Borghi Lorenzo, Kang Joohyun, de Brito Francisco Rita
Department of Plant and Microbial Biology, University of Zurich, Zurich, Switzerland.
Front Plant Sci. 2019 Apr 17;10:422. doi: 10.3389/fpls.2019.00422. eCollection 2019.
Plant hormones regulate a myriad of plant processes, from seed germination to reproduction, from complex organ development to microelement uptake. Much has been discovered on the factors regulating the activity of phytohormones, yet there are gaps in knowledge about their metabolism, signaling as well as transport. In this review we analyze the potential of the characterized phytohormonal transporters belonging to the ATP-Binding Cassette family (ABC proteins), thus to identify new candidate orthologs in model plants and species important for human health and food production. Previous attempts with phylogenetic analyses on transporters belonging to the ABC family suggested that sequence homology is not a powerful tool for functional characterization. However, we show here that sequence homology might indeed support functional conservation of characterized members of different classes of ABC proteins in several plant species, e.g., in the case of ABC class G transporters of strigolactones and ABC class B transporters of auxinic compounds. Also for the low-affinity, vacuolar abscisic acid (ABA) transporters belonging to the ABCC class we show that localization-, rather than functional-clustering occurs, possibly because of sequence conservation for targeting the tonoplast. The ABC proteins involved in pathogen defense are phylogenetically neighboring despite the different substrate identities, suggesting that sequence conservation might play a role in their activation/induction after pathogen attack. Last but not least, in case of the multiple lipid transporters belong to different ABC classes, we focused on ABC class D proteins, reported to transport/affect the synthesis of hormonal precursors. Based on these results, we propose that phylogenetic approaches followed by transport bioassays and investigations might accelerate the discovery of new hormonal transport routes and allow the designing of transgenic and genome editing approaches, aimed to improve our knowledge on plant development, plant-microbe symbioses, plant nutrient uptake and plant stress resistance.
植物激素调节着无数的植物生理过程，从种子萌发到繁殖，从复杂器官发育到微量元素吸收。关于调节植物激素活性的因素，人们已经有了很多发现，但在它们的代谢、信号传导以及运输方面，仍存在知识空白。在本综述中，我们分析了属于ATP结合盒家族（ABC蛋白）的已鉴定植物激素转运蛋白的潜力，从而在模式植物以及对人类健康和粮食生产至关重要的物种中鉴定新的候选直系同源物。先前对ABC家族转运蛋白进行系统发育分析的尝试表明，序列同源性并非功能表征的有力工具。然而，我们在此表明，序列同源性确实可能支持不同类别的ABC蛋白在几种植物物种中的已鉴定成员的功能保守性，例如，在独脚金内酯的ABC G类转运蛋白和生长素类化合物的ABC B类转运蛋白的情况下。同样，对于属于ABCC类的低亲和力液泡脱落酸（ABA）转运蛋白，我们表明发生的是定位聚类而非功能聚类，这可能是由于靶向液泡膜的序列保守性。尽管底物不同，但参与病原体防御的ABC蛋白在系统发育上相邻，这表明序列保守性可能在病原体攻击后它们的激活/诱导中起作用。最后但同样重要的是，对于属于不同ABC类别的多种脂质转运蛋白，我们重点关注了据报道可运输/影响激素前体合成的ABC D类蛋白。基于这些结果，我们提出，随后进行运输生物测定和研究的系统发育方法可能会加速新激素运输途径的发现，并允许设计转基因和基因组编辑方法，旨在增进我们对植物发育、植物 - 微生物共生、植物养分吸收和植物抗逆性的了解。
