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The deubiquitinating enzyme AMSH1 is required for rhizobial infection and nodule organogenesis in Lotus japonicus

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The legume-rhizobium symbiosis contributes large quantities of fixed nitrogen to both agricultural and natural ecosystems. This global impact and the selective interaction between rhizobia and legumes culminating in development of functional root nodules have motivated detailed studies of the underlying mechanisms. We conducted a screen for aberrant nodulation phenotypes using the Lotus japonicus LORE1 insertion mutant collection. Here, we describe the identification of amsh1 mutants that only develop small nodule primordia and display stunted shoot growth, and show that the aberrant nodulation phenotype caused by LORE1 insertions in the Amsh1 gene can be separated from the shoot phenotype. In amsh1 mutants, rhizobia initially became entrapped in infection threads with thickened cells walls. Much delayed, some rhizobia were released into plant cells, however no typical symbiosome structures were formed. Furthermore, cytokinin treatment only very weakly induced nodule organogenesis in amsh1 mutants, suggesting that AMSH1 function is required downstream of cytokinin signaling. Biochemical analysis showed that AMSH1 is an active deubiquitinating enzyme and that AMSH1 specifically cleaves K63-linked ubiquitin chains. Post-translational ubiquitination and deubiquitination processes comprising the AMSH1 deubiquitinating enzyme are thus involved in both infection and organogenesis in Lotus japonicus. This article is protected by copyright. All rights reserved.

Original languageEnglish
JournalPlant Journal
Pages (from-to)719-731
Number of pages13
Publication statusPublished - 28 Jun 2015

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