Analysis of genes related to chlorophyll metabolism under elevated CO2 in cucumber (Cucumis sativus L.)

Abstract

Cucumber is a vegetable crop with a large area of protected cultivation. The application of CO2 can promote photosynthesis in cucumber and increase yield. However, as an important photosynthetic pigment, and the molecular mechanisms of chlorophyll action are still unclear. It is therefore of great theoretical and practical significance to discover CO2-sensitive genes and analyze metabolic pathways to clarify the mechanisms of promoting photosynthesis by RNA sequencing. In this study, the photosynthetic correlation index and chlorophyll content under elevated CO2 and control conditions were compared. It was found that the application of CO2 expanded the effective light utilization range and promoted the biosynthesis of chlorophyll in cucumber. Seventeen genes related to chlorophyll were discovered in 380 differentially expressed genes (DEGs) obtained by RNA-Seq and they were involved in chlorophyll biosynthesis, chlorophyll-binding protein and chloroplast development. These genes were suggested to be related to increasing photosynthetic rate under enriched CO2 in cucumber. With fold change (FC) > 1.5 at false discovery rate (FDR) <0.05 as the selection criteria, the key enzymes in the chlorophyll metabolism pathway were analyzed, and expression of Csa4G165920 and Csa4G056670 encoding two enzymes were corresponded to the chlorophyll content, indicating that these two genes are also directly involved in chlorophyll metabolism and photosynthesis. These results clarified the molecular mechanism of increased photosynthetic rate caused by increased chlorophyll content and thus which increased carbon source after CO2 enrichment, which laid a foundation for further research on molecular mechanism of CO2 fertilization in cucumber.