## 3 Discussion
### Roles of Photosynthesis Genes in Resin Yield  
As one of the by-products of photosynthesis, the resin is a way of carbon fixation in pine trees, so photosynthesis is a crucial physiological process that determines the resin yield [15]. Photosynthesis affects the resin yield in two main aspects, one is whether the photosynthetic products are sufficient for resin biosynthesis, and the other is whether the pine trees can grow vigorously to develop enough resin ducts [55]. Previous studies revealed that the photosynthetic capacity of the high resin-yielding clone is much stronger than that of the low resin-yielding clone, and self-defense measurement can be quickly initiated under strong light and high temperature in high resin yield [16]. In this study, many genes involved in photosynthesis were significantly up-regulated at the transcriptional and proteomic levels. LHCs in PSI and PSII play crucial roles in light harvesting and light protection [56; 57]. Several genes referred to LHCs, such as _Lcha1_, _Lcha3_, _Lchb1_, _Lchb2_, and _Lchb4_, were greatly up-regulated at the transcriptional level, indicating that high resin yield had a stronger capacity for light-harvesting and light protection, which could dissipate excess excitation energy under strong light and maintain efficient photosynthetic capacity under strong light. PSII is a protein complex composed of multiple subunits, and PsbR is  
Figure 8: Heatmap of DEGs and DEPs related to terpenoid biosynthesis (**A**), JA biosynthesis & signaling (**B**). Up- and down-regulated DEGs/DEPs were indicated by red and blue colors, respectively. Nonsignificant genes/proteins were indicated by a gray color. The cells (from left to right) in the heatmap represent the expression change of gene and protein, respectively. The deletion of the cells on the right represents that the protein corresponding to the gene was not detected in the iTRAQ experiment. a small-molecule subunit protein of PSII, which plays an important role in assisting the stable assembly of the PSII core complex and water oxidation [58]. In this study, the _PsbR_ gene was greatly up-regulated both at the mRNA and protein levels. In addition, the PsbS may stabilize the PSII-LHCII supercomplex structure and improve electron transmission efficiency [59], our results showed that the _PsbS_ gene was significantly up-regulated at the proteomic level. ATPD is an F-type ATP synthase present in the chloroplast, which utilizes the transmembrane proton electrochemical gradient formed in electron transport to catalyze the synthesis of ATP from ADP and convert light energy into chemical energy [60]. In the present study, the _ATPD_ gene was notably up-regulated both at the mRNA and protein levels, suggesting that high resin yield had higher ATPase activity and could generate more ATP for the biosynthesis of secondary metabolites. Rubisco (rbcL and rbcS) is a bifunctional enzyme located in the chloroplast stoma and catalyzes photosynthetic CO\({}_{2}\) fixation to form ribulose-1,5-bisphosphate (RuBP) [61], and the transcript levels of _rbcL_ and _rbcS_ could directly reflect the photosynthetic efficiency [62]. In this study, _rbcS_ was up-regulated both at the transcriptional and proteomic levels, and _rbcL_ was up-regulated at the proteomic level, indicating that the up-regulation of the _rbcL_ and _rbcS_ might play a crucial role in resin yield. These results suggested that up-regulation of the Rubisco-related genes in high resin yield enhanced CO\({}_{2}\) assimilation, which played an important role in the production of photosynthetic products from needles and provides a material basis for growth and the biosynthesis of secondary metabolites in masson pine. Chlorophyll is an essential pigment for photosynthesis in green plants and is crucial for light absorption, energy transfer, and photosynthetic charge separation that eventually result in the transfer of an electron from the photosystem to NADP+ and proton-driven ATP production [63].