Morphological, physiological and genetic analysis of a spontaneous green mutant in Pyropia yezoensis

Color is an important trait that determines the nutritional quality and commercial value of Pyropia yezoensis . In this study, we identified a spontaneous mutant with green-colored blades, designated as RG. To characterize this mutant, we systematically investigated its morphological traits, growth performance, pigment composition, and photosynthetic efficiency. Compared with the wild-type strain (RZ), the green mutant RG exhibited slower growth and delayed maturation. Phycoerythrin (PE) content was significantly reduced in the green mutant RG, suggesting that the green coloration primarily results from decreased PE levels. Chlorophyll fluorescence analysis revealed decreased Φ PSII and qP values but increased NPQ in the green mutant RG. Genetic analysis indicated that the green phenotype is genetically stable and controlled by a recessive nuclear locus. Using a modified QTL-seq approach, we mapped two candidate loci on chromosome PY_1 (spanning 2.45 Mb) associated with the green phenotype. Within these genomic regions, one gene harboring nonsynonymous mutations was prioritized as a candidate causal gene. These findings provide valuable insights into the genetic mechanisms underlying color variation in P. yezoensis . Importantly, the genetically stable green mutant RG characterized here represents a promising germplasm resource for cross-breeding in Pyropia species. Furthermore, the improved crossing method applied in this study will facilitate genetic research and cross-breeding efforts in Pyropia aquaculture.