Dynamics of shade avoidance response in Arabidopsis

The success of competitive interactions between plants determines the chance of survival of individuals and eventually of whole plant species. Shade-tolerant plants have adapted their photosynthesis to function optimally under low light conditions. These plants are therefore capable of long-term survival under a canopy shade. In contrast, shade-avoiding plants adapt their growth to perceive maximum sunlight and therefore rapidly dominate gaps in a canopy. Daylight contains roughly equal proportions of red (R) and far-red (FR) light, but within vegetation that ratio is lowered as a result of R absorption by photosynthetic pigments. This light quality change is perceived through the phytochrome system as an unambiguous signal of the proximity of neighbours resulting in the shade avoidance response. This adaptive reaction is achieved by a set of responses including enhanced internode and petiole extension growth, increased apical dominance, retarded leaf development, and an acceleration of flowering. Genomic and genetic analyses by a number of laboratories including ours have identified several low R/FR regulated genes and key regulators involved in the shade avoidance response. However, very little is known about the cascade of events triggered by low R/FR that give rise to full activation of the response and eventually lead to adaptation to an unfavourable light environment. By combining genome-wide experimental and computational analyses in wild type and genetically altered plants exposed to low R/FR light for different times, we identified novel regulatory circuits controlling plant adaptation to canopy shade.