Twilight length alters growth and flowering time in Arabidopsis via <i>LHY</i>/<i>CCA1</i>.

Abstract

Decades of research have uncovered how plants respond to two environmental variables that change across latitudes and over seasons: photoperiod and temperature. However, a third such variable, twilight length, has so far gone unstudied. Here, using controlled growth setups, we show that the duration of twilight affects growth and flowering time via the <i>LHY/CCA1</i> clock genes in the model plant Arabidopsis. Using a series of progressively truncated no-twilight photoperiods, we also found that plants are more sensitive to twilight length compared to equivalent changes in solely photoperiods. Transcriptome and proteome analyses showed that twilight length affects reactive oxygen species metabolism, photosynthesis, and carbon metabolism. Genetic analyses suggested a twilight sensing pathway from the photoreceptors <i>PHY E</i>, <i>PHY B</i>, <i>PHY D</i>, and <i>CRY2</i> through <i>LHY/CCA1</i> to flowering modulation through the <i>GI-FT</i> pathway. Overall, our findings call for more nuanced models of day-length perception in plants and posit that twilight is an important determinant of plant growth and development.