Isopentenyl transferasegene (ipt) downstream transcriptionally fused with gene expression improves the growth of transgenic plants
This research reports a promising approach to increase a plant's physiological cytokinin content. This approach also enables the increase to play a role in plant growth and development by introducing the ipt gene to downstream transcriptionally fuse with other genes under the control of a CaMV35S promoter, in which the ipt gene is far from the 35S promoter. According to Kozak's ribosome screening model, expression of the ipt gene is reduced by the terminal codon of the first gene and the internal untranslated nucleotides between the fused genes. In the transgenic plants pVKH35S-GUS-ipt, pVKH35S-AOC-ipt, and pVKH35S-AtGolS2-ipt, cytokinins were increased only two to threefold, and the plants grew more vigorously than the pVKH35S-AOC or pVKH35S-AtGolS2 transgenic plants lacking the ipt gene. The vigorous growth was reflected in rapid plant growth, a longer flowering period, a greater number of flowers, more seed product, and increased chlorophyll synthesis. The AOC and AtGolS2 genes play a role in a plant's tolerance of salt or cold, respectively. When the ipt gene transcriptionally fuses with AOC or AtGolS2 in the frame of AOC-ipt and AtGolS2-ipt, slight cytokinin increases were obtained in their transgenic plants; furthermore, those increases played a positive role in improvements of plant growth. Notably, an increased cytokinin volume at the physiological level, in concert with AtGolS2 expression, enhances a plant's tolerance to cold.