Phytochrome transgenics: functional, ecological and biotechnological applications.

The phytochromes have important functions in regulating plant growth and development in response to signals perceived from the natural light environment. In particular, the phytochrome-mediated shade avoidance syndrome has major significance for competition between plants growing in natural dense communities. In recent years, the availability of DNA sequences coding for members of the phytochrome family has enabled the construction of transgenic plants that express these sequences to high levels. Introduced PHY genes expressed in heterologous or homologous hosts yield apoproteins that combine with chromophores and are physiologically functional. Physiological analysis of transgenic plants expressing introduced PHYA and PHYB coding sequences has contributed to understanding the functions of phytochromes A and B. Ecological experiments with transgenic PHYA expressers have provided a novel test of the adaptive plasticity hypothesis, and point the way to a transgenic programme to improve crop plants.