Abstract
The appropriate leaf position is essential to optimize photosynthesis and plant growth. In this study, we show that the Arabidopsis leaf position is appropriately regulated by blue light-mediated growth response. When 1-week-old seedlings were transferred to under red light and grown for 5 days, new petioles appeared almost horizontally and their leaves dangled. However, if a very weak blue light was superimposed on red light, the new petioles emerged obliquely to upward and the leaf surface faced toward light. This leaf positioning required both phototropin1 and NON-PHOTOTROPIC HYPOCOTYL 3 and resulted in a dramatic enhancement of plant growth. In nph3 mutant, neither proper leaf positioning nor leaf flattening by blue light was found, and blue light-induced growth enhancement was drastically reduced. We conclude that NPH3-mediated phototropin1 signaling optimizes the light perception through inducing both appropriate leaf positioning and leaf flattening, and enhances plant growth.
