Comparative transcriptomic and metabolomic analyses reveal the protective effects of silicon against low phosphorus stress in tomato plants

Abstract

Phosphorus (P) is an essential nutrient controlling plant growth and development through the regulation of basic metabolic processes. Soil P deficiency is one of the major limiting factors for sustainable crop production worldwide. Previous studies have demonstrated that silicon (Si), as a beneficial element, promotes plant nutrition, growth, development, and responses to low P (LP) stress; however, the molecular mechanisms underlying Si-mediated LP tolerance remain largely unclear. Here, we found that LP + Si treatment increased the net photosynthetic rate and shoot fresh weight by 34.3%, and 121.3%, respectively compared with LP alone. RNA-sequencing and metabolomic analyses were subsequently performed with tomato plants grown under control and P depleted conditions with or without Si amendment. RNA-sequencing showed that Si supply alters not only the expression of genes involved in the metabolism of carbon (C), nitrogen (N), and P but also phosphorylation processes and metabolism of glutathione and reactive active oxygen in tomato roots. Si also affected the expression of genes encoding major transcription factors such as WRKY and MYB under LP stress. Moreover, a set of genes encoding the enzymes or regulators of organic acid (OA) metabolism or secretion were differentially expressed in Si-treated P deficient roots compared with those in LP stress alone. Furthermore, the metabolomic analysis showed that the levels of several OAs were significantly elevated in Si-treated P deficient roots. Taken together, these results indicate that exogenous Si increases the secretion of OAs by modulating C/N metabolism in LP-treated tomato roots and thereby improving plant growth under LP stress.