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Promoter tagging with a promoterless ipt gene leads to cytokinin‐induced phenotypic variability in transgenic tobacco plants: implications of gene dosage effects
Author(s) -
Hewelt Andreas,
Prinsen Els,
Schell Jeff,
Onckelen Harry,
Schmülling Thomas
Publication year - 1994
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1046/j.1365-313x.1994.6060879.x
Subject(s) - cytokinin , biology , meristem , apical dominance , transgene , gene , nicotiana tabacum , promoter , reporter gene , genetically modified crops , phenotype , genetics , microbiology and biotechnology , gene expression , botany , shoot , auxin
Summary Tobacco plants have been transformed with a T‐DNA construct harboring a promoterless cytokinin‐synthesizing ipt gene close to the right T‐DNA border. Eighteen out of 85 transgenic clones displayed phenotypic alterations typical for an enhanced cytokinin production. Northern blot analysis confirmed the transcriptional activation of the introduced gene by tagged plant promoters. The concentration of cytokinins, expressed as zeatinriboside equivalents, was increased up to sevenfold in transgenic tissues. These increases in cytokinin levels resulted in major developmental changes. Transgenic clones exhibited to different levels traits of a general cytokinin‐syndrome, i.e. reduced root growth, reduced apical dominance, reduced leaf surface, reduced growth of the stem and retarded leaf senescence or displayed localized and developmentally specific cytokinin‐induced alterations in otherwise normally developing plants. These traits were in particular a simultaneous break of dormancy in all axillary buds before or at the onset of flowering or the reorientation of the developmental pathway of secondary meristems or terminally differentiated cells. This indicates that endogenously produced cytokinins not only influence different growth parameters but have the potential to alter differentiation pattern. The results show that stably inherited developmental alterations due to a general or localized cytokinin overproduction can be obtained by the promoter‐tagging approach. The investigation of gene dosage effects in homozygote plants readresses the question of threshold levels for cytokinin effects on the developmental program of plants.