Expression of Genes in New Sprouts of Cunninghamia lanceolata Grown Under Dark and Light Conditions

Abstract

Chinese fir (Cunninghamia lanceolata) cotyledons are green in darkness due to the coexistence of functional dark-operative protochlorophyllide reductase (DPOR) and light-dependent protochlorophyllide reductase (LPOR). In this study, we found that the POR gene for LPOR and the ChlB, ChlL, and ChlN genes for three DPOR subunits were strongly downregulated in dark-grown new sprouts in which chlorophyll biosynthesis was inhibited. We extracted, sequenced, and annotated the total RNA from etiolated (dark-grown) and green (light-grown) sprouts. A total of 70,499 unigenes were found, of which 47,410 were annotated. Among them, 3263 differentially expressed genes were identified between dark- and light-grown samples. According to the Kyoto Encyclopedia of Genes and Genomes databases, the five most affected metabolic pathways were flavonoid biosynthesis, photosynthesis-antenna proteins, photosynthesis, cutin, suberine and wax biosynthesis and stilbenoid, diarylheptanoid, and gingerol biosynthesis. Based on the acquired cDNA sequences, we applied quantitative PCR to further analyze the relative expression levels of 18 nuclear genes and 11 chloroplast genes related to photophosphorylation. Both transcriptomic and quantitative PCR results indicated that dark treatment can significantly block the expression of all of the identified genes related to the protein complexes of photosynthetic electron flow in new sprouts. Dark treatment of new sprouts of Chinese fir caused etiolation via blockage of the expression of DPOR- and LPOR-encoding genes. Both nuclear and plastid genomic genes related to photosynthesis were significantly downregulated in etiolated sprouts. The results provide new clues to understanding the different mechanisms of chloroplast development in different photosynthetic organs.