The Rhizobium etli RpoH1 and RpoH2 sigma factors are involved in different stress responses.
The physiological role and transcriptional expression of Rhizobium etli sigma factors rpoH1 and rpoH2 are reported in this work. Both rpoH1 and rpoH2 were able to complement the temperature-sensitive phenotype of an Escherichia coli rpoH mutant. The R. etli rpoH1 mutant was sensitive to heat shock, sodium hypochlorite and hydrogen peroxide, whereas the rpoH2 mutant was sensitive to NaCl and sucrose. The rpoH2 rpoH1 double mutant had increased sensitivity to heat shock and oxidative stress when compared with the rpoH1 single mutant. This suggests that in R. etli, RpoH1 is the main heat-shock sigma factor, but a more complete protective response could be achieved with the participation of RpoH2. Conversely, RpoH2 is involved in osmotic tolerance. In symbiosis with bean plants, the R. etli rpoH1 and rpoH2 rpoH1 mutants still elicited nodule formation, but exhibited reduced nitrogenase activity and bacterial viability in early and late symbiosis compared with nodules produced by rpoH2 mutants and wild-type strains. In addition, nodules formed by R. etli rpoH1 and rpoH2 rpoH1 mutants showed premature senescence. It was also determined that fixNf and fixKf expression was affected in rpoH1 mutants. Both rpoH genes were induced under microaerobic conditions and in the stationary growth phase, but not in response to heat shock. Analysis of the upstream region of rpoH1 revealed a sigma70 and a probable sigmaE promoter, whereas in rpoH2, one probable sigmaE-dependent promoter was detected. In conclusion, the two RpoH proteins operate under different stress conditions, RpoH1 in heat-shock and oxidative responses, and RpoH2 in osmotic tolerance.
Martínez-Salazar
Jaime M
JM
Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Sandoval-Calderón
Mario
M
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Guo
Xianwu
X
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Castillo-Ramírez
Santiago
S
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Reyes
Alma
A
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Loza
Maria G
MG
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Rivera
Javier
J
Programa de Ingeniería Genómica, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Alvarado-Affantranger
Xochitl
X
Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apartado Postal 510-3, CP 62271 Cuernavaca, Morelos, México.
Sánchez
Federico
F
Departamento de Biología Molecular de Plantas, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Apartado Postal 510-3, CP 62271 Cuernavaca, Morelos, México.
González
Víctor
V
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Dávila
Guillermo
G
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
Ramírez-Romero
Miguel A
MA
Programa de Genómica Evolutiva, Centro de Ciencias Genómicas, Universidad Nacional Autónoma de México, Apartado Postal 565-A, CP 62210 Cuernavaca, Morelos, México.
D001483:Base Sequence; D007887:Fabaceae / Q000382:microbiology / Q000502:physiology; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018869:Heat-Shock Response; D008969:Molecular Sequence Data; D009154:Mutation; D009997:Osmotic Pressure; D018384:Oxidative Stress; D011401:Promoter Regions, Genetic; D042163:Rhizobium etli / Q000235:genetics / Q000502:physiology*; D053204:Root Nodules, Plant / Q000382:microbiology / Q000502:physiology; D012808:Sigma Factor / Q000235:genetics / Q000378:metabolism*; D013312:Stress, Physiological; D013559:Symbiosis
D006360:Heat-Shock Proteins; D012808:Sigma Factor; C069774:heat-shock sigma factor 32