## 4 Discussion
### Enriched Biochemical Pathways After C. pepo Eliciation by R. sachalinensis Extract
Five pathways (group 3) were found to be enriched in this comparison only. Pyruvate is a product of glycolysis, a catabolic biochemical process categorized as part of the primary metabolism. The activation of primary metabolism to meet energy demands in plant defense against pathogens has been previously reported [84, 85]. In the enriched pathway, four enzymes were represented, including a dehydrogenase and a pyruvate kinase, both of which were highly up-regulated (more than 4-fold). Under the hypothesis of a rapid response of RS-primed _C. pepo_ plants to _P. xanthii_ infection, it is likely that the increased energy demands lead to the activation of primary metabolism pathways in RSPX-treated plants. Three additional pathways related to \"Monobactam\", \"Cofactors\", and \"Fatty acid\" biosynthesis, are represented by a total of 13 DEPs. Monobactam is a commonly-used antibiotic against bacteria, and its biosynthesis pathway has been related to antifungal activities [86, 87]. The \"Biosynthesis of cofactors\" pathway includes two inositol monophosphatase-like enzymes and two thiamine thiazol synthases (TTSs). The former is an enzyme involved in the metabolism of inositol, a molecule shown to act as a second messenger for various plant responses [88, 89]. The latter is an enzyme involved in thiamin metabolism. TTS was present in the relevant pathway which appeared significantly enriched (groups 4 and 9) in four out of six treatment comparisons and was shown to be related to the PX-induced plant responses, as discussed previously. The role of fatty acids as signaling molecules was previously noted in the context of the \"Fatty acid degradation\" pathway. However, further experiments are needed to validate their roles, both as degraded and newly synthesized products, in PX- and RS-mediated plant responses. Enriched Biochemical Pathways Activated as Common Response Mechanisms or Revealing Further Differences Between Treated Groups  
Several metabolic pathways (groups 4-6) were found to be common across the three treatments versus Control comparisons, suggesting that RS mimics PX in inducing _C. pepo_ responses (groups 5 and 6) or that PX-induced effects are dominant regardless of RS treatment (group 4). Regarding group 4 pathways, glutathione, along with reactive oxygen species (ROS) play important roles in the activation of plant resistance during biotic stress, mainly through the hypersensitive response [90, 91, 92, 93, 94]. Ascorbate has been shown to form part of a complex network for modulating basal and induced plant resistance to pathogens via defense-hormonal signaling and NPR1-dependent induction of defense genes' expression. Furthermore, its production was shown to be activated by applications of various elicitors [95, 96, 97]. Thiamine (vitamin B1) has been reported to activate plant resistance against _Sclerotinia scleroium_, _Plasmopara viticola_, and _Rhizoctonia solani_ by modulating several key regulators of NADPH oxidase, HR-like cell death responses and the phenylpropanol pathway [98; 99; 100; 101; 102; 103]. Furthermore, in arabidopsis plants, thiamine-induced priming was shown to be dependent on hydrogen peroxide and the NPR1 gene [104]. Our previous findings on NPR1-related gene expression in _C. pepo_ plants following _P. xanthii_ infection, and their regulation through defense-related hormones [30], align with the proposed roles of ascorbate and thiamine in NPR1-dependent up-regulation of defense genes in PX-infected plants. Regarding the comparisons between different treatments, the thiamine metabolism pathway is also found enriched in the RS vs. PX and RSPX vs. RS cases, deductively suggesting a pivotal role in pathogen-induced C. pepo responses. Of the four pathways reported in the RSPX vs. PX comparison, the \"Polycomb repressive complex\" stands out, as it is composed of proteins that epigenetically repress gene expression.