Sucrose promotes branch-thorn occurrence of Lycium ruthenicum through dual effects of energy and signal.

This article investigates the molecular and physiological mechanisms underlying the occurrence of visible branch-thorns in Lycium ruthenicum, an eco-economic thorny shrub. Using plants from a single clone that exhibited two phenotypes—thorny branches with more leaves and thornless branches with fewer leaves—microscopic, transcriptomic (RNA-Seq), and biochemical analyses identified that higher sucrose content in apical buds correlates with thorn development, while trehalose-6-phosphate (T6P) content shows an inverse relationship. Key genes involved in starch and sucrose metabolism, including sugar transport protein 13 (SUT13), sucrose synthase (SUS), trehalose-phosphate phosphatase (TPP), and trehalose-phosphate synthase (TPS), were differentially expressed between thorny and thornless branches. Experimental treatments demonstrated that exogenous sucrose promotes thorn occurrence and growth, whereas leaf removal reduces sucrose supply and inhibits thorn development, suggesting sucrose acts both as an energy source and signaling molecule in thorn formation. The study proposes a model where leaf number influences sucrose supply to apical buds, regulating thorn occurrence via modulation of T6P and related gene expression, providing a foundation for breeding thornless L. ruthenicum and related species.