A. Guivarch et al., TISSUE-SPECIFIC EXPRESSION OF THE ROLA GENE MEDIATES MORPHOLOGICAL-CHANGES IN TRANSGENIC TOBACCO, Plant molecular biology, 30(1), 1996, pp. 125-134
The spatial and temporal activity of the entire and individual promote
r domains of the rolA gene of Agrobacterium rhizogenes was investigate
d and correlated with the distinctive features of the phenotypes of tr
ansgenic tobacco plants. The GUS assay was performed in the presence o
f an oxidative catalyst during the development of transgenic plants ex
pressing chimeric genes containing the beta-glucuronidase coding seque
nce under the control of the different promoter domains. In situ hybri
dization was also used an transgenic plants harbouring rolA under the
control of the entire or deleted promoter. This paper demonstrates for
the first time that the entire rolA promoter, composed of domains, A,
B and C, is silent in seeds, then activated at the onset of germinati
on in the cotyledons and in the elongation zone of the radicle and is
finally expressed throughout the vegetative and floral phases. Domains
B + C, which were sufficient to induce wrinkled leaves and short inte
rnodes, were active in all the stem tissues, but only in the companion
cells of the phloem strands of the leaves. Domain C, which specified
a dwarf phenotype with normal leaves, was weakly expressed in the stem
vascular bundles and in the leaf internal phloem. These results indic
ate that the vascular bundles are the primary targets for the generati
on of the short internode phenotype. Furthermore, the local expression
of rolA in the stem vascular bundles induced a size reduction of the
surrounding parenchyma cells, suggesting the existence of some diffusi
ble factor(s) associated with the expression of the rolA gene.