LIPM, Université de Toulouse, INRA, CNRS, 31326, Castanet-Tolosan, France.
Sainsbury Laboratory, Cambridge University, 47 Bateman Street, Cambridge, CB2 1LR, UK.
New Phytol. 2019 Mar;221(4):2190-2202. doi: 10.1111/nph.15551. Epub 2018 Nov 24.
Lipo-chitooligosaccharides (LCOs) are microbial symbiotic signals that also influence root growth. In Medicago truncatula, LCOs stimulate lateral root formation (LRF) synergistically with auxin. However, the molecular mechanisms of this phenomenon and whether it is restricted to legume plants are not known. We have addressed the capacity of the model monocot Brachypodium distachyon (Brachypodium) to respond to LCOs and auxin for LRF. For this, we used a combination of root phenotyping assays, live-imaging and auxin quantification, and analysed the regulation of auxin homeostasis genes. We show that LCOs and a low dose of the auxin precursor indole-3-butyric acid (IBA) stimulated LRF in Brachypodium, while a combination of LCOs and IBA led to different regulations. Both LCO and IBA treatments locally increased endogenous indole-3-acetic acid (IAA) content, whereas the combination of LCO and IBA locally increased the endogenous concentration of a conjugated form of IAA (IAA-Ala). LCOs, IBA and the combination differentially controlled expression of auxin homeostasis genes. These results demonstrate that LCOs are active on Brachypodium roots and stimulate LRF probably through regulation of auxin homeostasis. The interaction between LCO and auxin treatments observed in Brachypodium on root architecture opens interesting avenues regarding their possible combined effects during the arbuscular mycorrhizal symbiosis.
脂寡糖（LCOs）是微生物共生信号，也影响根的生长。在紫花苜蓿中，LCOs 与生长素协同刺激侧根形成（LRF）。然而，这种现象的分子机制以及它是否仅限于豆科植物尚不清楚。我们研究了模式单子叶植物拟南芥（Brachypodium）对 LCOs 和生长素刺激 LRF 的反应能力。为此，我们使用了根表型分析、活体成像和生长素定量分析的组合，并分析了生长素稳态基因的调控。我们表明，LCOs 和低剂量的生长素前体吲哚-3-丁酸（IBA）刺激拟南芥的 LRF，而 LCOs 和 IBA 的组合则导致不同的调节。LCO 和 IBA 处理都局部增加了内源吲哚-3-乙酸（IAA）的含量，而 LCO 和 IBA 的组合则局部增加了 IAA 的一种共轭形式（IAA-Ala）的内源性浓度。LCOs、IBA 和它们的组合分别控制生长素稳态基因的表达。这些结果表明，LCOs 在拟南芥根上是活跃的，并通过调节生长素稳态来刺激 LRF。在根构型上观察到的 LCO 和生长素处理在拟南芥中的相互作用，为它们在丛枝菌根共生中的可能联合效应提供了有趣的途径。
