Physiological and molecular insights into color variation and light intensity adaptation in Eucheuma perplexum with applications for selective cultivation

Red algae exhibit remarkable color diversity. However, the physiological and molecular mechanisms driving these color variations remain incompletely elucidated. This study elucidates the physiological and molecular mechanisms underlying color variation in Eucheuma perplexum, with a focus on the red and green morphotypes observed during cultivation. Our research revealed significant differences in pigment content, growth rate, and carrageenan yield between the two morphotypes. Notably, the green morphotype exhibited lower phycoerythrin (PE) content compared to the red morphotype, directly contributing to the observed color differences. RNA-seq analysis revealed significant differential expression of genes, particularly those involved in photosynthesis. Light intensity experiments demonstrated that increased illumination induced phycobiliprotein restructuring, characterized by a pronounced reduction in PE content and significant upregulation of photosynthesis-related genes. These findings indicate that the color variation in E. perplexum is closely linked to adaptation to light intensity, with the green morphotype employing distinct strategies to manage light-induced stress, including increased phenolic compound production and reorganization of photosynthetic pigments. This study provides novel molecular insights into the mechanisms driving color variation in red algae and underscores the potential for selectively cultivating specific morphotypes to optimize production for targeted applications, such as enhancing carrageenan yield or tailoring pigment composition.