Alterations of Endogenous Cytokinins in Transgenic Plants Using a Chimeric Isopentenyl Transferase Gene

Abstract

Cytokinins, a class of phytohormones, appear to play an important role in the processes of plant development. We genetically engineered the Agrobacterium tumefaciens isopentenyl transferase gene, placing it under control of a heat-inducible promoter (maize hsp70). The chimeric hsp70 isopentenyl transferase gene was transferred to tobacco and Arabidopsis plants. Heat induction of transgenic plants caused the isopentenyl transferase mRNA to accumulate and increased the level of zeatin 52-fold, zeatin riboside 23-fold, and zeatin riboside 5[prime]-monophosphate twofold. At the control temperature zeatin riboside and zeatin riboside 5[prime]-monophosphate in transgenic plants accumulated to levels 3 and 7 times, respectively, over levels in wild-type plants. This uninduced cytokinin increase affected various aspects of development. In tobacco, these effects included release of axillary buds, reduced stem and leaf area, and an underdeveloped root system. In Arabidopsis, reduction of root growth was also found. However, neither tobacco nor Arabidopsis transgenic plants showed any differences relative to wild-type plants in time of flowering. Unexpectedly, heat induction of cytokinins in transgenic plants produced no changes beyond those seen in the uninduced state. The lack of effect from heat-induced increases could be a result of the transient increases in cytokinin levels, direct or indirect induction of negating factor(s), or lack of a corresponding level of competent cellular factors. Overall, the effects of the increased levels of endogenous cytokinins in non-heat-shocked transgenic plants seemed to be confined to aspects of growth rather than differentiation. Since no alterations in the programmed differentiation pattern were found with increased cytokinin levels, this process may be controlled by components other than absolute cytokinin levels.

Effects of 6-Benzylaminopurine and Ethephon Applications on Flowering and Morphology in Summer-to-Autumn-Flowering Chrysanthemum under Open Field Conditions

“…14) Cytokinin promotes the growth of leaf and lateral buds. [15][16][17] It was easy to promote adventitious buds with plant callus using auxin with a high concentration of cytokinin. 18,19) Therefore, cytokinin is thought to control chrysanthemum leaf shape with other growth regulators and can be used to induce morphological change.…”

Control of Outgrowth and Dormancy in Axillary Buds

“…ipt (isopentenyl transferase from Agrobacterium tumefaciens), and transgenic plants with reduced levels of IAA, e.g. iaaL (indole-3-acetic acid Lys synthetase from Pseudomonas savastanoi), have been produced and reported to exhibit reduced apical dominance (Medford et al, 1989;Romano et al, 1991). On the other hand, transgenic plants with elevated levels of IAA, e.g.…”

Development of an expression system using the heat shock protein 70 promoter in the red macroalga, Porphyra tenera

“…The regulatory region of the HSP70 gene is an excellent candidate for development of a promoter in Porphyra. HSP70 promoters, which provide both constitutive and stress-inducible expression, are widely utilized to express heterologous and homologous genes in eukaryotic organisms (Medford et al 1989;Schroda et al 2000). In the green alga, Chlamydomonas, the HSP70 promoter allows efficient transgene expression due to its constitutive expression and suppression of transgene silencing by sequence elements in the promoter (Schroda et al 2002).…”