title: The Symbiotic Performance of Chickpea Rhizobia Can Be Improved by Additional Copies of the clpB Chaperone Gene.
abstract: The ClpB chaperone is known to be involved in bacterial stress response. Moreover, recent studies suggest that this protein has also a role in the chickpea-rhizobia symbiosis. In order to improve both stress tolerance and symbiotic performance of a chickpea microsymbiont, the Mesorhizobium mediterraneum UPM-Ca36T strain was genetically transformed with pPHU231 containing an extra-copy of the clpB gene. To investigate if the clpB-transformed strain displays an improved stress tolerance, bacterial growth was evaluated under heat and acid stress conditions. In addition, the effect of the extra-copies of the clpB gene in the symbiotic performance was evaluated using plant growth assays (hydroponic and pot trials). The clpB-transformed strain is more tolerant to heat shock than the strain transformed with pPHU231, supporting the involvement of ClpB in rhizobia heat shock tolerance. Both plant growth assays showed that ClpB has an important role in chickpea-rhizobia symbiosis. The nodulation kinetics analysis showed a higher rate of nodule appearance with the clpB-transformed strain. This strain also induced a greater number of nodules and, more notably, its symbiotic effectiveness increased ~60% at pH5 and 83% at pH7, compared to the wild-type strain. Furthermore, a higher frequency of root hair curling was also observed in plants inoculated with the clpB-transformed strain, compared to the wild-type strain. The superior root hair curling induction, nodulation ability and symbiotic effectiveness of the clpB-transformed strain may be explained by an increased expression of symbiosis genes. Indeed, higher transcript levels of the nodulation genes nodA and nodC (~3 folds) were detected in the clpB-transformed strain. The improvement of rhizobia by addition of extra-copies of the clpB gene may be a promising strategy to obtain strains with enhanced stress tolerance and symbiotic effectiveness, thus contributing to their success as crop inoculants, particularly under environmental stresses. This is the first report on the successful improvement of a rhizobium with a chaperone gene.
authors: ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas (Laboratório de Microbiologia do Solo), Universidade de Évora, Núcleo da Mitra, Ap. 94, 7002-554, Évora, Portugal.
authors: Ana
authors: A
authors: Paço
authors: ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas (Laboratório de Microbiologia do Solo), Universidade de Évora, Núcleo da Mitra, Ap. 94, 7002-554, Évora, Portugal.|IIFA-Instituto de Investigação e Formação Avançada, Universidade de Évora, Ap. 94, 7002-554, Évora, Portugal.
authors: Clarisse
authors: C
authors: Brígido
authors: ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas (Laboratório de Microbiologia do Solo), Universidade de Évora, Núcleo da Mitra, Ap. 94, 7002-554, Évora, Portugal.|IIFA-Instituto de Investigação e Formação Avançada, Universidade de Évora, Ap. 94, 7002-554, Évora, Portugal.
authors: Ana
authors: A
authors: Alexandre
authors: Departamento de Microbiología y Genética, Centro Hispano Luso de Investigaciones Agrarias, Universidad de Salamanca, 37007, Salamanca, Spain.
authors: Pedro F
authors: PF
authors: Mateos
authors: ICAAM-Instituto de Ciências Agrárias e Ambientais Mediterrânicas (Laboratório de Microbiologia do Solo), Universidade de Évora, Núcleo da Mitra, Ap. 94, 7002-554, Évora, Portugal.
authors: Solange
authors: S
authors: Oliveira
mesh_terms: D000217:Acyltransferases / Q000096:biosynthesis; D000581:Amidohydrolases / Q000096:biosynthesis; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D029863:Cicer / Q000382:microbiology*; D018628:Gene Dosage / Q000235:genetics*; D006360:Heat-Shock Proteins / Q000235:genetics*; D018869:Heat-Shock Response; D059128:Mesorhizobium / Q000235:genetics*; D018832:Molecular Chaperones / Q000235:genetics*; D017351:N-Acetylglucosaminyltransferases / Q000235:genetics; D055170:Plant Root Nodulation / Q000235:genetics; D053204:Root Nodules, Plant / Q000378:metabolism; D013312:Stress, Physiological / Q000235:genetics; D013559:Symbiosis / Q000235:genetics; D014170:Transformation, Genetic / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C073606:nodB protein, Bacteria; D000217:Acyltransferases; C060770:NodA protein, Rhizobiales; D017351:N-Acetylglucosaminyltransferases; C060771:NodC protein, Rhizobiales; D000581:Amidohydrolases