Long-day photoperiodic requirements for steviol glycosides and gibberellins biosynthesis and bio-sweetener levels optimization in Stevia rebaudiana Bertoni

Stevia rebaudiana, as a short-day perennial, produces steviol glycoside (StGlys) metabolites recognized as healthy natural sweeteners, ca. 300 times sweeter than sucrose, being stevioside (ST) and rebaudioside A (Reb-A), the main StGlys for the natural sweetener demanding industries. Nevertheless, discussions persist regarding the ideal light regimen and respective StGlys biosynthesis regulation in S. rebaudiana aimed at enhancing and optimizing the StGlys large-scale production for industrial purposes. The present work reports on the biosynthesis and the contents of StGlys in leaves and stems in different developmental stages of S. rebaudiana plants submitted to different photoperiods. The final contents resulted from the response of genes in the shared StGlys and gib-berellins (GAs) biosynthesis pathway, notably showing differential gene expression patterns in leaves and stems at the different developmental stages. Plants developing under 16/8 h (light/dark) photoperiod increased StGlys contents resulting from the upregulation of S. rebaudiana kaurenoic acid 13-hydroxylase (SrKAH) and uridine diphosphate glycosyltransferase (SrUGTs) genes in association with the downregulation of GAs biosynthesis-related genes in leaves. In contrast, the positive overall regulation of GAs biosynthesis genes in stems appeared as a requirement of GAs for stem elongation and plant growth. Conclusively, the research reports a deeper understanding of transcriptional responses, biosynthesis, and ST and Reb-A yield mechanisms in S. rebaudiana plants under different photoperiodic conditions. Altogether, leading to the potential optimization of commercial production, extraction, and purification while highlighting photoperiodic-responsive StGlys/GAs genes as potential molecular targets for metabolic engineering and future development of superior S. rebaudiana genotypes aiming further large-scale StGlys production and yield to attend the continuous increasing commercial and industrial demand.