Light signal transduction: an infinite spectrum of possibilities

Abstract

The past 30 years has seen a tremendous increase in our understanding of the light-signaling networks of higher plants. This short review emphasizes the role that Arabidopsis genetics has played in deciphering this complex network. Importantly, it outlines how genetic studies led to the identification of photoreceptors and signaling components that are not only relevant in plants, but play key roles in mammals.

Figure 1

A 30-year timeline of light-signaling research. (a) Major discoveries in light signaling since 1980 that were made independently of the Arabidopsis system. (b) Discoveries made during the same period using Arabidopsis. Note that, during the past decade, it is hard to distinguish Arabidopsis-dependent contributions from independent ones.

Figure 2

Model for phytochrome signaling circa 1989.

Figure 3

Genetic model for light signaling circa 2000. Mutation in early signaling intermediates are expected to have a phenotype only under the specific light conditions activating their photoreceptor, and known molecules fitting this requirement include several transcription factors that directly interact with photoreceptors, as well as other molecules that are phosphorylated by phytochromes. The subcellular localization of phytochrome itself is light-regulated. Thus, in light signaling, there are direct interactions of photoreceptors, as well as cross-talk and integration of pathways both early and late in the signaling network.