Identification of candidate genes associated with photosynthesis in eggplant under elevated CO₂

Elevated CO₂ 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 CO₂, and the candidate genes related to this response were identified by transcriptomic analysis. The results showed that elevated CO₂ 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 CO₂ 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 CO₂ 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 <i>Sme2.5_04464.1_g00001</i> and the malate dehydrogenase gene <i>Sme2.5_03383.1_g00002</i>, which are involved in the chlorophyll porphyrin pathway and carbon metabolism, respectively, were up-regulated. Transcription factors <i>bHLH</i> (<i>Sme2.5_01232.1_g00025</i>) and GATA (<i>Sme2.5_00372.1_g00006</i>) were also up-regulated under elevated CO₂ treatment. Further research should focus on cloning these genes and identifying their response mechanism under elevated CO₂.