A GmGTF3A-GmSTF1/2 module governs GmPsbS-dependent photoprotection under high-light stress in soybean

Non-photochemical quenching (NPQ) dissipates excess light energy as heat, preventing photosystem damage. PsbS is essential for energy-dependent quenching (qE), but its transcriptional regulation in crops remains unclear. Here, we characterize the functional roles of two PsbS paralogs in soybean and identify a transcriptional regulatory module that governs their expression under high-light stress. We show that GmPsbS1 and GmPsbS2 are predominantly expressed in leaves, exhibit diurnal rhythms, and encode chloroplast-localized proteins. The CRISPR/Cas9-generated double mutant showed strong photoinhibition under high light, with reduced Pn, impaired NPQ, lower photosystem protein levels, higher ROS accumulation, and greater oxidative damage. Using yeast one-hybrid screening, we identified the bZIP transcription factor GmSTF1 as a direct activator of both GmPsbS genes. GmSTF1/2 activate their respective transcriptional expression by directly binding to the TGACGT cis-element located within their promoter regions, and overexpression of GmSTF1 in soybean enhances NPQ, mitigates oxidative stress, and confers improved tolerance to high-light stress. Furthermore, the C2H2 zinc finger protein GmGTF3A physically interacts with GmSTF1/2 and enhances their transcriptional activation of GmPsbS in transient assays, suggesting that it may function as a putative transcriptional co-activator. Collectively, our findings establish GmPsbS as a key photoprotective executor in soybean, with GmSTF1/2 and GmGTF3A cooperatively activating its expression to fine-tune NPQ under high-light stress, offering insights and targets for improving photosynthetic resilience.