## 3 Discussion  
The sycamore lace bug, _C. ciliata_, is an important insect pest that has been causing damage to _P. acerifolia_ trees in recent years [2]. _C. ciliata_ usually feeds on the undersides of _P. acerifolia_ leaves, and the leaves develop white spots at the beginning of feeding at the upper side that can cause the leaves to appear chlorotic. The damage caused by this insect pest can reduce leaf photosynthesis, leading to a decline in some physiological and biochemical indexes such as leaf photosynthetic rate, stomatal conductance, transpiration rate, chloroplast pigments and soluble sugars. _C. ciliata_ can only complete its life cycle on the sycamore plant. Based on the importance of the host plant and the limited host specificity of this pest, studying the molecular mechanisms behind the _P. acerifolia_- _C. ciliata_ interaction is important for understanding the expression of resistance in _Platanus_ species to this insect pest. By analyzing gene expression profiles at two different time points, we identified 1907 and 921 unigenes that were significantly up-regulated after 24 and 48 h of feeding, respectively. Previous studies have shown that insect stress can induce massive changes at the transcriptional level in some plants [10; 11; 12]. These changes can reprogram primary and secondary metabolic pathways, activating defense genes and signaling pathways to respond to insect attack. The large number of genes that showed changes in expression in our transcriptome are consistent with these findings. The results of our study establish a signature for _C. ciliata_-induced changes to the leaf transcriptome of _P. acerifolia_. A total of 303 genes were up-regulated in leaves after both 24 and 48 h of _C. ciliata_ feeding. These 303 genes are the key core genes expressed during the interaction between _P. acerifolia_ and _C. ciliata_. Combining the GO, KEGG enrichment analysis, and MapMan results, we speculated that JA-related pathways and terpen play an important role in this plant-insect interaction system. The plant hormone JA plays vital roles in regulating the plant response to various insect stresses [13]. In our experiments, JA-related genes were induced in response to _C. ciliata_ feeding damage. This indicates that in _P. acerifolia_, JA signal transduction may act through a mechanism similar to that in other plants. At the same time, in addition to JA pathway-related genes, we also identified related functional genes, especially genes that encode peroxididases and a series of transcription factors. The identification of these genes will provide the basis for the subsequent development of insect-resistant _Platanus_ trees through genetic screening and possibly through genetic transformation. The controlled production of plant volatiles plays an important role in the indirect plant defense response against insects [13]. Following pest damage, plants will release a series of volatiles, such as terpen, to repel the insect pests and attract natural enemies, thereby improving their insect resistance to protect themselves [7]. In our previous study, we evaluated the types and contents of volatiles in leaves of _P. acerifolia_ damaged by _C. ciliata_[6]. Four chemicals, including cis-3-hexen-l-ol, 1,8-cineole,  
Figure 6: Correlation analysis between gene expression values obtained from RNA-seq and qRT-PCR. The value of qRT-PCR (x-axis) were plotted against RNA-seq values (y-axis). (\(E\))-4,8-dimethyl-1, 3,7-nonatriene, and trans-\(\beta\)-caryophyllene were detected in undamaged leaves. In addition, another five chemicals, \(\alpha\)-thujene, sabinene, myrcene, cis-3-hexenyl acetate, and \(\gamma\)-terpinene, were induced in leaves after feeding by _C. ciliata_. Among these volatile chemicals, cis-3-hexen-1-ol and 1,8-cineole were found to significantly attract _C. ciliata_, whereas trans- \(\beta\)-caryophyllene repelled this insect pest [14]. Our study further identified 14 genes involved in the biosynthesis of these compounds.