THE ROLE OF THE MONOPTEROS GENE IN ORGANIZING THE BASAL BODY REGION OF THE ARABIDOPSIS EMBRYO

The monopteros (mp) gene contributes to apical-basal pattern formation in the Arabidopsis embryo. mp mutant seedlings lack basal body struct ures such as hypocotyl, radicle and root meristem, and this pattern de letion has been traced back to alterations in the octant-stage embryo. Cells of the embryo proper and the uppermost cell of the suspensor fa il to establish division patterns that would normally generate the bas al body structures. The resulting absence of a morphological axis seem s to be responsible for another phenotypic trait of mp seedlings, vari able positioning of cotyledons. This relationship is suggested by weak mp seedling phenotypes in which the presence of a short hypocotyl is correlated with normal arrangement of cotyledons. Root formation has b een induced in mp seedlings grown in tissue culture. This result suppo rts the notion that the mp gene is required for organising the basal b ody region, rather than for making the root, in the developing embryo.