Arabidopsis thaliana TERMINAL FLOWER2 is involved in light-controlled signalling during seedling photomorphogenesis

Plants respond to changes in the environment by altering their growth pattern. Light is one of the most important environmental cues and affects plants throughout the life cycle. It is perceived by photoreceptors such as phytochromes that absorb light of red and far-red wavelengths and control, for example, seedling de-etiolation, chlorophyll biosynthesis and shade avoidance response. We report that the terminal flower2 (tfl2) mutant, carrying a mutation in the Arabidopsis thaliana HETEROCHROMATIN PROTEIN1 homolog, functions in negative regulation of phytochrome dependent light signalling. tfl2 shows defects in both hypocotyl elongation and shade avoidance response. Double mutant analysis indicates that mutants of the red/far-red light absorbing phytochrome family of plant photoreceptors, phyA and phyB, are epistatic to tfl2 in far-red and red light, respectively. An overlap between genes regulated by light and by auxin has earlier been reported and, in tfl2 plants light-dependent auxin-regulated genes are misexpressed. Further, we show that TFL2 binds to IAA5 and IAA19 suggesting that TFL2 might be involved in regulation of phytochrome-mediated light responses through auxin action. The participation of TERMINAL FLOWER2 (TFL2), the Arabidopsis thaliana HETEROCHROMATIN PROTEIN1 homolog, in light signalling has been proposed due to the early flowering and reduced sensitivity to day length displayed by tfl2 mutants. We report that TFL2 affects the phytochrome-dependent light signalling during seedling photomorphogenesis, and that light-dependent auxin-regulated genes are misexpressed in tfl2 plants. Moreover, TFL2 interacts with the IAA5 and IAA19 proteins, suggesting that TFL2 might be involved in regulation of phytochrome-mediated light responses through auxin action.