The signal transducing photoreceptors of plants.

Light signals are amongst the most important environmental cues regulating plant development. In addition to light quantity, plants measure the quality, direction and periodicity of incident light and use the information to optimise growth and development to the prevailing environmental conditions. Red and far-red wavelengths are perceived by the photoreversible phytochrome family of photoreceptors, whilst the detection of blue and ultraviolet (UV)-A wavelengths is conferred by the cryptochromes and phototropins. Higher plants contain multiple discrete phytochromes, the apoproteins of which are encoded by a small divergent gene family. In Arabidopsis, two cryptochrome and two phototropin family members have been identified and characterized. Photoreceptor action regulates development throughout the lifecycle of plants, from seed germination through to architecture of the mature plant and the onset of reproduction. The roles of individual photoreceptors in mediating plant development have, however, often been confounded by redundant, synergistic and in some cases mutually antagonistic mechanisms of action. The isolation of mutants null for individual photoreceptors and the construction of mutants null for multiple photoreceptors have therefore been paramount in elucidating photoreceptor functions. Photoreceptor action does not, however, operate in isolation from other signalling systems. The integration of light signals with other environmental cues enables plants to adapt their physiology to changing seasonal environments. This paper summarises current understanding of photoreceptor families and their functions throughout the lifecycle of plants. The integration of light signals with other environmental stimuli is also discussed.