SlMYBS3L-SlERF.E4-SlGGP1 mediates the accumulation of ascorbic acid in tomato promoted by organic nutrient solution

Ascorbic acid (AsA) is a crucial antioxidant for both human health and plant stress resistance. Organic cultivation practices are known to enhance ascorbic acid (AsA) accumulation in fruits; however, the underlying molecular mechanisms remain poorly understood. Here, we show that treatment with an organic nutrient solution (OR) significantly boosted the AsA content in tomato fruits. We identified an ethylene response factor, SlERF.E4, as a key positive regulator of OR-induced AsA biosynthesis. SlERF.E4 directly binds to the DRE motif in the promoter of SlGGP1, a rate-limiting gene in the AsA biosynthetic pathway, and activates its transcription. Further research found that an upstream R2R3-type transcription factor, SlMYBS3L, acts as a "braking component" for AsA synthesis under conventional inorganic cultivation conditions. On one hand, SlMYBS3L suppresses the transcription of the AsA synthesis activator SlERF.E4; on the other hand, it directly inhibits the expression of the AsA synthesis gene SlGGP1. OR treatment downregulates the expression of SlMYBS3L, thereby synchronously releasing these two layers of inhibition, activating the SlERF.E4-SlGGP1 module, and consequently leading to a synergistic enhancement of AsA biosynthesis. This study systematically elucidates the role of the SlMYBS3L-SlERF.E4-SlGGP1 module in the organic nutrient signaling pathway. It not only clarifies the mechanism by which organic cultivation improves fruit quality but also provides key gene resources for the molecular breeding of high-vitamin C tomatoes.