THE PLANT ONCOGENE ROLB STIMULATES THE FORMATION OF FLOWER AND ROOT MERISTEMOIDS IN TOBACCO THIN CELL-LAYERS

The expression and effects of the plant oncogene rolB during in vitro flower and root morphogenesis were investigated. Thin cell layers (TCL ) were excised from floral pedicels and from stems of transgenic tobac co plants containing either rolB and the promoter of rolB fused to the GUS reporter gene (BpB-GUS plants) or only this latter construct (pB- GUS plants). Organogenesis and GUS activity were monitored in pedicel and stem TCLs for 30 days under conditions of floral or root neoformat ion. Both flowering and rhizogenesis are substantially enhanced and mo re precocious in rolB-transformed explants than in TCLs from pB-GUS an d control plants. Most interestingly, both in flower and in root neofo rmation, meristemoids are much more numerous and appear sooner in rolB -transformed tissues. Thus, the effect of rolB does not seem to be spe cifically the induction of rooting, but, rather, the promotion of meri stem formation, regardless of subsequent differentiation. In addition, we provide evidence that the presence of the gene product of rolB doe s not alter the pattern and timing of expression of the gene.