Rhizobium Lipo-chitooligosaccharide Signaling Triggers Accumulation of Cytokinins in Medicago truncatula Roots  

作　　者：Arjan van Zeijl Rik H.M. Op den Camp Eva E. Deinum Tatsiana Charnikhova Henk Franssen Huub J.M. Op den Camp Harro Bouwmeester Wouter Kohlen Ton Bisseling Rene Geurts 

机构地区：[1]Department of Plant Sciences, Laboratory of Molecular Biology, Wageningen University, Droevendaalsesteeg 1,6708 PB Wageningen, The Netherlands [2]Department of Systems Biophysics, FOM institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands [3]Department of Plant Sciences, Laboratory of Plant Physiology, Wageningen University, Droevendaalsesteeg 1, 6708 PB Wageningen, The Netherlands [4]Department of Microbiology, IWWR, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands [5]College of Science, King Saud University, Post Office Box 2455, Riyadh 11451, Saudi Arabia

出　　处：《Molecular Plant》2015年第8期1213-1226,共14页分子植物（英文版）

摘　　要：Legume rhizobium symbiosis is initiated upon perception of bacterial secreted lipo-chitooligosaccharides （LCOs）. Perception of these signals by the plant initiates a signaling cascade that leads to nodule formation. Several studies have implicated a function for cytokinin in this process. However, whether cytokinin accu- mulation and subsequent signaling are an integral part of rhizobium LCO signaling remains elusive. Here, we show that cytokinin signaling is required for the majority of transcriptional changes induced by rhizo- bium LCOs. In addition, we demonstrate that several cytokinins accumulate in the root susceptible zone 3 h after rhizobium LCO application, including the biologically most active cytokinins, trans-zeatin and iso- pentenyl adenine. These responses are dependent on calcium- and calmodulin-dependent protein kinase （CCaMK）, a key protein in rhizobial LCO-induced signaling. Analysis of the ethylene-insensitive Mtein21 Mtsickle mutant showed that LCO-induced cytokinin accumulation is negatively regulated by ethylene. Together with transcriptional induction of ethylene biosynthesis genes, it suggests a feedback loop negatively regulating LCO signaling and subsequent cytokinin accumulation. We argue that cytokinin accumulation is a key step in the pathway leading to nodule organogenesis and that this is tightly controlled by feedback loops.Legume rhizobium symbiosis is initiated upon perception of bacterial secreted lipo-chitooligosaccharides （LCOs）. Perception of these signals by the plant initiates a signaling cascade that leads to nodule formation. Several studies have implicated a function for cytokinin in this process. However, whether cytokinin accu- mulation and subsequent signaling are an integral part of rhizobium LCO signaling remains elusive. Here, we show that cytokinin signaling is required for the majority of transcriptional changes induced by rhizo- bium LCOs. In addition, we demonstrate that several cytokinins accumulate in the root susceptible zone 3 h after rhizobium LCO application, including the biologically most active cytokinins, trans-zeatin and iso- pentenyl adenine. These responses are dependent on calcium- and calmodulin-dependent protein kinase （CCaMK）, a key protein in rhizobial LCO-induced signaling. Analysis of the ethylene-insensitive Mtein21 Mtsickle mutant showed that LCO-induced cytokinin accumulation is negatively regulated by ethylene. Together with transcriptional induction of ethylene biosynthesis genes, it suggests a feedback loop negatively regulating LCO signaling and subsequent cytokinin accumulation. We argue that cytokinin accumulation is a key step in the pathway leading to nodule organogenesis and that this is tightly controlled by feedback loops.

关 键 词：Medicago truncatula CYTOKININ ethylene RHIZOBIUM lipo-chitooligosaccharides CRE1 

分 类 号：S144.3[农业科学—肥料学] Q946.885[农业科学—农业基础科学]