Mechanistic studies of plant growth promotion by rhizosphere bacteria
Plant growth promoting bacteria (PGPB) colonize roots and engage in associative symbiosis with various host plants, including bioenergy grass species. These bacteria can reach quite high numbers (e.g., 108 CFU/gram fresh weight) but elicit no plant defense response. PGPB colonize both as epiphytes and also endophytes. While it is well established that specific rhizosphere bacteria have the ability to promote plant growth, the molecular mechanisms that underlie this ability are still poorly understood. In our laboratory, we are exploring both the bacterial and plant functions necessary for the establishment and efficacy of these beneficial plant-microbe interactions. We employ plant model systems such as Arabidopsis thaliana, Brachypodium distachyon and Setaria viridis to explore the transcriptional, proteomic and metabolic response to bacterial inoculation. For example, the data demonstrate a clear difference between the plant response to inoculation with wild-type bacteria and mutant strains unable to fix atmospheric nitrogen, emphasizing the impact of nitrogen fixation in these associations. We are also utilizing genome wide association analysis to define those specific plant alleles important for the plant response to bacterial colonization. With regard to the bacteria, we are using well-characterized PGPB, including Azoarcus olearius, Azospirillum brasilense, Herbaspirillum seropedicae, and Bacillus pumilis. As one approach, we conducted Tn-seq experiments to define those bacterial genes important for bacterial colonization of the rhizosphere. For example, these experiments identified genes involved in polyhydroxybutyrate (PHB) biosynthesis and catabolism as playing a crucial role in the ability of the bacteria to promote plant growth. In general, we do not find evidence for a strong role for phytohormone synthesis or response in the experiments we have conducted. The data suggest that the plant response to bacterial colonization is likely a multigenic, quantitative trait, which may vary significantly between genotypes of the plant host or bacterial partner.
Recent publications from the lab on this topic:
Beverly J. Agtuca, Sylwia A. Stopka, Thalita R. Tuleski, Fernanda P. do Amaral, Sterling Evans, Yang Liu, Dong Xu, Rose Adele Monteiro, David W. Koppenaal, Ljiljana Paša-Tolić, Christopher R. Anderton, Akos Vertes, and Gary Stacey (2019) In situ metabolomic analysis of Setaria viridis roots colonized by beneficial endophytic bacteria. Mol. Plant-Microbe Int. https://doi.org/10.1094/MPMI-06-19-0174-R
Caroline Kukolj, Fábio O. Pedrosa, Gustavo A. de Souza, Luciano F. Huergo, Glaucio Valdameri, Gary Stacey, Emanuel M. Souza (2019) Proteomic and metabolomic analysis of Azospirillum brasilense FP2 wild type and a ntrC mutant strain grown under high and low nitrogen conditions. J. Proteome Res. (in press) 10.1021/acs.jproteome.9b00397
Luis Paulo Silveira Alves, Fernanda Plucani do Amaral, Daewon Kim, Maritza Todo Bom, Manuel Piñero Gavídia, Cícero Silvano Teixeira, Fernanda Holthman, Fabio de Oliveira Pedrosa, Emanuel Maltempi de Souza, Leda Satie Chubatsu, Marcelo Müller-Santos, Gary Stacey (2019) Importance of poly-3-hydroxybutyrate (PHB) metabolism to the ability of Herbaspirillum seropedicae to promote plant growth. Appl. Environ. Microbiol. 85 (6): 5:e02586-18.; 10.1128/AEM.02586-18
Helisson Faoro, Rodrigo Rene Menegazzo, Federico Battistoni, Prasad Gyaneshwar, Fernanda P. do Amaral, Cecilia Taulé, Sydnee Rausch, Patricia Gonçalves Galvão, Cecilia de los Santos, Shubhajit Mitra, Gabriela Heijo, Shih-Yi Sheu, Wen-Ming Chen, Cintia Mareque, Michelle Zibetti Tadra-Sfeir, J. Ivo Baldani, Marta Maluk, Ana Paula Guimarães, Gary Stacey, Emanuel M. de Souza, Fabio O. Pedrosa, Leonardo Magalhães Cruz and Euan K. James. 2017. The oil-contaminated soil diazotroph Azoarcus olearius DQS-4T is genetically and phenotypically similar to the model grass endophytev Azoarcus sp. BH72. Environ. Microbiol. Rep. 9(3): 223-238. DOI: 10.1111/1758-2229.12502
Fernanda P. do Amaral, Vânia C. S. Pankievicz, Ana Carolina M. Arisi, Emanuel M. de Souza, Fabio Pedrosa, Gary Stacey (2016) Differential growth responses of Brachypodium distachyon genotypes to inoculation with plant growth promoting rhizobacteria. Plant Mol. Biol. 90: 689-697 10.1007/s11103-016-0449-8
Pankievicz, Vania C.S., Fernanda P. Amaral, Karina F. D. N. Santos, Beverly Agtuca, Youwen Xu, Michael J. Schueller, Ana Carolina M. Arisi, Maria. B.R. Steffens, Emanuel M. de Souza, Fabio O. Pedrosa, Richard A. Ferrieri and Gary Stacey (2014) Robust biological nitrogen fixation in a C4 model grass, Setaria viridis. Plant J. 81: 907-919. doi:10.1111/tpj.12777