Transcriptional differences of genes involved in photosynthesis correlate with thallus morphological traits in two strains of Pyropia yezoensis

Pyropia yezoensis is a favourite food and economic crop in East Asia; however, in recent years, its production and economic benefits have been declining. The growth traits of germplasm are fundamental factors determining yield, often closely related to the length-to-width ratio of the blades. In this study, two strains of P. yezoensis with different morphotypes (long and wide blade shapes) were used, and transcriptomic sequencing and analysis were conducted on the top, central, and edge regions of each thallus. The results indicate that although the gene transcription levels are similar among different parts of the same blade shape, significant differences in the abundance of products from photosynthesis-related genes such as psbA and cpcB were observed at the top of the thallus between two blade shapes. Co-expression network analysis identified gene modules significantly positively correlated with the strain of long-blade shape, involving genes such as chlB related to chlorophyll synthesis in photosynthesis, the cytochrome f/b6 complex petA, and the phycocyanin apcE mainly located in chloroplasts or plastids. Therefore, differences in the traits of long and wide blade shapes of P. yezoensis may manifest in photosynthesis-related functions at the top of the thallus. Among the differentially expressed gene sequences of the two blade shapes of P. yezoensis, SSR sites dominated by tri-nucleotide repeats were identified, suggesting the potential for developing EST-SSR markers to distinguish between long and wide blade shapes. Elucidating the gene transcription characteristics associated with blade morphology in P. yezoensis is valuable for identifying and cultivating new high-yield strains of this seaweed.