Stress-responsive sucrose synthase gene, DoSUS2, improves soluble sugar accumulation in Dendrobium officinale

Dendrobium officinale (D. officinale), particularly the Danxia cultivar, thrived in harsh environments characterized by intense summer heat and limited rainfall, conditions that promoted the substantial accumulation of bioactive polysaccharides. Sucrose synthase (SUS), which played an indispensable role in modulating sucrose metabolism and catabolism, was crucial for plant stress resistance; however, its function in the stress adaptation of D. officinale remained poorly understood. In this study, we demonstrated that abiotic stress enhanced the accumulation of soluble sugars by inducing the transcriptional activation of SUS genes in D. officinale (referred to as DoSUS). Four DoSUS genes were identified and characterized, and their classification into three distinct subclasses (SUS I, SUS Ⅱ, and SUS III) suggested diverse functional roles. Among them, DoSUS2 exhibited a tissue-specific expression pattern and a marked response to drought stress and exogenous abscisic acid (ABA) treatment. Heterologous expression of DoSUS2 in Arabidopsis thaliana significantly improved drought and ABA tolerance, enhanced soluble sugar accumulation, and increased reactive oxygen species (ROS) scavenging capacity. Furthermore, the transcription factor DobHLH14 was found to directly bind to the E-box motif in the DoSUS2 promoter, potentially contributing to a saccharometabolism regulatory network involving DoSUS2, DoSUS1, DoGT5, DoUGE2, DoUGE3, and DoVIN2. Collectively, these findings delineated a mechanistic model in which DoSUS2 modulated saccharometabolism to enhance stress tolerance in D. officinale. This study advanced our understanding of the molecular basis of drought adaptive and provided a theoretical foundation for breeding high-polysaccharide D. officinale varieties suited to arid environments. Moreover, the identified DobHLH14-DoSUS2 module represented a promising genetic target for simultaneously improving stress tolerance and polysaccharide yield.