Examining the molecular basis of bast fibre development in flax (Linum usitatissimum L.)

Flax bast fibres are characterized by having an extremely long length and a thick, gelatinous secondary cell wall. To better understand the molecular processes associated with the development of bast fibre cells within the phloem of flax stems, a tissue-specific cDNA library and microarray were created. These tools were used to study gene expression in flax stems and hypocotyls during specific stages of fibre development: (1) elongation (2) onset of secondary wall deposition, (3) late secondary wall deposition. Transcripts enriched at the onset of secondary wall deposition in both flax stems and hypocotyls included a beta-galactosidase (LuBGAL1) and a fasciclin-like arabinogalactan protein (LuFLA1). Subsequent analysis of beta-galactosidase activity in hypocotyls confirmed its localization to post-elongation phloem fibres. Transgenic analysis of LuBGAL1 and LuFLA1 expression in flax was conducted to characterize the roles of these genes in bast fibre development. RNAi lines with reduced LuBGAL1 expression showed alterations in the thickness and composition of the flax fibre cell wall. On the other hand, RNAi lines with reduced LuFLA1 expression did not show any significant difference in fibre properties compared to wild-type. These results suggest an important regulatory role for LuBGAL1 in the development and modification of the flax bast fibre cell wall and validate the use of large-scale transcript profiling for the identification of novel candidate genes involved in flax bast fibre development.