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

The size and shape of plant organs are highly responsive to the local environmental conditions. The embryonic stem, or hypocotyl, of the plant is one such organ that displays impressive phenotypic plasticity, and its length is affected by both light and temperature. After sensing surrounding vegetation, hypocotyls of shade avoiding species elongate to outcompete neighbouring plants and secure access to sunlight. A similar elongation response occurs when the plants are grown in high ambient temperatures. Previous studies have shown that this response is mediated by a family of transcription factors called PHYTOCHROME-INTERACTING FACTORS (PIFs). However, it is poorly understood how environmental light and temperature interact to affect plants at the morphological and molecular levels. Here, we examine the genetic and molecular basis of the response to low R/FR under warm ambient temperatures. We found that low R/FR combined with warm temperature dominantly regulate by PIF7 and exhibit a synergistic effect on hypocotyl growth, greater than either stimulus alone. While the synergistic response was dependent on PIF7 and the plant hormone auxin, we demonstrate that additional, yet unknown key factor/s must be involved, likely working downstream of the phyB-PIF-auxin module. As shade responses are known to affect crop yield 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. In addition, we point out key factors in this response that can potentially be modulated to minimize the negative effect on yield. Overall design: Two biological replicates of wild-type seedlings grown in constant LED white light (~70µE) at 21°C in white light (WL) for three 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 one, three, six, or 24 hours and sequenced to analyze the genes regulated by each condition.

植物器官的大小与形态高度响应局部环境条件。植物的胚轴（hypocotyl）便是一类展现出显著表型可塑性的器官，其长度同时受光照与温度的共同调控。当感知到周边植被的存在时，避阴物种的胚轴会伸长，以此超越邻近植株并抢占充足的光照资源；当植株处于高温环境时，也会出现类似的伸长响应。既往研究表明，这类响应由光敏色素互作因子（PHYTOCHROME-INTERACTING FACTORS，PIFs）家族的转录因子所介导。然而，目前对于环境光照与温度如何在形态学与分子层面协同影响植物的机制仍不甚明晰。本研究聚焦于暖温环境下低红光/远红光比值（R/FR）响应的遗传与分子基础。研究发现，低R/FR与高温这两个信号主要通过光敏色素互作因子7（PIF7）发挥协同调控作用，且二者对胚轴生长的协同效应强于任一单一刺激。尽管该协同响应依赖于PIF7与植物激素生长素，但本研究证实还存在尚未被发现的关键调控因子，其很可能作用于phyB-PIF-生长素模块的下游。鉴于避阴响应会影响诸多物种的作物产量与果实品质，本研究结果将有助于更精准地预测高密度种植（此时植株间相互遮阴）条件下，植物对环境温度升高的响应模式。此外，本研究明确了该响应通路中的关键靶点，可通过对其进行调控以尽可能降低遮阴响应对作物产量带来的负面影响。总体实验设计：本实验设置两组生物学重复，将野生型幼苗置于恒定LED白光（~70μE）、21℃条件下培养3天，随后将幼苗分为四组，分别转移至以下四种处理环境：21℃补充远红光的白光环境（21FR；R/FR=0.6）、30℃白光环境（30WL）、30℃补充远红光的白光环境（30FR；R/FR=0.6），以及继续保留在21℃白光环境（21WL）作为对照。分别在处理1、3、6及24小时后采集整株幼苗样品，通过测序分析各处理条件下的调控基因。