Photoreceptor Biotechnology

Plant photoreceptors influence or control almost all aspects of plant metabolism, growth and development. Only the extent and timing of this control is variable (see other chapters in this volume). Many agriculturally relevant traits are either heavily influenced or completely controlled by photoreceptors. These include seed germination, circadian timing, seedling architecture, bud dormancy, leaf shape and size, stem length and curvature, photosynthetic resource allocation, chloroplast development, chloroplast positioning, flowering time, grain filling and dormancy. In terms of metabolism, the enzymes and other protein components that mediate most of the reactions of photosynthesis are light regulated. Processes such as nitrogen fixation and gas exchange are also regulated by light and influenced by the circadian clock (which is itself is under direct photoreceptor control -see Devlin, this volume). The expression of many other genes and processes are controlled by, or interact with, photoreceptor pathways (see Josse and Halliday, this volume). One agronomically relevant example of this is that defense pathways are strongly influenced by photoreceptor signals (Genoud et al., 2002). Since many photoreceptor-controlled processes are important in determining the yield and suitability of crops, there has been significant interest for many years in using or modifying photoperception for crop improvement.