Transcription factor that regulates secondary cell wall (SCW) biosynthesis, especially in interfascicular and xylary fibers. In elongating stem internodes, expressed in developing protoxylem and elongating interfascicular fiber cells. In non-elongating internodes, expressed in developing metaxylem cells and interfascicular fibers. In roots, expressed in developing secondary xylem. Plants silencing MYB54 exhibit secondary cell wall (SCW) defects including severe reduction in SCW thickening in both interfascicular fibers and xylary fibers of inflorescence stems.