EMS Mutants and Functional Genomics to Dissect Cell Wall Biology in Flax

Flax is grown for both seeds and fibers. The fibers have been used since antiquity for textiles (linen) and are characterized by secondary cell walls that are rich in cellulose and poor in lignin. Fiber quality is intimately related to fiber cell architecture and cell wall structure. To obtain information about the molecular mechanisms regulating cell wall biosynthesis in flax our group has recently produced and characterized a flax EMS population for functional genomics. Histochemical screening of this population allowed us to identify 93 independent M2 mutant families showing ectopic lignification in the secondary cell wall of stem bast fibers. We have named this core collection the flax lbf mutants for lignified bast fibers and believe that this population represents a novel biological resource for investigating how fiber plants regulate lignin biosynthesis. As a proof of concept we characterized the lbf1 mutant and showed that the lignin content increased by 350 % in outer stem tissues containing bast fibers but was unchanged in inner stem tissues containing xylem. Immunological and chemical analyses revealed that lbf1 mutants also showed changes to other cell wall polymers. Whole genome transcriptomics of the lbf1 mutant revealed significant modifications in the expression of a number of genes potentially related to the observed phenotyope. Continued characterization of flax lbf mutants should provide new insights into how plants control cell wall biosynthesis thereby opening the way for the identification of new targets for engineered improvements in both flax and other fiber crops.