Upregulation of ADCS and ALP and Increased pABA Supply Underlie Salicylic Acid-Induced Folate Accumulation in Spinach

Salicylic acid (SA) is an important signaling molecule that regulates plant primary and secondary metabolites accumulation. Although SA has been shown to promote folate accumulation, the underlying mechanism remains unclear. In this study, the effect of SA on folate biosynthesis in spinach (Spinacia oleracea L.) and its regulatory mechanisms were investigated. Physiological and metabolomic analyses showed that foliar SA application increased the contents of folate, soluble protein, and soluble sugar and the abundance of 5-methyltetrahydrofolate, p-aminobenzoate (pABA), and Trp, while the abundance of Ser decreased. The expression of aminodeoxychorismate synthase (ADCS) and alkaline phosphatase (ALP) genes in the folate biosynthesis pathway was upregulated, while the expression of five genes in the folate interconversion pathway and two genes in the Phe/Tyr synthesis pathway was downregulated. Fifty-one transcription factors (TFs) showed expression patterns correlated with those of ADCS and ALP and were predicted to bind to their promoter regions. SA upregulated many hormone genes, and 12 of these correlated strongly with both ADCS and ALP. Moreover, transgenic Arabidopsis lines overexpressing SoADCS constitutively displayed higher folate content in leaves. Taken together, our results suggested that SA may promote folate accumulation by enhancing folate precursor supply, and several candidate TFs and hormone-related genes that may be involved in the regulation of this pathway warrant further study.