# Transcriptional Analysis of Masson Pine
## 3 Results
### Hormone Regulation under Elevated CO2 Stress  
Based on previous studies [30; 31; 32; 33], combined with KEGG analysis results, the expression patterns of 5 plant hormones (ABA, GA, SA, BR and JA) and their corresponding synthesis genes under CO2 stress were analyzed in this study. In the ABA synthesis pathway, except for the expression of _ZEP_ (zeaxanthin epoxidase) that was slightly up-regulated (no significant difference from CK), all other genes were down-regulated. Among them, _NCED_ (9-cis-epoxycarotenoid dioxygenase) decreased most obviously (Figure 4B). and the log2 fold changes in expression compared to CK decreased 4.73, 6.10 and 5.38 times at 6 h, 12 h and 24 h, respectively. On the other hand, the genes expression pattern of the other four hormones showed an increasing trend under CO2 stress. The key enzyme in the GA metabolic pathway is geranyl geranyl pyrophosphate (GGPS), which catalyzes the synthesis of geranylgeranyl pyrophosphate (GGPP) from isopentenyl  
Figure 3: Influence of high CO2 concentration on sucrose, starch and cell wall components. (**A**) The sucrose, starch and cell wall component biosynthesis pathways according to [PERSON] [28] and [PERSON] [29]. The blue, purple and green rectangles represent the cytosol, chloroplast and Golgi, respectively. The different enzymes are shown in red font. (**B**) Expression changes in the genes involved in metabolic pathways in response to stress. White indicates no change, red up-regulation, and blue down-regulation in each treatment, as shown in the color bar for a log2 fold change scale. The abbreviations in the figure are shown in Table 2 from Appendix A.  
pyrophosphate (IPP), geranyl pyrophosphate (GPP) and farnesyl pyrophosphate (FPP). Under CO\({}_{2}\) stress, _GGPS_ expression increased continuously with time (Figure 4B). As shown in Figure 4A, SA can be synthesized via two routes, by isochorismic acid (ICA) and by cinnamic acid (Ca), benzoic acid (Ba), etc. The specific genes involved in the first pathway have not yet been thoroughly studied [34], while the second pathway has been well researched. Under CO\({}_{2}\) stress, _PAL_ expression continued to increase, reaching a peak at 12 h and then stabilizing (there was no significant difference between 24 h and 12 h). Due to the expression pattern of _PAL_, we speculated that the pathway used for SA synthesis in Masson pine under CO\({}_{2}\) stress was mainly the second pathway. The BR synthesis pathways include early (Figure 4A, yellow block) and advanced (blue block) C-6 synthetic pathways [35]. Intermediate metabolites in the advanced pathway could be converted to corresponding metabolites in the early pathway. However, at the upstream pathway, the conversion efficiency was not very high because the expression levels of _ROT_ (C-23 hydroxylase) was down-regulated with increasing treatment time. In contrast, downstream of the pathway, due to the increase in _CYP_ expression (Figure 4B), BR might be synthesized through the early pathway. Overall, both metabolic pathways showed increased efficiency under CO\({}_{2}\) stress (Figure 4B). All genes in the JA (MeJA) synthetic pathway were up-regulated under CO\({}_{2}\) stress. Among them, _AOC_ (allene oxide synthase) was the most significantly up-regulated. At 6 h, the relative expression level of _AOC_ was 2.84 times that of CK and then increased, and may continue to increase with increased treatment time. Within 24 h, the expression of _AOC_ was far higher than that of the other genes in the pathway (Figure 4B). It could be speculated that _AOC_ might be a key gene involved in the induction of JA production in Masson pine under high CO\({}_{2}\) concentrations. Figure 4: Influence of high CO\({}_{2}\) concentration on hormone and stomatal regulation. (**A**) The hormone biosynthesis pathways and stomatal regulation mechanism according to [PERSON] [35]. The mazarine, green, brown, purple and wathet frame represents ABA, GA, SA, JA and BR synthetic pathways, respectively.