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....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.展开更多
Most land plants rely on the symbiosis with arbuscular mycor- rhizal (AM)fungi to acquire sufficient mineral nutrients from soils. Plants host AM fungi inside root cortex cells,where the fungus forms highly branched s...Most land plants rely on the symbiosis with arbuscular mycor- rhizal (AM)fungi to acquire sufficient mineral nutrients from soils. Plants host AM fungi inside root cortex cells,where the fungus forms highly branched structures called arbuscules.Arbuscules are surrounded by a specialized host membrane across which nutrients are exchanged in a cooperative manner.In return for mineral nutrients,the fungus obtains sugars and fatty acids from the plant (Luginbuehl and Oldroyd,2017).展开更多
In the late 19th century,it was discovered that legumes can establish a root nodule endosymbiosis with nitrogen-fixing rhizobia.Soon after,the question was raised whether it is possible to transfer this trait to non-l...In the late 19th century,it was discovered that legumes can establish a root nodule endosymbiosis with nitrogen-fixing rhizobia.Soon after,the question was raised whether it is possible to transfer this trait to non-leguminous crops.In the past century,an ever-increasing amount of knowledge provided unique insights into the cellular,molecular,and genetic processes controlling this endosymbiosis.In addition,recent phylogenomic studies uncovered several genes that evolved to function specifically to control nodule formation and bacterial infection.However,despite this massive body of knowledge,the long-standing objective to engineer the nitrogen-fixing nodulation trait on nonleguminous crop plants has not been achieved yet.In this review,the unsolved questions and engineering strategies toward nitrogen-fixing nodulation in non-legume plants are discussed and highlighted.展开更多
文摘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.
文摘Most land plants rely on the symbiosis with arbuscular mycor- rhizal (AM)fungi to acquire sufficient mineral nutrients from soils. Plants host AM fungi inside root cortex cells,where the fungus forms highly branched structures called arbuscules.Arbuscules are surrounded by a specialized host membrane across which nutrients are exchanged in a cooperative manner.In return for mineral nutrients,the fungus obtains sugars and fatty acids from the plant (Luginbuehl and Oldroyd,2017).
基金This work was supported by the ENSA project funded by the Bill&Melinda Gates Foundation to the University of Cambridge to R.G.No conflict of interest declared.
文摘In the late 19th century,it was discovered that legumes can establish a root nodule endosymbiosis with nitrogen-fixing rhizobia.Soon after,the question was raised whether it is possible to transfer this trait to non-leguminous crops.In the past century,an ever-increasing amount of knowledge provided unique insights into the cellular,molecular,and genetic processes controlling this endosymbiosis.In addition,recent phylogenomic studies uncovered several genes that evolved to function specifically to control nodule formation and bacterial infection.However,despite this massive body of knowledge,the long-standing objective to engineer the nitrogen-fixing nodulation trait on nonleguminous crop plants has not been achieved yet.In this review,the unsolved questions and engineering strategies toward nitrogen-fixing nodulation in non-legume plants are discussed and highlighted.
