Induction of secondary cell wall biosynthesis genes and their regulators by melatonin in Glycine max

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 for the regulation of plant growth and development. In this study, we demonstrated that the exogenous treatment of melatonin to Glycine max significantly enhanced plant lateral growth by increasing stem diameter. In addition to the stem thickness, secondary cell wall (SCW) deposition acts as another critical factor for stem rigidity for lodging resistance. To understand whether exogenous treatment of melatonin would regulate SCW biosynthesis genes, we performed transcriptomic analyses on the stems of Glycine max with or without melatonin treatment. Through the differentially-expressed-genes (DEGs) analyses, many SCW biosynthesis genes were found to be regulated by melatonin, including the cellulose, hemicellulose and lignin biosynthesis enzymes. We also found that the two known master regulators, NAC and MYB, of SCW biosynthesis genes were induced under melatonin treatment, which further supported our observation on the differential expression of SCW biosynthesis genes. Our study highlighted the improvement of lodging resistance by the exogenous treatment of melatonin through the increase of plant stem thickness and the regulation of SCW biosynthesis genes and their upstream TFs in Glycine max.