Melatonin-mediated protection of photosynthetic attributes in Cyphomandra betacea Sendt. seedlings under selenium stress

Cyphomandra betacea Sendt. is a typical non-selenium (Se) hyperaccumulator, the plant growth is inhibited in high Se-contaminated soils. This study investigated the salutary effect of melatonin (MT) in alleviating Se stress (0.1 mg L −1 Na 2 SeO 3 treatment) and enhancing Se uptake in C. betacea seedlings. MT application enhanced the seedlings biomass and antioxidant enzyme activities of C. betacea under Se stress. Transcriptomic analysis revealed that Se stress suppressed the expression of photosynthesis-related genes while upregulating flavonoid biosynthesis-related genes in C. betacea leaves. MT application induced transcriptional reprogramming under Se stress. These differentially expressed genes were primarily enriched in the pathways of photosynthesis and photosynthesis-antenna proteins. Furthermore, MT upregulated the expression of genes associated with porphyrin metabolism and carbon fixation pathways, suggesting that MT restored photochemical homeostasis under Se stress, by improving electron transport rate, light conversion efficiency, and promoting carbon assimilation, to ensure normal growth of C. betacea seedlings under Se stress. Notably, MT application enhanced Se uptake, upregulating the Se/S transporters ( SULTR3;1 , SULTR4;2 ) and Se assimilation-related genes ( SiR , CBL ) transcription. Overall, these results provide new insights into the probable mechanism underlying MT-mediated protection of photosynthesis and promoted Se accumulation, and facilitated the implementation of plant Se biofortification strategies. • Selenium (Se) stress affects biochemical and gene transcription of C. betacea . • Physiological/transcriptomic aspects are disturbed by Se toxicity. • Melatonin (MT) alleviates the growth penalty of C. betacea under Se stress. • MT recovered photosynthetic attributes of C. betacea under Se stress. • MT promotes Se uptake, transport, and accumulation.