Unraveling the secret of bacterial success on plant surfaces


Demonstrate the beauty of genetics

Dr Xue-Xian Zhang

Institute of Molecular Biosciences & NZ Institute for Advanced Study, Massey University, Private Bag 102 904, Auckland, New Zealand

E-mail: xxzhang1@gmail.com 

 
 
Like humans, the health and well being of plants is to a large extent determined by the microbes with which they co-exist.  While some bacteria are harmful, others have the capacity to promote plant growth.   I am interested in the biology of Pseudomonas fluorescens SBW25 – a bacterium that can promote plant growth.  One of the most significant challenges that we face is in understanding the function of P. fluorescens in the plant environment. If P. fluorescens was the size of a bird and possessed similar morphological complexity then progress could be made by observation alone. In the absence of readily observable phenotypes we have taken to detecting changes in patterns of gene expression.  Genes expressed in one environment, but not in another are likely to encode traits relevant to the former environment, but not the latter.  Understanding the biological significance of these traits and their contribution to ecological performance is our primary aim.  Accordingly, much of my current research concerns the regulation, biological function and ecological significance of plant-inducible genes from P. fluorescens SBW25.

Selected publications

Xue-Xian Zhang and Paul B. Rainey (2007) Genetic analysis of the histidine utilization (hut) genes in Pseudomonas fluorescens SBW25. Genetics 176: 2165-2176.

Xue-Xian Zhang and Paul B. Rainey (2007) The role of a P1-type ATPase from Pseudomonas fluorescens SBW25 in copper homeostasis and plant colonization. Molecular Plant-Microbe Interactions 20: 581-588.

 List of Publications

The following are projects under my current investigation, together with Prof. Paul B Rainey: 

 

Population genetics of plant-associated Pseudomonas in terms of histidine/urocanate utilization

Making a living in any environment is dependent upon obtaining an adequate supply of nutrients.  Amino acids, such as histidine, can provide carbon, nitrogen, and a source of energy.  The differences among different Pseudomonas strains in their capacity to take up and metabolize histidine and urocanate are of particular inertests.  The suspicion is that differences in uptake systems among different strains may be a major determinant of ecological success.

 

The role of a unique two component regulatory system (CbrAB) in global carbon and nitrogen metabolism.

Not surprisingly, bacteria need to monitor their environment in terms of the availability of nutrients.  We have shown that the CbrAB system plays an important role in controlling the overall activity of genes involved in extracting carbon, nitrogen and energy from a range of organic compounds.  Current efforts are focused in understanding how CbrA senses its environment (it is among other things capable of transporting amino acids) and how CbrB co-ordinates its transcriptional activities with other regulators that are also responsive to the carbon:nitrogen ratio. We are also interesting in the molecular mechanisms of carbon catabolite repression in Pseudomonas and the possible involvement of CbrAB will be investigated.

 

Molecular mechanisms of copper homeostasis in Pseudomonas fluorescens SBW25.

Copper is a necessary metal, but it is also toxic.  We recently characterized a copper transporter system (CueA) in P. fluorescens SBW25 that plays a role in bacterial competitive colonization in planta. Our primary interests are in the regulation of this system. Other copper-balancing proteins are also being characterized with a focus on a copper chaperonic protein CopZ.