Jiangsu Key Laboratory for Microbes and Functional Genomics, Jiangsu Engineering and Technology Research Center for Industrialization of Microbial Resources, College of Life Sciences, Nanjing Normal University, Jiangsu Province, China.
Department of Genetics and Plant Breeding, Sher-e-Bangla Agricultural University, Dhaka, Bangladesh.
Plant Cell Physiol. 2018 Sep 1;59(9):1889-1904. doi: 10.1093/pcp/pcy107.
Allelopathy is mediated by plant-derived secondary metabolites (allelochemicals) which are released by donor plants and affect the growth and development of receptor plants. The plant root is the first organ which senses soil allelochemicals this results in the production of a shorter primary root. However, the mechanisms underlying this process remain elusive. Here, we report that a model allelochemical benzoic acid (BA) inhibited primary root elongation of Arabidopsis seedlings by reducing the sizes of both the meristem and elongation zones, and that auxin signaling affected this process. An increase in auxin level in the root tips was associated with increased expression of auxin biosynthesis genes and auxin polar transporter AUX1 and PIN2 genes under BA stress. Mutant analyses demonstrated that AUX1 and PIN2 rather than PIN1 were required for the inhibition of primary root elongation during BA exposure. Furthermore, BA stimulated ethylene evolution, whereas blocking BA-induced ethylene signaling with an ethylene biosynthesis inhibitor (Co2+), an ethylene perception antagonist (1-methylcyclopropene) or ethylene signaling mutant lines etr1-3 and ein3eil1 compromised BA-mediated inhibition of root elongation and up-regulation of auxin biosynthesis-related genes together with AUX1 and PIN2, indicating that ethylene signal was involved in auxin-mediated inhibition of primary root elongation during BA stress. Further analysis revealed that the BA-induced reactive oxygen species (ROS) burst contributed to BA-mediated root growth inhibition without affecting auxin and ethylene signals. Taken together, our results reveal that the allelochemical BA inhibits root elongation by increasing auxin accumulation via stimulation of auxin biosynthesis and AUX1/PIN2-mediated auxin transport via stimulation of ethylene production and an auxin/ethylene-independent ROS burst.
化感作用是由植物来源的次生代谢物（化感物质）介导的，这些物质由供体植物释放，并影响受体植物的生长和发育。植物的根是第一个感知土壤化感物质的器官，这导致初生根变短。然而，这个过程的机制仍然难以捉摸。在这里，我们报告说，一种模式化感物质苯甲酸（BA）通过减少分生组织和伸长区的大小来抑制拟南芥幼苗的初生根伸长，而生长素信号转导影响了这个过程。BA 胁迫下，根尖生长素水平的增加与生长素生物合成基因和生长素极性转运体 AUX1 和 PIN2 基因的表达增加有关。突变体分析表明，AUX1 和 PIN2 而不是 PIN1 在 BA 暴露期间抑制初生根伸长是必需的。此外，BA 刺激乙烯的释放，而用乙烯生物合成抑制剂（Co2+）、乙烯感受拮抗剂（1-甲基环丙烯）或乙烯信号突变体线 etr1-3 和 ein3eil1 阻断 BA 诱导的乙烯信号，会损害 BA 介导的根伸长抑制和生长素生物合成相关基因的上调以及 AUX1 和 PIN2，表明乙烯信号参与了 BA 胁迫下生长素介导的初生根伸长抑制。进一步分析表明，BA 诱导的活性氧（ROS）爆发有助于 BA 介导的根生长抑制，而不影响生长素和乙烯信号。总之，我们的结果表明，化感物质 BA 通过刺激生长素生物合成和 AUX1/PIN2 介导的生长素运输来增加生长素积累，从而抑制根伸长，这是通过刺激乙烯产生和生长素/乙烯非依赖的 ROS 爆发实现的。
