LAUSR

Abstract Phytohormones are key regulators of plant growth and development. The plant hormone brassinosteroid (BR) is known to modulate many plant physiological processes via unknown molecular mechanisms. Here, BR and its biosynthetic inhibitor brassinazole (Brz) were studied in flax (Linum usitatissimum L.). Agronomic parameters were measured after spraying various concentrations of BR and Brz onto leaves during rapid growth and budding stages. Using Solexa/Illumina digital gene expression methodology to generate gene expression profiles, a total number of 3163 differentially expressed genes (DEGs) were identified in flax stem tissues treated with BR or Brz for 12 h during the budding stage. A stronger positive effect was exerted on plant agronomic parameters by Brz than BR, with 466, 2135, and 562 DEGs identified from pairwise comparisons of BR vs control check (CK), Brz vs CK, and Brz vs BR, respectively. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis assigned 817 DEGs to 237 biological pathways. DEGs related to cellulose and lignin biosynthesis, flax cell development, transcription factors, and phytohormones were up-regulated upon Brz treatment compared with CK. These results deepen the understanding of molecular mechanisms of plant hormone responses in flax, and provide new insights toward improving fiber yield and quality for flax.