Elevated CO 2 can stimulate plant growth in greenhouses, but the molecular mechanism behind this response is unclear, especially in eggplants. In this study, we evaluated the physiological and photosynthetic response of the eggplant variety 'Shenyuan 3' under elevated CO 2 , and the candidate genes related to this response were identified by transcriptomic analysis. The results showed that elevated CO 2 can promote eggplant growth and development in greenhouses; plant height and stem diameter were maximally increased by 28.62% and 5.20%, respectively. Net photosynthetic rate, light saturation point and intercellular CO 2 concentration of eggplant leaves increased by 86.11%, 49.94% and 102.06%, respectively, whereas light compensation point, dark breathing rate and stomatal conductance decreased by 35.90%, 27.30% and 26.03%, respectively. A total of 169 differentially expressed genes (DEGs) were screened, of which 99 were up-regulated and 70 were down-regulated. Gene Ontology (GO) function enrichment analysis suggested that these proteins can be classified into 11 molecular functions, including transcription factors, phosphoenolpyruvate carboxylase and oxidoreductase. Pathway analysis indicated that elevated CO 2 affects plant growth and development by affecting carbon metabolism, carbon fixation, chlorophyll and porphyrin metabolism. Twelve genes were further detected by qRT-PCR, and 11 genes showed similar dynamics with the transcriptomic data. Bilirubin dehydrogenase Sme2.5_04464.1_g00001 and the malate dehydrogenase gene Sme2.5_03383.1_g00002, which are involved in the chlorophyll porphyrin pathway and carbon metabolism, respectively, were up-regulated. Transcription factors bHLH (Sme2.5_01232.1_g00025) and GATA (Sme2.5_00372.1_g00006) were also up-regulated under elevated CO 2 treatment. Further research should focus on cloning these genes and identifying their response mechanism under elevated CO 2 .

The increase in the concentration of CO2 in the atmosphere has attracted widespread attention. To explore the effect of elevated CO2 on lettuce growth and better understand the mechanism of elevated CO2 in lettuce cultivation, 3 kinds of lettuce with 4 real leaves were selected and planted in a solar greenhouse. One week later, CO2 was applied from 8:00 a.m. to 10:00 a.m. on sunny days for 30 days. The results showed that the growth potential of lettuce was enhanced under CO2 enrichment. The content of vitamin C and chlorophyll in the three lettuce varieties increased, and the content of nitrate nitrogen decreased. The light saturation point and net photosynthetic rate of leaves increased, and the light compensation point decreased. Transcriptome analysis showed that there were 217 differentially expressed genes (DEGs) shared by the three varieties, among which 166 were upregulated, 44 were downregulated, and 7 DEGs were inconsistent in the three materials. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that these DEGs involved mainly the ethylene signaling pathway, jasmonic acid signaling pathway, porphyrin and chlorophyll metabolism pathway, starch and sucrose metabolism pathway, etc. Forty-one DEGs in response to CO2 enrichment were screened out by Gene Ontology (GO) analysis, and the biological processes involved were consistent with KEGG analysis. which suggested that the growth and nutritional quality of lettuce could be improved by increasing the enzyme activity and gene expression levels of photosynthesis, hormone signaling and carbohydrate metabolism. The results laid a theoretical foundation for lettuce cultivation in solar greenhouses and the application of CO2 fertilization technology.