The auxin-insensitive bodenlos mutation affects primary root formation andapical-basal patterning in the Arabidopsis embryo

In Arabidopsis embryogenesis, the primary root meristem originates from des cendants of both the apical and the basal daughter cell of the zygote. We h ave isolated a mutant of a new gene named BODENLOS (BDL) in which the prima ry root meristem is not formed whereas postembryonic roots develop and bdl seedlings give rise to fertile adult plants. Some bdl seedlings lacked not only the root but also the hypocotyl, thus resembling monopteros (inp) seed lings. In addition, bdl seedlings were insensitive to the auxin analogue 2, 4-D, as determined by comparison with auxin resistant1 (axr1) seedlings. bd l embryos deviated from normal development as early as the two-cell stage a t which the apical daughter cell of the zygote had divided horizontally ins tead of vertically. Subsequently, the uppermost derivative of the basal dau ghter cell, which is normally destined to become the hypophysis, divided ab normally and failed to generate the quiescent centre of the root meristem a nd the central root cap. We also analysed double mutants. bdl mp embryos cl osely resembled the two single mutants, bdl and mp, at early stages, while bdl mp seedlings essentially consisted of hypocotyl but did form primary le aves. bdl axr1 embryos approached the mp phenotype at later stages, and bdl axr1 seedlings resembled Inp seedlings. Our results suggest that BDL is in volved in auxin-mediated processes of apical-basal patterning in the Arabid opsis embryo.