Molecular Characterization of the Linusitin‐like Gene Family from Flax

Osmotin-like proteins from the fifth class of pathogenesis-related proteins (PR-5), including linusitin that we isolated from flax seeds, have been characterized in many plant species. A cDNA library has been constructed from flax (Linum usitatissimum L.) seedlings to analyze the osmotin-like gene family from flax. A cDNA LIN1 was isolated from the library and found to exhibit significant similarities to genes encoding osmotin-like proteins and thaumatin from Thaumatococcus daniellii. The deduced LIN1 protein contains all 16 cysteine residues that are conserved in all PR-5 proteins as well as other residues important for antifungal activity. The LIN1 cDNA encodes a preprotein, which is subsequently processed into the mature protein by removal of an N-terminal signal peptide. Southern blot analysis showed that the LIN1 gene family is encoded by few copies in the flax genome. The gene encoding LIN1 is intronless and developmentally regulated, and transcripts accumulate in an organ-specific manner in healthy flax seedlings. The LIN1 mRNA was constitutively expressed, predominantly in root tissue. The comparison of N-terminus sequences from linusitin-like protein (LIN1) and previously isolated linusitin confirmed differences in amino acid composition and demonstrated the occurrence of at least two osmotin-like proteins in flax.