PICKLE chromatin-remodeling factor controls thermosensory hypocotyl growth of Arabidopsis.

Temperature is a major signal that governs plant distribution and shapes plant growth. High ambient temperature promotes plant thermomorphogenesis without significant induction of heat-stress responses. Although much progress of warm temperature-mediated plant growth has been made during recent years, the thermomorphogenic signalling pathway is not well understood. We previously revealed that PICKLE (PKL), an ATP-dependent chromatin remodelling factor, negatively controls photomorphogenesis in Arabidopsis thaliana. Here, we show that mutations in PKL lead to reduced sensitivity in hypocotyl elongation to warm temperature (28 °C). We demonstrate that CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1) directly binds to the specific promoter regions of PKL and its expression is reduced in the cca1 mutants. We find that the cca1 seedlings are also less sensitive to temperature-mediated growth than the wild-type plants. Furthermore, PKL affects the level of trimethylation of histone H3 Lys 27 associated with INDOLE-3-ACETIC ACID INDUCIBLE 19 (IAA19) and IAA29 and regulates their expression. We also identify 6 additional transcription factors as the upstream regulators of PKL. Our study thus reveals PKL and CCA1 as 2 novel factors in controlling plant growth in response to the elevated temperature environment and provides new insight into the integration of light and temperature signals through chromatin regulation.