Auxinic herbicides, mechanisms of action, and weed resistance: A look into recent plant science advances

Auxin governs dynamic cellular processes involved at several stages of plant growth and development. In this review, we discuss the mechanisms employed by auxin in light of recent scientific advances, with a focus on synthetic auxins as herbicides and synthetic auxin resistance mechanisms. Two auxin receptors were reported. The plasma membrane receptor ABP1 (Auxin Binding Protein 1) alters the structure and arrangement of actin filaments and microtubules, leading to plant epinasty and reducing peroxisomes and mitochondria mobility in the cell environment. The second auxin receptor is the gene transcription pathway regulated by the SCFTir/AFB ubiquitination complex, which destroys transcription repressor proteins that interrupt Auxin Response Factor (ARF) activation. As a result mRNA related with Abscisic Acid (ABA) and ethylene are transcribed, producing high quantities of theses hormones. Their associated action leads to high production of Reactive Oxygen Species (ROS), leading to tissue and plant death. Recently, another ubiquitination pathway which is described as a new auxin signaling route is the F-box protein S-Phase Kinase-Associated Protein 2A (SKP2A). It is active in cell division regulation and there is evidence that auxin herbicides can deregulate the SKP2A pathway, which leads to severe defects in plant development. In this discussion, we propose that SFCSKP2A auxin binding site alteration could be a new auxinic herbicide resistance mechanism, a concept which may contribute to the current progress in plant biology in its quest to clarify the many questions that still surround auxin herbicide mechanisms of action and the mechanisms of weed resistance.生长素（Auxin）调控植物生长发育多个阶段所涉及的动态细胞过程。本综述结合最新科学进展，探讨生长素发挥作用的分子机制，重点聚焦作为除草剂的合成生长素及其抗性机制。目前已报道两类生长素受体：质膜受体生长素结合蛋白1（Auxin Binding Protein 1，ABP1）可改变肌动蛋白丝与微管的结构及排布，引发植物偏上性生长，并降低细胞微环境中过氧化物酶体与线粒体的移动性。第二类生长素受体是受SCFTir/AFB泛素化复合物调控的基因转录通路：该复合物可降解阻碍生长素响应因子（Auxin Response Factor，ARF）激活的转录阻遏蛋白，进而转录与脱落酸（Abscisic Acid，ABA）及乙烯相关的基因，大量合成这两类激素。二者协同作用会诱导活性氧（Reactive Oxygen Species，ROS）大量产生，最终导致组织与植株死亡。近期研究发现另一类泛素化通路作为新型生长素信号通路，其核心为F盒蛋白S期激酶相关蛋白2A（S-Phase Kinase-Associated Protein 2A，SKP2A）。该通路参与细胞分裂调控，且有证据表明生长素类除草剂可紊乱SKP2A通路，引发植物发育的严重缺陷。在此讨论中，我们提出SCFSKP2A生长素结合位点的改变可作为一种新型生长素类除草剂抗性机制，这一概念可为当前植物生物学领域旨在阐明生长素类除草剂作用机制及杂草抗性机制等诸多未解问题的研究提供助力。