Insect herbivory time-course reveals unique temporal transcriptomic responses in resistant and susceptible grapevines

Grapevine (Vitis) is a crop of global importance. Insect pests, such as Popillia japonica (Japanese beetle), threaten yields of this high value crop. Vitis labrusca (accession 'GREM4') exhibits the highly-advantageous trait of resistance to Japanese beetles while Vitis vinifera is susceptible (cultivar 'PN40024'). Herein, we undertook an insect herbivory time-course transcriptomic study to identify gene expression differences, and associated processes and pathways, which differ, both temporally and spatially, between 'GREM4' and 'PN40024' under insect herbivory. Upon herbivory, the number of significantly differentially expressed genes (DEGs) increased over time in 'GREM4' but decreased in 'PN40024'. 'GREM4' exhibited greater defense gene enrichment after 4h of herbivory compared to 30min, conversely, 'PN40024' exhibited a greater 30min response which diminished by 4h. In systemic leaves, 'GREM4' exhibited 10x more DEGs than 'PN40024'. Across herbivory and systemic responses, genes associated with insect herbivory defense, including flavonoids, phenylpropanoids, acyltransferases, and signaling-pathways, were implicated in greater numbers, or exclusively, in 'GREM4' compared to 'PN40024' and likely impact insect resistance. Our findings provide insight into the genetic variation, processes, and pathways which underly insect herbivory resistance in Vitis. We report candidate genes and biological pathways for future functional studies and breeding initiatives to advance cultivar development and yields.