PIF7 is the master regulator of thermomorphogenesis in shade [ChIP-seq]

The size and shape of plant organs are highly responsive to environmental conditions. The plant's embryonic stem, or hypocotyl, displays phenotypic plasticity, in response to light and temperature. The, hypocotyl of shade avoiding species elongate to outcompete neighbouring plants and secure access to sunlight. Similar elongation occurs in high temperature. PHYTOCHROME-INTERACTING FACTORS (PIFs) family transcription are known to be importenet players in these responses. However, it is poorly understood how environmental light and temperature interact to affect plants development. We found that low R/FR combined with warm temperature produces a synergistic hypocotyl growth response that dependent on PIF7 and the hormone auxin. We demonstrate that additional, unknown factor/s must be working downstream of the phyB-PIF-auxin module. As shade responses are known to affect yield, susceptibility to pathogens, and fruit quality in many species, our findings will improve the predictions of how plants will respond to increased ambient temperatures when grown at high density, a condition in which mutual shading occurs. Overall design: Plants were grown in constant LED white light (~70µE) at 21°C in white light (21WL) for four days and moved to 21°C WL supplement with Far-red (21FR; R/FR=0.6), 30°C in white light (30WL), 30°C WL supplement with Far-red (30FR; R/FR=0.6) or left at 21WL. Samples (whole seedlings) were collected after 2 hours and sequenced to analyze PIF7 binding.