The rolD gene from Agrobacterium rhizogenes is developmentally regulated in transgenic tobacco

The rolD gene from Agrobacterium rhizogenes has recently been shown to induce striking precocity of flowering in transgenic tobacco. A transcriptional fusion between 578 bp of the rolD upstream regulating sequence and the GUS reporter gene has been transferred to tobacco plants and its expression analysed throughout the whole life cycle of the plant. A detailed histological analysis revealed that rolD is strongly expressed in elongating and differentiating tissues of each organ, from the mature embryo to the adult plant. In organs with determinate growth, such as cotyledons, leaves and floral parts, rolD expression follows the age gradient of the tissues. In mature tissues, rolD expression is high, begins to decrease with ageing and is switched off when senescence occurs. RolD is also active in the vascular system, in the procambium, pith- and receptacular-meristems. Our data show that expression of rolD is under developmental control as it correlates with, and may represent a molecular marker for, the elongation/expansion and maturation phases of the plant tissues.