ABA transport at the nexus of nutrient deficiency and water stress in plants

农业粮食生产严重依赖矿物肥料。迄今为止，全球每年仅磷肥的使用量就达到4300万吨。欧盟委员会已将P列为“关键原材料”，英国100%依赖进口。加上对环境和人类健康的负面影响，目前的磷使用率显然是不可持续的。因此，开发种植磷投入较少的作物的方法对国家和全球粮食安全至关重要。由于它们久坐不动的生活方式，植物是危险的，当它们感知到环境挑战时，它们会为最坏的情况做准备。它们具有检测磷供应减少并立即作出反应的机制。高亲和力运输和根分枝的上调增强了土壤“采矿”，而生长和能量消耗的下调则保护了内部资源。如果我们能推迟后者，优化前者，我们就有机会缩小表观产量和潜在产量之间的差距。然而，为了通过作物育种或基因组编辑将这些想法付诸实践，我们需要精确了解支持植物对缺磷的早期反应的分子信号传导途径。考虑到水资源短缺和气候变化，我们还需要知道这些途径是否与介导干旱或盐侵入引起的渗透胁迫反应的途径相互作用。我们最近发现，敲除拟南芥中一个名为NPF4.2的基因完全消除了低磷条件下的早期主根抑制。NPF4.2编码脱落酸（阿坝）转运蛋白。并且位于位于根的中央脉管系统中的细胞的液泡膜上。虽然npf4.2突变体的根在低P下继续生长，但它们仍然可以被其他营养缺乏或盐抑制。这些发现不仅突出了一个全新的角色的“应激激素”阿坝的缺磷反应，但也指出了新的作用阿坝转运赋予途径的特异性。该项目的目的是精确地映射的差异和收敛的信号通路，抑制根生长响应低磷和渗透胁迫和定位NPF4.2在这个网络中。为此，我们将利用A. thaliana.我们将采用最近开发的技术，在体内ABA成像和单细胞转录组学以及反向遗传学和蛋白质生物化学。拟议的工作方案有三个部分。工作包1将提供空间地图的压力诱发阿坝签名的根，这将与相关信号的响应模式，如Ca 2+，ROS和pH值，并与空间根转录组。工作包2将告诉我们NP4.2如何与其他ABA转运蛋白和动员ABA储存形式的酶合作，形成信号特征。该工作包还将确定NPF4.2和先前确定的低磷信号传导途径组分（如铁氧化酶和CLE肽）之间的关系。最后一个工作包将产生关于NPF4.2蛋白如何调节的信息。将从转录组学研究中选择候选靶标，特别强调与低磷诱导的CIPK和CBL基因家族成员的相互作用。已知CBL/CIPK调节子以Ca 2+依赖的方式激活膜转运蛋白，从而实现营养和盐胁迫的响应。然而，在调节阿坝运输的作用将是完全新颖的。预期的结果将提供一个基础科学基础，为'智能'作物的发展相结合，提高资源利用与鲁棒性对非生物胁迫。我们将确定信号通路中的关键点，使我们能够解耦或连接不同的信号输入和响应输出。因此，这项研究将为不同环境下的精准农业提供新的机会。

Agricultural food production heavily relies on mineral fertilization. To date, the global annual use of phosphorous (P) fertilizer alone stands at 43 Mio tons. The European Commission has classified P as a 'critical raw material' and the UK is 100% reliant on import. Adding the negative impacts on environment and human health, the current rate of P use is clearly not sustainable. Developing ways to grow crops with less P input is therefore paramount for national and global food security. Due to their sedentary lifestyle, plants are risk-adverse and prepare for the worst-case scenario when they perceive environmental challenges. They have mechanisms to detect a decrease in P supply and immediately react. Up-regulation of high-affinity transport and root branching enhances soil 'mining' while down-regulation of growth and energy consumption safeguards internal resources.. If we can delay the latter and optimize the former, we have an opportunity to close the gap between apparent and potential yield. However, to put these ideas into practice through crop breeding or genome editing, we need a precise understanding of molecular signalling pathways that underpin early responses of plants to P deficiency. Considering water shortage and climate change, we also need to know whether these pathways interact with those mediating responses to osmotic stress imposed by drought or salt intrusion.We recently discovered that knockout of a gene called NPF4.2 in Arabidopsis thaliana completely abolishes early main root inhibition in low P. NPF4.2 encodes a transporter for abscisic acid (ABA) and is located on the vacuolar membrane of cells located in the central vasculature of the root. While the roots of npf4.2 mutants continue to grow in low P they can still be inhibited by other nutrient deficiencies or by salt. These findings not only highlight an entirely new role of the 'stress hormone' ABA for P-deficiency responses but also point to new role of ABA transporters for endowing the pathway with specificity. The aim of this project is to precisely map differences and convergence of the signalling pathways that inhibit root growth in response to low-P and osmotic stress and to position NPF4.2 in this network. To this end we will take advantage of the advanced tools available for A. thaliana. We will employ recently developed technology for in-vivo ABA-imaging and single-cell transcriptomics alongside reverse genetics and protein biochemistry. The proposed work programme has three parts. Work package 1 will deliver spatial maps of stress-evoked ABA signatures in roots, which will be overlaid with response patterns of related signals such as Ca2+, ROS and pH, and with spatial root transcriptomes. Work package 2 will tell us how NP4.2 shapes the signal signatures, in collaboration with other ABA-transporters and with enzymes that mobilize ABA-storage forms. This work package will also identify the relationship between NPF4.2 and previously identified components of the low-P signalling pathway such as ferroxidases and CLE peptides. The last work package will produce information on how the NPF4.2 protein is regulated. Candidate targets will be selected from the transcriptomics studies with particular emphasis on interactions with low-P induced members CIPK and CBL gene families. CBL/CIPK regulons are already known for activating membrane transporters in a Ca2+-dependent manner thereby effectuating responses nutrient and salt stress. However, a role in regulating ABA transport would be entirely novel.The expected outcomes will provide a fundamental science base for the development of 'smart' crops combining improved resource use with robustness against abiotic stress. We will identify key points in the signalling pathways that will allow us to de-couple or connect different signal inputs and response outputs. This research will therefore open offers new opportunities for precision agriculture in different environment scenarios.