Repressing epigenetic regulation enhances exogenous gene expression in the macroalga <i>Pyropia yezoensis</i> (Rhodophyta)

Pyropia yezoensis, an economically valuable macroalga, occupies a pivotal position in evolutionary history as a red alga, making it an ideal model organism for investigating the evolution of photosynthesis. However, efficient genetic manipulation in P. yezoensis, particularly the stable expression of exogenous genes, presents substantial challenges. Major obstacles, including gene silencing, co-suppression, and unstable transgenerational inheritance, hinder progress in this field. Emerging evidence suggests that epigenetic modifications, including histone acetylation and deacetylation, play crucial roles in regulating endogenous gene expression. Nevertheless, whether these processes influence the expression of exogenous genes in P. yezoensis remains largely unexplored. In this study, we demonstrate that the expression of an exogenous gene can be enhanced by silencing the gene encoding Sin3-associated protein 30 (PySAP30), a critical component of the histone deacetylase (HDAC) complex. To evaluate exogenous gene expression in P. yezoensis, we employed the GUS reporter gene driven by the strong endogenous polyubiquitin gene promoter (PypUbi1). We designed a dual-ribozyme system, comprising hammerhead and hepatitis delta virus ribozymes, to generate antisense fragments targeting PySAP30 exons. This strategy effectively suppressed PySAP30 expression, resulting in a marked increase in both GUS transcript abundance and enzymatic activity. In contrast, transformants without PySAP30 interference showed low GUS activity and pronounced chimerism. Our findings confirm the repressive effect of epigenetic modification on exogenous gene expression in P. yezoensis and highlight a potential strategy for improving exogenous gene expression in macroalgae.