65,548 unigenes with an average length of 602 bp and an N50 of 860 bp. By comparing the profiles between the mechanically damaged plant and undamaged control, geometrid-damaged plant and undamaged control and geometrid-damaged plant and mechanically damaged plant, 33,418, 27,029 and 28,260 differentially expressed unigenes were identified, respectively. A comparison of the transcriptomes of the geometrid-damaged and mechanically damaged plants showed that 2995 unigenes were induced only by oral secretion stimuli. These unigenes exhibited significant differences in expression for the jasmonate/ethylene signaling and brassinosteroid pathways, terpenoid synthesis and phenylpropanoid biosynthesis, which are involved in defense against insect pests. Finally, reverse transcription PCR (RT-PCR) was used to verify the expression of preferentially expressed unigenes in the geometrid-damaged plant compared with that of the mechanically damaged plant as predicted by RNA-Seq.Our research yielded novel insights into the molecular mechanisms of pest resistance in tea plants and determined numerous genes and pathways that are involved in these processes. In addition, the expressed sequences were compiled to provide a valuable resource for the study of tea plant resistance to pests.