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

植物器官的大小与形态对环境条件具有高度响应性。植物的胚胎茎即下胚轴（hypocotyl），可响应光照与温度信号展现出表型可塑性（phenotypic plasticity）。避荫植物的下胚轴会伸长，以此超越邻近植株并获取充足光照；类似的伸长反应同样会在高温环境中发生。已知光敏色素互作因子（PHYTOCHROME-INTERACTING FACTORS, PIFs）家族转录因子是上述响应过程的核心调控因子。然而，环境光照与温度如何协同调控植物发育的分子机制仍有待深入解析。

本研究发现，低R/FR光质与高温环境组合会触发协同性的下胚轴生长响应，该过程依赖PIF7与植物激素生长素（auxin）。研究证实，在phyB-PIF-生长素调控模块的下游，必然存在尚未被发现的未知调控因子。鉴于避荫反应会影响诸多物种的产量、病原菌易感性与果实品质，本研究结果将有助于优化高密度种植（此时植株间存在相互遮荫）条件下，植物对环境温度升高的响应预测模型。

实验整体设计：将植物在恒定LED白光（~70µE）、21℃的白光环境（21WL）中培养4天，随后将其分别转移至以下4种处理条件：21℃补加远红光的白光环境（21FR；R/FR=0.6）、30℃白光环境（30WL）、30℃补加远红光的白光环境（30FR；R/FR=0.6），或继续保留在21WL环境中。在处理2小时后采集整株幼苗样品，通过测序分析PIF7的结合位点。