Because chitin is the major component of fungal cell walls, chitinases are classic pathogenesis-related proteins involved in non-host-specific defense. Plants also contain chitinase-like proteins that are not induced by pathogens or stresses. In many cases, these chitinase-like proteins have been shown to lack detectable chitinase activity. Chitinase-like proteins may play an important role during normal plant growth and development. For example, AtCTL1 is constitutively expressed in many organs of Arabidopsis. Mutations of AtCTL1 lead to ectopic deposition of lignin in the secondary cell wall, reduction of root and hypocotyl lengths, and increased numbers of root hairs. It was suggested that this gene could be involved in root expansion, cellulose biosynthesis, and responses to several environmental stimuli. In particular, coexpression of some CTLs with secondary cell wall cellulose synthases was reported. It has been suggested that these chitinase-like proteins could take part in cellulose biosynthesis and play a key role in establishing interactions between cellulose microfibrils and hemicelluloses. The xylan-type secondary wall is the most common secondary wall in land plants and is characteristically rich in cellulose, xylan, and lignin. Compared to typical xylan-type secondary walls, gelatinous layers are enriched in cellulose, have a higher degree of cellulose crystallinity, larger crystallites, and a distinctive set of matrix polysaccharides. Presumably, cellulose synthase genes have a significant role in gelatinous cell wall formation, but the expression patterns of the complete flax CESA family has not been described to date. It is known that at least three PF 4778574 isoforms of CESAs comprise the cellulose synthase rosette: CESA1, CESA3, and CESA6 are required for cellulose biosynthesis in primary cell walls, whereas CESA4, CESA7, and CESA8 are required for cellulose biosynthesis during secondary wall deposition. Flax is a useful model for comparative studies of cell wall development: different parts of the flax stem form a primary cell wall, xylan type secondary cell wall, or gelatinous cell wall; these stem parts may be separated and analyzed by diverse approaches, including functional genomics. Furthermore, the iMAC2 publication of a flax whole genome assembly facilitates a thorough study of key gene families. In the present study, we measured expression of all predicted LusCTL genes of the GH19 family in various tissues including those that produce gelatinous-type and xylan-type cell walls.