Legumes are highly important food, feed and biofuel crops. With few exceptions, they can enter into an intricate symbiotic relationship with specific soil bacteria called rhizobia. This interaction results in the form...Legumes are highly important food, feed and biofuel crops. With few exceptions, they can enter into an intricate symbiotic relationship with specific soil bacteria called rhizobia. This interaction results in the formation of a new root organ called the nodule in which the rhizobia convert atmospheric nitrogen gas into forms of nitrogen that are useable by the plant. The plant tightly controls the number of nodules it forms, via a complex root-to-shoot-to-root signaling loop called autoregulation of nodulation （AON）. This regulatory process involves peptide hormones, receptor kinases and small metabolites. Using modern genetic and genomic techniques, many of the components required for nodule formation and AON have now been isolated. This review addresses these recent findings, presents detailed models of the nodulation and AON processes, and identifies gaps in our understanding of these process that have yet to be fully explained.展开更多
A variety of genes involved in nodule development and function were induced during sym biotic root nodule development in alfalfa. We identi fied those genes by comparing the cDNA-amplified fragment length polymorphism...A variety of genes involved in nodule development and function were induced during sym biotic root nodule development in alfalfa. We identi fied those genes by comparing the cDNA-amplified fragment length polymorphism (cDNA-AFLP) pat terns of infected nodules and uninfected roots. Sev enty-one transcript-derived fragments (TDFs) were isolated from about 3000 TDFs, which are enhanced or specifically expressed in nodule. The differentia expression patterns of 61 genes were confirmed b reverse Northern hybridization or Northern hybridiza tion analyses. Among these, 31 exhibited significan similarities to characterized database entries. These results suggest that the genes corresponding to the 31 TDFs may play important roles in signal transduc tion, gene expression and regulation, substance transportation or auto-regulation of nodulation during nodule development. The Northern hybridization analysis also indicates that the gene corresponding to TDF RX89 was not expressed in the nodule elic ited by bacA mutant, presumably it is specially in duced at the stage of nodule development when bacteroids begin to be differentiated.展开更多
Rhizobia interact with host legumes to induce the formation of nitrogen-fixing nodules,which is very important in agriculture and ecology.The development of nitrogen-fixing nodules is stringently regulated by host pla...Rhizobia interact with host legumes to induce the formation of nitrogen-fixing nodules,which is very important in agriculture and ecology.The development of nitrogen-fixing nodules is stringently regulated by host plants and rhizobial symbionts.In our previous work,a new Sinorhizobium meliloti LysR regulator gene(lsrB)was identified to be essential for alfalfa nodulation.However,how this gene is involved in alfalfa nodulation was not yet understood.Here,we found that this gene was associated with prevention of premature nodule senescence and abortive bacteroid formation.Heterogeneous deficient alfalfa root nodules were induced by the in-frame deletion mutant of lsrB(lsrB1-2),which was similar to the plasmid-insertion mutant,lsrB1.Irregular senescence zones earlier appeared in these nodules where bacteroid differentiation was blocked at different stages from microscopy observations.Interestingly,oxidative bursts were observed in these nodules by DAB staining.The decreased expression of lipopolysaccharide core genes(lpsCDE)was correspondingly determined in these nodules.S.meliloti lipopolysaccharide is required for suppression of oxidative bursts or host cell defense.These findings demonstrate that the S.meliloti lsrB gene is involved in alfalfa root nodule development and bacteroid differentiation by suppressing oxidative bursts or defense responses in host cells.展开更多
基金the Australian Research Council for Centre of Excellence funding
文摘Legumes are highly important food, feed and biofuel crops. With few exceptions, they can enter into an intricate symbiotic relationship with specific soil bacteria called rhizobia. This interaction results in the formation of a new root organ called the nodule in which the rhizobia convert atmospheric nitrogen gas into forms of nitrogen that are useable by the plant. The plant tightly controls the number of nodules it forms, via a complex root-to-shoot-to-root signaling loop called autoregulation of nodulation （AON）. This regulatory process involves peptide hormones, receptor kinases and small metabolites. Using modern genetic and genomic techniques, many of the components required for nodule formation and AON have now been isolated. This review addresses these recent findings, presents detailed models of the nodulation and AON processes, and identifies gaps in our understanding of these process that have yet to be fully explained.
文摘A variety of genes involved in nodule development and function were induced during sym biotic root nodule development in alfalfa. We identi fied those genes by comparing the cDNA-amplified fragment length polymorphism (cDNA-AFLP) pat terns of infected nodules and uninfected roots. Sev enty-one transcript-derived fragments (TDFs) were isolated from about 3000 TDFs, which are enhanced or specifically expressed in nodule. The differentia expression patterns of 61 genes were confirmed b reverse Northern hybridization or Northern hybridiza tion analyses. Among these, 31 exhibited significan similarities to characterized database entries. These results suggest that the genes corresponding to the 31 TDFs may play important roles in signal transduc tion, gene expression and regulation, substance transportation or auto-regulation of nodulation during nodule development. The Northern hybridization analysis also indicates that the gene corresponding to TDF RX89 was not expressed in the nodule elic ited by bacA mutant, presumably it is specially in duced at the stage of nodule development when bacteroids begin to be differentiated.
基金supported by National Basic Research Program of China (2010CB126501, 2011CB100702)the National Natural Science Foundation of China (31070218)
文摘Rhizobia interact with host legumes to induce the formation of nitrogen-fixing nodules,which is very important in agriculture and ecology.The development of nitrogen-fixing nodules is stringently regulated by host plants and rhizobial symbionts.In our previous work,a new Sinorhizobium meliloti LysR regulator gene(lsrB)was identified to be essential for alfalfa nodulation.However,how this gene is involved in alfalfa nodulation was not yet understood.Here,we found that this gene was associated with prevention of premature nodule senescence and abortive bacteroid formation.Heterogeneous deficient alfalfa root nodules were induced by the in-frame deletion mutant of lsrB(lsrB1-2),which was similar to the plasmid-insertion mutant,lsrB1.Irregular senescence zones earlier appeared in these nodules where bacteroid differentiation was blocked at different stages from microscopy observations.Interestingly,oxidative bursts were observed in these nodules by DAB staining.The decreased expression of lipopolysaccharide core genes(lpsCDE)was correspondingly determined in these nodules.S.meliloti lipopolysaccharide is required for suppression of oxidative bursts or host cell defense.These findings demonstrate that the S.meliloti lsrB gene is involved in alfalfa root nodule development and bacteroid differentiation by suppressing oxidative bursts or defense responses in host cells.
