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22 Light Signal Transduction and the Control of Seedling Development

Joanne Chory, Ronald E. Susek


Numerous environmental factors, including temperature, touch, water, gravity, and light, influence plant development. For the emerging seedling whose development is governed by strategies that maximize photosynthetic capacity, light serves an especially important role. Light stimulates chloroplast biogenesis, leaf meristem differentiation, and induction of the coordinate expression of many light-regulated nuclear and chloroplast-encoded genes. This light-dependent development of plants, called photomorphogenesis, is controlled by the combined action of several photoreceptor systems within the plant. The biochemistry and molecular biology of the signal transduction and developmental pathways that lead to leaf and chloroplast biogenesis are largely unknown.

Although very little is known about the mechanisms of light signal transduction in plants, several approaches are beginning to yield new insight into the number and complexity of the pathways involved. This chapter highlights advances in three separate areas: (1) the biochemical analysis of the photoreceptors, (2) the identification of the cis-acting sequences and trans-acting factors that regulate the downstream light-regulated genes, and (3) the genetic dissection of the photoreceptor action pathways and signaling pathways that control chloroplast development. In particular, we focus on recent molecular, biochemical, and genetic studies that have aided in the dissection of the red and blue light signal transduction pathways that affect leaf and chloroplast development and the expression of nuclear light-regulated genes encoding chloroplast-destined proteins in dicots. We also discuss various mutations that affect nuclear control of chloroplast development and chloroplast signaling back to genes in the nuclear compartment. Although most of what has been learned about the biochemistry...

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