Donoso Raúl, Leiva-Novoa Pablo, Zúñiga Ana, Timmermann Tania, Recabarren-Gajardo Gonzalo, González Bernardo
Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Santiago, Chile.
Millennium Nucleus Center for Plant Systems and Synthetic Biology, Santiago, Chile.
Appl Environ Microbiol. 2016 Dec 15;83(1). doi: 10.1128/AEM.01991-16. Print 2017 Jan 1.
Several bacteria use the plant hormone indole-3-acetic acid (IAA) as a sole carbon and energy source. A cluster of genes (named iac) encoding IAA degradation has been reported in Pseudomonas putida 1290, but the functions of these genes are not completely understood. The plant-growth-promoting rhizobacterium Paraburkholderia phytofirmans PsJN harbors iac gene homologues in its genome, but with a different gene organization and context than those of P. putida 1290. The iac gene functions enable P. phytofirmans to use IAA as a sole carbon and energy source. Employing a heterologous expression system approach, P. phytofirmans iac genes with previously undescribed functions were associated with specific biochemical steps. In addition, two uncharacterized genes, previously unreported in P. putida and found to be related to major facilitator and tautomerase superfamilies, are involved in removal of an IAA metabolite called dioxindole-3-acetate. Similar to the case in strain 1290, IAA degradation proceeds through catechol as intermediate, which is subsequently degraded by ortho-ring cleavage. A putative two-component regulatory system and a LysR-type regulator, which apparently respond to IAA and dioxindole-3-acetate, respectively, are involved in iac gene regulation in P. phytofirmans These results provide new insights about unknown gene functions and complex regulatory mechanisms in IAA bacterial catabolism.
This study describes indole-3-acetic acid (auxin phytohormone) degradation in the well-known betaproteobacterium P. phytofirmans PsJN and comprises a complete description of genes, some of them with previously unreported functions, and the general basis of their gene regulation. This work contributes to the understanding of how beneficial bacteria interact with plants, helping them to grow and/or to resist environmental stresses, through a complex set of molecular signals, in this case through degradation of a highly relevant plant hormone.
几种细菌将植物激素吲哚 - 3 - 乙酸（IAA）用作唯一的碳源和能源。在恶臭假单胞菌1290中已报道了一组编码IAA降解的基因（命名为iac），但这些基因的功能尚未完全了解。植物促生根际细菌植物伯克霍尔德氏菌PsJN在其基因组中含有iac基因同源物，但其基因组织和背景与恶臭假单胞菌1290不同。iac基因功能使植物伯克霍尔德氏菌能够将IAA用作唯一的碳源和能源。采用异源表达系统方法，具有先前未描述功能的植物伯克霍尔德氏菌iac基因与特定的生化步骤相关。此外，两个未表征的基因，以前在恶臭假单胞菌中未报道，发现与主要促进剂和互变异构酶超家族有关，参与去除一种称为二氧吲哚 - 3 - 乙酸的IAA代谢物。与菌株1290的情况类似，IAA降解通过儿茶酚作为中间体进行，随后通过邻位环裂解降解。一个推定的双组分调节系统和一个LysR型调节因子，分别明显对IAA和二氧吲哚 - 3 - 乙酸作出反应，参与植物伯克霍尔德氏菌中iac基因的调节。这些结果为IAA细菌分解代谢中未知基因功能和复杂调节机制提供了新的见解。
本研究描述了著名的β-变形杆菌植物伯克霍尔德氏菌PsJN中吲哚 - 3 - 乙酸（生长素植物激素）的降解，并包括对基因的完整描述，其中一些基因具有以前未报道的功能，以及它们基因调控的一般基础。这项工作有助于理解有益细菌如何通过一组复杂的分子信号与植物相互作用，帮助它们生长和/或抵抗环境压力，在这种情况下是通过降解一种高度相关的植物激素。
