Evolutionary analysis of the FTR1 gene family in Physcomitrium patens (Hedw.) Mitt and its function under iron stress

Fe Transporter 1 (FTR1), a high-affinity iron permease, facilitates the uptake of ferric ion (Fe³⁺) into cells. This study investigated the FTR1 gene family in the early terrestrial plant Physcomitrium patens (Hedw.) Mitt., integrating genome-wide identification, sequence analysis, evolutionary inference, subcellular localization, and expression profiling under iron stress. Three members of the PpFTR1 gene family (PpFTR1-1, PpFTR1-2, and PpFTR1-3) were mapped to chromosomes 15, 21, and 22, respectively. All three genes encoded proteins that contained the conserved REXXE Fe-binding motif; however, the second REXXE motif in the PpFTR1-3 protein was mutated. Bioinformatics analysis and protein subcellular localization experiments indicated that all three transmembrane proteins localized to the cell membrane. The PpFTR1-1 and PpFTR1-2 genes were significantly upregulated in response to both iron deficiency and iron excess, whereas PpFTR1-3 remained unresponsive. Phylogenetic analysis revealed that the FTR1 family is predominantly distributed in green algae, charophytes, and early terrestrial plants (e.g., mosses and ferns), with homologous FTR1 sequences entirely absent in seed plants. Notably, FTR1 sequences from early terrestrial plants exhibited closer evolutionary affinity to fungal homologs than to those of charophytes, the ancestral lineage of terrestrial plants, indicating a possible horizontal gene transfer event during terrestrialization. These findings not only provide a theoretical framework for understanding the molecular mechanisms by which early land plants adapted to iron stress but also offer insights into gene regulation mechanisms and the enhancement of iron uptake in crops.