Light has a dramatic effect on the development of plants. How does light switch on the activity of genes? Nam-Hai Chua and colleagues at Rockefeller University in New York have been examining several light-triggered genes that are active in specific plant tissues. They find that the signals for light activation, and also those for tissue specificity, are recognized even after the genes are moved by genetic engineering techniques to another species of plant.
Even the botanists’ distinction between the subclasses of flowering plants poses no barrier. A gene from wheat, a monocotyledon, was property turned on by light and expressed in the appropriate tissues in tobacco, a dicotyledon, Chua reports. In work with scientists at the Monsanto Co. of St. Louis, Chua and colleagues have moved DNA containing a light-activated gene from pea plants into petunia cells. Originally the DNA transferred included 1,000 nucleotides adjacent to the beginning of the protein-encoding region.
In subsequent experiments, the flanking region was repeatedly trimmed, and the level of gene expression declined. But light continued to activate the gene until only 35 nucleotides remained adjacent to the coding sequence. Chua concludes that this short segment of DNA must be at least in part responsible for light activation of the gene.