Identification and Expression Analysis of the Formin Gene Family in Neopyropia yezoensis Under Different Environmental Conditions

Background/Objectives: Neopyropia yezoensis is an economically important intertidal red alga that frequently experiences fluctuations in temperature, light intensity, and water availability. Formins are key regulators of actin nucleation and cytoskeletal dynamics, but their functions and stress-responsive roles in red algae remain poorly understood. This study aimed to systematically identify and characterize the Formin gene family in N. yezoensis and investigate their expression responses to different environmental stresses. Methods: Formin family members were identified from the N. yezoensis genome using HMMER and BLAST (2.17.0) searches based on the conserved FH2 domain, followed by domain validation. Gene structures, conserved motifs, physicochemical properties, predicted subcellular localization, protein structures, chromosomal distribution, phylogenetic relationships, and cis-acting elements in the upstream regions were analyzed. The expression patterns of the identified Formin genes were further examined by qRT-PCR under different temperature (4, 10, and 24 °C), light intensity (20, 60, and 100 μmol photons m−2 s−1), and desiccation/rehydration conditions. Results: Three Formin genes, designated NpyFormin01–03, were identified in N. yezoensis. All three encoded proteins contained the conserved FH2 domain but differed in motif composition, domain architecture, predicted subcellular localization, and structural features. NpyFormin01 contained additional PTEN_C2 and PTP_DSP_cys domains, whereas NpyFormin02 and NpyFormin03 contained only the FH2 domain. Phylogenetic analysis showed that the N. yezoensis Formins clustered with Formins from other red algae. Promoter analysis identified multiple predicted cis-acting elements associated with light, temperature, environmental, and phytohormone responses. Expression analysis revealed distinct responses among the three genes under the tested environmental conditions. Notably, NpyFormin01 was significantly upregulated under high-temperature treatment (24 °C), whereas NpyFormin02 and NpyFormin03 showed no statistically significant expression changes under the tested conditions. Conclusions: This study provides a systematic characterization of the Formin gene family in N. yezoensis. The differences in protein architecture, structural features, promoter cis-acting elements, and environmental-responsive expression patterns suggest potential functional divergence among NpyFormins. In particular, NpyFormin01 represents a potential heat-responsive candidate gene and may contribute to cytoskeletal regulation during environmental stress adaptation in N. yezoensis. These findings provide a basis for further investigation of the molecular functions of Formins in red algae.