Molecular Analysis of Legume Nodule Development and Autoregulation

Abstract

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.

Root-derived CLE glycopeptides control nodulation by direct binding to HAR1 receptor kinase

“…This symbiosis enables nitrogen fixation in the nodules and is beneficial to the host plants; however, excessive nodule formation is deleterious to the plants because the energy cost outweighs the need for fixed nitrogen. To achieve a balance in this symbiotic relationship, the host plant tightly controls the number of nodules via a root-to-shoot-to-root negative feedback signalling loop commonly termed autoregulation of nodulation [1][2][3][4] .…”

Integrated Management and Host Plant Resistance Against Dry Root Rot [Macrophomina phaseolina (Tassi.) Goid] of Chickpea

“…Gram considered as the World's second most widely grown legume after beans (Phaseolus vulgaris). Its ability to form nitrogen-fixing nodules via interaction with rhizobia adds to its uniqueness which make it's a valuable crop for maintaining soil fertility (Ferguson et al, 2010). India is the largest producer and consumer of pulses in the world.…”

Molecular characterisation of flowering genes in Pongamia Pinnata

“…This enables them to obtain ammonia by converting nitrogen gas (N 2 ) in the atmosphere to ammonia, which is essential for nucleotide and protein synthesis, and general metabolism process (Ferguson et al, 2010;Samuel et al, 2013). Currently, a lot of fossil fuel is required in the production (Haber-Bosch process) and delivery of these nitrogen fertilisers.…”

“…Pongamia is highly tolerant against salt and drought and can grow on malnourished land, thereby averting the food versus fuel debate and eliminating competition for the resources needed for food production. Moreover, pongamia trees are able to form symbiotic relationships with the nitrogen-fixing rhizobia and myrcorrhizal fungi, therefore enabling them to convert nitrogen gas to ammonia and improving their capacity to absorb water and mineral uptake, respectively (Scheublin et al, 2004;Bonfante and Genre, 2010;Ferguson et al, 2010;Samuel et al, 2013).…”

“…Consequently, lower costs and lesser amount of fossil energy will be used, benefitting both the environment and economy. In addition, fertiliser-associated pollution such as eutrophication can also be reduced (Ferguson et al, 2010;Jensen et al, 2012).…”