Transcriptome and metabolome analysis reveals mechanism of light intensity modulating iridoids biosynthesis in Gentiana macrophylla Pall.

Abstract

Abstract Light intensity is a key factor affecting the synthesis of secondary metabolites in plants. However, the response mechanism of metabolites and genes in G. macrophylla under different light intensities have not been determined. In the present study, G. macrophylla seedlings were treated with LED light intensities at 15 µmol/m2/s (low light, LL), 90 µmol/m2/s (medium light, ML) and 200 µmol/m2/s (high light, HL), and the leaves were collected at 5-day for further investigation. A total of 2162 metabolites were detected, in which, the abundant metabolites were identified as flavonoids, carbohydrates, terpenoids and amino acids. A total of 3313 and 613 differential expression genes (DEGs) were identified after HL and LL groups, respectively, compared to the ML group, enriched in KEGG pathways such as carotenoid biosynthesis, carbon metabolism, glycolysis/gluconeogenesis, amino acids biosynthesis, plant MAPK pathway and plant hormone signaling. In which, the transcription factors GmMYB5 and GmbHLH20 were found to be significantly correlated with loganic acid biosynthesis; the expression of photosystem-related enzyme genes was changed under different light intensities, regulating the expression of enzyme genes involved in the carotenoid, chlorophyll, glycolysis and amino acids pathway and thus affecting their metabolic biosynthesis. As a result, low light inhibited photosynthesis, thus, delaying glycolysis, accumulating certain amino acids and decreasing loganic acid production, while high light got an opposite trend. Our research contributed significantly to understanding the molecular mechanism of light intensity in controlling metabolic accumulation in G. macrophylla.