The impact of high-light stress on the physiology and transcriptome of Pterocladiella capillacea

Pterocladiella capillacea, a subtropical red alga rich in bioactive compounds, holds significant pharmaceutical value and is widely distributed in intertidal and subtidal rocky reefs. However, the natural biomass of this species declines due to climate change and anthropogenic activities, posing challenges to its aquaculture and commercial exploitation. High-light stress represents a critical environmental factor affecting its growth and reproduction, yet the underlying molecular mechanisms remain poorly understood. This study investigates the effects of high-light stress on chlorophyll fluorescence parameters, physiological indices, and transcriptomic profiles of P. capillacea collected from Naozhou Island, Zhanjiang. Results reveal that high-light stress significantly perturbs chlorophyll fluorescence parameters, photosynthetic rates, photosynthetic pigment biosynthesis, malondialdehyde content, antioxidant enzyme activities, and osmolyte accumulation. The transcriptomic analysis identifies 2,281, 7,640, and 8800 differentially expressed genes (DEGs) under 120 μmol m⁻²s⁻¹, 300 μmol m⁻²s⁻¹, and 500 μmol m⁻²s⁻¹ treatments, respectively. Functional enrichment analysis (GO and KEGG) highlighted DEGs primarily involved in photosynthesis, antioxidant systems, sucrose/starch metabolism, and chlorophyll biosynthesis. Temporal expression pattern analysis further uncovered five distinct gene expression trends associated with increasing light intensity. These findings provide novel insights into the physiological and molecular mechanisms underlying high-light tolerance in P. capillacea, offering a theoretical foundation for future molecular breeding programs to improve stress resilience in this economically important alga.