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Title: Characterization of Three Genes Located in a 4.0-KB Fragment Within the MID Gene Cluster of Rhizobium SP Strain TAL1145 
Author: Anamizu, Joy N.P.
Date: 2002-12
Publisher: University of Hawaii at Manoa
Abstract: Rhizobium sp. strain TAL1145 is a soil bacterium that forms nitrogen-fixing root nodules on the tree-legume, Leucaena leucocephala. Leucaena produces a toxic non-protein amino acid, known as mimosine, which is also released in root exudates. Rhizobium sp. TAL1145 can degrade mimosine and use it as a source of carbon and nitrogen. The genes for mimosine degradation (mid genes) in TAL1145 have been recently isolated. The mid genes are located in two clusters within a 25-kb DNA fragment in the TAL1145 chromosome. The aim of this investigation is to identify and characterize the genes in a 4.0-kb EcoRI fragment nestled between the mid and pyd gene clusters and to determine their role in mimosine degradation and symbiosis. Sequencing of this fragment showed four open reading frames (ORFs). ORF1 is 503 bp long and it may encode a 17.6-kDa protein of unknown function. The ORF2-encoded protein may be a 1-aminocyclopropane-1-carboxylate deaminase (ACC demaminase), which might be involved in converting ACC sequestered from plants into ammonia and a-ketobutyrate. ACC is a precursor in the synthesis of ethylene by plant roots. By degrading ACC, the enzyme ACC deaminase may reduce ethylene production in the plant root system. The ORF3- and ORF4-encoded proteins have high homology with the small and large subunits of alkyl hydroperoxide reductase of several organisms. These proteins may be involved in protecting Rhizobium from oxidative damage during growth in the soil environment. Knockout mutants of TAL1145 were isolated by Tn3Hogus transposon insertion into ORF2 and ORF4. Results of this study indicate that these genes are not involved in mimosine degradation. However, the role of Rhizobium sp. TAL1145 may not be limited to just a symbiotic nitrogen fixer, but may also enhance root development in Leucaena by inhibiting ethylene production.
Description: ix, 90 leaves
Rights: All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.

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