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Discuss the evidence showing that the two types of plant-microbe symbiosis, nitrogen-fixing root nodule development and arbuscular mycorrhiza formation, are controlled by common genetic determinates in the host plant.


Leguminous plant roots form endosymbioses with both bacteria and fungi forming nitrogen-fixing root nodules and arbuscular mycorrhiza (AM), respectively. The physiological outcomes of both symbioses are quite dissimilar, however, several studies have shown that nodulation defective mutant are often defective in arbuscular mycorrhiza formation, this is indicative of a common genetic overlap in perception of endosymbiosis signals in the host. Analysis has shown several genes to integral to this common system. Study of common phenotypic markers, such as calcium spiking and early nodulation gene expression, has helped to order the action of the common symbiosis genes. The recent cloning of a novel receptor like-kinase has confirmed its role in transduction of both bacterial and fungal symbiotic signals. The evolutionary history of AM-host interactions dates back ~450 MYA, and it is thought the more recent rhizobia-legume interaction may have evolved by recruiting plant fac...

Posted by: Helene Hannah

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