Plant Adaptation to Dynamically Changing Environment: The Shade Avoidance Response

Work from several laboratories, including ours, identified key transcription factor genes that underpin shade avoidance in Arabidopsis and uncovered complex molecular interaction between low R/FR light and hormone signalling pathways. Among hormones, auxin seems to have a central role in several aspects of shade avoidance. Many lines of evidence connect this hormone to the rapid elongation response provoked by light quality changes. Furthermore, evidence exists that auxin plays a pivotal role in Arabidopsis leaf and root responses to low R/FR as well, suggesting that this hormone may act as a coordinator of plant growth responses to environmental light quality changes. In Arabidopsis, shade avoidance is regulated by a balance of positive (PIFs) and negative (HFR1/SICS1) regulators which ensure a fast reshaping of the plant body towards an environment optimal for growth while at the same time avoiding an exaggerated reaction to Low R/FR. Persistency of a low R/FR signal enhances the activity of phyA, in turn, of HY5, a master regulator of deetiolation, thus suggesting that one way in which plants adapt to a shade enviropnment is by modulating the HY5 pathway.