Light signal transduction in plants.

Abstract

Plants, as sessile organisms, have developed intricate signal transduction networks used to adapt to the changing environment surrounding them. One of the most important dynamic environmental factors is light, and the light control of dicotyledonous seedling development is one of the best studied examples. Before the developing seedling emerges from the soil it has the classic skotomorphogenic or etiolated morphology, containing a long hypocotyl with closed cotyledons and an apical hook. Plastids remain as etioplasts that lack developed membrane structures and have no photosynthetic capacity. Emergence of the seedling into the light triggers a profound developmental switch to photomorphogenesis, which results in short hypocotyls, open and expanded cotyledons and the lack of an apical hook. Chloroplasts develop and photosynthetic gene expression is derepressed. This changing morphological pattern is the result of vastly different modes of gene expression in the dark and the light. The sunlight that reaches the earth's surface ranges from UV to visible to infrared. Although the visible light (400700 nm) is most effective in driving photosynthesis, higher plants have adapted a sophisticated sensory system that is also able to sense the UV and far-red light. Moreover, higher plants not only sense the quality of the light surrounding them but also the direction and quantity of light. Extensive research in the past decades, particularly the last few years, has significantly improved our understanding of the photosensory system and the downstream signaling processes. Many components involved in this regulatory network have been identified and some of them have been characterized molecularly. This review attempts to provide a brief summary of recent progress, with particular emphasis on the effect of light on Arubidopsis seedling development. There are several excellent reviews on this and related subjects in the last 2 years (1-6) that are recommended for further information.