A <scp> C ₂ H ₂ </scp> zinc finger transcription factor links a <scp>GWAS</scp> locus to linear growth in <i>Gracilariopsis lemaneiformis</i> via <scp>MCM</scp> helicase activation

Summary The genetic basis of linear growth rate in the red alga Gracilariopsis lemaneiformis remains poorly characterized. This study functionally characterized the gene LXC001294 , a prior genome‐wide association studies (GWAS) candidate associated with growth variation, to elucidate its molecular role. We employed phylogenetic analysis, yeast assays, and subcellular localization to characterize LXC001294. Its genome‐wide binding sites were identified by ChIP‐seq, and transcriptomic profiles of fast‐ (YT13) and slow‐growing (QHD9) strains were compared via RNA‐seq. Direct regulation of key targets was validated using yeast one‐hybrid and dual‐luciferase assays. LXC001294 was confirmed as a nuclear‐localized C 2 H 2 zinc finger transcription factor. Integrated multi‐omics analysis revealed its direct targeting and upregulation of five minichromosome maintenance ( MCM ) genes, core components of the DNA replication machinery, in the fast‐growing strain. We demonstrate that LXC001294 promotes algal growth by activating the MCM complex, thereby enhancing DNA replication. This study provides a mechanistic link from a GWAS signal to a growth phenotype in a macroalga and establishes the transcriptional regulation of replication licensing as a key node controlling growth rate in nonmodel species.