Gene Expression Profiles of Amaranthin-Like Proteins with Distinct Domain Combinations in Flax (Linum usitatissimum)

Amaranthin-like proteins are lectins with distinct domain organization, but their functions in plants remain unclear. Flax (Linum usitatissimum) has one of the largest Amaranthin protein family among plant species, with 19 members grouped into three types of domain combinations: single amaranthin domain (A), two amaranthin domains with one aerolysin domain (AAT), and one or two amaranthin domains with one Bet v 1 domain (AB/AAB). In this study, we examined the expression of 13 amaranthin-like genes. Genes encoding proteins with a single amaranthin domain were active during early development and showed temporary upregulation in phloem fibers and xylem tissues after gravistimulation, suggesting possible roles in cell wall rearrangement and biosynthesis. AB2 and AAB2 genes were mainly expressed in phloem fibers at later stages, indicating possible involvement in phloem fiber formation. AAT1 was the only gene clearly expressed during intrusive phloem fiber growth. These results reveal that the different protein domain combinations correspond to distinct, tissue- and stage-specific gene expression patterns, pointing to specialized roles in phloem fiber formation, xylem development, and cell wall dynamics, and highlight candidate genes for further functional studies.