Transcriptome Analysis of Genes Responsive to Nutrient Level Changes in the Marine Red Alga Pyropia yezoensis (Nori)

The cultivation of the red alga Pyropia (nori) is among the most significant aquaculture industries in East Asia. Nutrient deficiency-induced "discoloration" poses a serious threat to the industry, substantially impacting both harvest quality and production levels. In this study, we conducted transcriptome analysis (RNA-Seq) of P. yezoensis to gain deeper insights into the molecular mechanisms underlying physiological responses to nutrient limitation that lead to discoloration. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis estimated that under nutrient-rich conditions, pathways involved in photosynthesis (carbon fixation) and respiration (tricarboxylic acid [TCA] cycle and glycolysis) are more activated. In contrast, under nutrient-deficient conditions, upregulation of genes related to the uptake of external substances and stress response was observed. Additionally, seven genes (ant1-2, pup, drg2, ankrd, bckdha, lhcb, and an unknown gene) identified from the RNA-Seq results as potential discoloration markers were successfully validated through RT-qPCR analysis. The fundamental molecular insights into discoloration in P. yezoensis provided by this study will aid in developing future discoloration prediction methods and breeding discoloration-resistant Pyropia varieties.