Chapter Nine - Applications of transgenic approaches in developing an understanding of drought tolerance in poplar
Section snippets
The need for drought tolerant energy crops, including poplar
The current worldwide environment is facing significant challenges directly associated with increased release of heat-trapping greenhouse gases. These changes have not only resulted in areas with significant increases in the occurrences of drought, but predictions of long term increase in global mean temperatures (IPCC, 2014; Walsh et al., 2014). Moreover, if the trend continues, increases in global temperatures will result in changing precipitation patterns reflected in drought in certain
Agrobacterium transformations
Instrumental to genetic improvement of energy crops are applications of evolving biotechnology. These approaches pose significant opportunities for improvement of important agronomic traits of forest species including enhanced biomass production and drought and salt tolerance (for reviews: Dinneny et al., 2008; Dubouzet, Strabala, & Wagner, 2013; Polle, Janz, Teichmann, & Lipka, 2013; Wang, Cai, Xu, Wang, & Dai, 2016; Wang, Liu, et al., 2016; Yadav, Ayre, & Bush, 2015). Both forward and reverse
What transgenic technologies have revealed about drought tolerance in poplar
A number of recent reports describe efforts to enhance drought tolerance in poplar using GE technology. These reports reveal underlying biological factors and genetic contributions to this important trait. The reports summarized below focus on three major areas that contribute to this important phenotype in poplar: enhanced ability of drought resistant phenotypes to reduce the effects of drought-induced reactive oxygen species, ABA responses on stomatal behaviour and tissue patterning related
Nitrogen utilization in trees and the central role of glutamine synthetase
The availability of inorganic nitrogen in soils is often a limiting factor in plant growth and development. Most tree species grow in areas where nitrate and/or ammonium are the major forms of nitrogen available in soil (Wolt & Wolt, 1994).
One main difference between herbaceous and woody plants is the manner by which soil nitrate is assimilated. In many tree species the majority of nitrate taken up from soil is reduced in roots to ammonium by the action of both nitrate reductase (NR) and
The relationship between nitrogen assimilation and drought tolerance in hybrid poplar
Recognizing the importance of developing an understanding of drought tolerance, we have investigated mechanisms for enhanced drought tolerance observed in GS poplar in ecophysiological studies (El-Khatib et al., 2004; Molina-Rueda & Kirby, 2015; Molina-Rueda et al., 2013; Zhong et al., 2004). In comparison to leaves of WT controls, GS poplars maintain expression of fundamental enzymes (GS, GOGAT, and Rubisco) under water stress and during recovery. Overexpression of GS also sustained
Conclusions
An overview of the applications of genetic engineering approaches to develop an understanding of interacting roles of reduced nitrogen in conferring drought tolerance in poplar is presented. Overexpression of glutamine synthetase (GS) causes alterations to nitrogen metabolism including higher production of free amino acids including glutamine, glutamate, and GABA. In addition to contributing to enhanced growth, these metabolites can act as signals driving changes in expression of stress-related
Acknowledgements
We gratefully acknowledge the efforts of the laboratory of Dr. Chung Jui Tsai at the University of Georgia for patient collaboration on the poplar transcriptome analysis and expression network analysis.
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