Transcription factor. Involved in the control of tapetum development. Required for male fertility and pollen differentiation, especially during callose deposition. Homodimer. Mostly expressed in anthers, and, to a lower extent, in young inflorescences undergoing meiosis and siliques. First observed in floral meristem and early anther primordia. Later detected in archesporial cells. From stage 4 to early stage 5, weakly expressed in precursors of the middle layer, tapetum and meiocytes. Strongly expressed in the tapetum from late anther stage 5 to early stage 6, and at a lower level in meiocytes.