Transcriptomic analysis of a compatible tobacco-herbivore interaction and the role of jasmonoyl-L-isoleucine hydrolase 1 in response to growth/defense trade-off

Tobacco (Nicotiana tabacum), an allotetraploid species extensively cultivated worldwide, serves as a key model system for plant research but exhibits high susceptibility to insect pests. The comprehensive molecular mechanisms underlying N. tabacum's response to insect pests remain poorly characterized. In this study, we collected leaf RNA-seq samples from tobacco plants at 0, 6, and 24 h after exposing them to either the aphid (Myzus persicae) or the cotton bollworm (Helicoverpa armigera). The numbers of differentially expressed genes (DEGs) responding to cotton bollworms exceeded those responding to aphids at both 6 and 24 h. Pathway enrichment analysis, weighted gene co-expression network analysis (WGCNA), and clustered expression pattern analysis revealed that the most significantly enriched pathways were involved in hormone signal transduction, secondary metabolism, and the regulation of transcription factors. We employed CRISPR/Cas9 technology to disrupt Jasmonoyl-L-isoleucine hydrolase 1 (JIH1), which was significantly upregulated following insect treatment as confirmed by both RNA-seq and qRT-PCR analyses, to validate its role in insect resistance. The weight of cotton bollworms decreased by 25.67% when feeding on ntjih1-1 plants compared to wild-type (WT) plants. In ntjih1-1 plants, transcripts involved in jasmonic acid (JA), salicylic acid (SA), and ethylene (ET) signaling pathways were activated. Concurrently, plant height decreased, whereas primary root length increased. Interestingly, the expression levels of 13 of 15 JAZ genes were repressed in ntjih1-1 plants. The ntjih1-2 plants showed no enhanced resistance to cotton bollworms, potentially due to functional selective evolution of NtJIH1-1 and NtJIH1-2 during tobacco chromosome doubling. Our results indicate that JIH1 may play a vital role in balancing growth and defense in the plant's immune response to herbivory.