Exogenous application of melatonin activates secondary cell wall biosynthetic genes and increases stem thickness in Glycine max

Abstract Plant lodging severely reduced crop yield and quality. Different plant growth regulators (PGRs) have been applied to improve lodging resistance through the regulation of physiological changes, especially on the increase of stem thickness and strength. Melatonin is a pleiotropic PGR to regulate plant growth and development. In this study, we demonstrated that the exogenous treatment of melatonin to Glycine max significantly enhances plant lateral growth by increasing stem diameter. Beside stem thickness, secondary cell wall (SCW) deposition may contribute to stem rigidity to improve the lodging resistance. To understand whether melatonin regulates the genes relevant to SCW deposition, we performed transcriptomic analysis on the stems of Glycine max with or without melatonin treatment. Through the differentially expressed genes (DEGs) analysis, many SCW biosynthetic genes were found to be regulated by melatonin, including the cellulose, hemicellulose and lignin biosynthetic enzymes. These SCW biosynthetic genes are governed by a hierarchical regulatory network and mainly regulated by two transcription factor (TF) families, NAC and MYB. The results showed that the gene expression of these NAC and MYB were induced by melatonin. Our study highlighted that the exogenous treatment of melatonin could improve the lodging resistance through the increase of plant stem thickness and the regulation of SCW biosynthetic genes and their upstream TFs in Glycine max.