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Q:
Are genetic manipulation (GM) techniques too crude and inexact to enable the cutting and pasting of complex multi-genic traits such as nitrogen fixation in grains, drought tolerance and salt tolerance into crop plants? As Dr Richard Richards of Australian CSIRO Plant Industry says: “GM technologies are generally only suitable for the single gene traits, not complex multigenic ones.” And Dr Clive James of ISAAA says: “Drought tolerance is an infinitely more complex trait than herbicide tolerance and insect resistance (which are single gene traits) and progress is likely to be on a step by step basis.”
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A:Expert Answer

Generally speaking, complex traits are more difficult to manipulate than simple traits like herbicide resistance. However, it has been repeatedly shown that by manipulating the expression of regulatory genes or signaling proteins, one can control entire developmental or metabolic pathways that control complex traits. Dr. James is somewhat correct that drought tolerance is more complex than herbicide resistance, but researchers have been successfully engineering plants for drought tolerance by manipulating developmental and metabolic pathways (see references, below). This strategy has been used for more than a decade (Kasuga et al., 1999). For example, Li et al. (2014) showed that expressing a stress-responsive transcription factor in tobacco led to increased tolerance to a variety of stresses, including drought. Expressing genes that control the synthesis of osmoprotectants, like various sugars or sugar alcohols, can also lead to drought tolerance (Romero et al., 1997; Yeo et al., 2000). These few examples show that turning on specific developmental or metabolic pathways could get around the problem of complex traits being controlled by many different genes.

 

Of course, trying to get all the genes necessary for nitrogen fixation into corn would be quite an undertaking, but much progress is being made on manipulating large pieces of DNA that contain many genes (Karas et al., 2013, 2014). A few decades ago, the thought of being able to construct artificial chromosomes was crazy, but now it is routine to construct artificial chromosome for bacteria and yeast. How long before it is not so crazy to construct an artificial chromosome for plants?

 

With regard to the relative crudeness of GM techniques, there are a few new game-changing technologies that allow targeted introduction of desired sequences into genomes (Sampson et al., 2014; Carroll, 2014; Mussolino et al., 2012). These techniques will allow the more precise editing of genes and complexes of genes.

References:

 

Carroll, D. 2014. Genome Engineering with Targetable Nucleases. Annu. Rev. Biochem. 83:

Karas, B.J., B. Molparia, J. Jablanovic, W.J. Hermann, Y.C. Lin, C.L. Dupont, C. Tagwerker, I.T. Yonemoto, V.N. Noskov, R.Y. Chuang, A.E. Allen, J.I. Glass, C.A. Hutchison, H.O. Smith, J.C. Venter and P.D. Weyman. 2013. Assembly of eukaryotic algal chromosomes in yeast. J Biol Eng 7: 30.

 

Karas, B.J., J. Jablanovic, E. Irvine, L. Sun, L. Ma, P.D. Weyman, D.G. Gibson, J.I. Glass, J.C. Venter, C.A. Hutchison, H.O. Smith and Y. Suzuki. 2014. Transferring whole genomes from bacteria to yeast spheroplasts using entire bacterial cells to reduce DNA shearing. Nat Protoc 9: 743-750.

 

Kasuga, M., Q. Liu, S. Miura, K. Yamaguchi-Shinozaki and K. Shinozaki. 1999. Improving plant drought, salt, and freezing tolerance by gene transfer of a single stress-inducible transcription factor. Nat. Biotechnol. 17: 287-291.

 

Li, X., D. Zhang, H. Li, Y. Wang, Y. Zhang and A.J. Wood. 2014. EsDREB2B, a novel truncated DREB2-type transcription factor in the desert legume Eremosparton songoricum, enhances tolerance to multiple abiotic stresses in yeast and transgenic tobacco. BMC Plant Biol. 14: 44.

 

Liu, G., X. Li, S. Jin, X. Liu, L. Zhu, Y. Nie and X. Zhang. 2014. Overexpression of Rice NAC Gene SNAC1 Improves Drought and Salt Tolerance by Enhancing Root Development and Reducing Transpiration Rate in Transgenic Cotton. PLoS ONE 9: e86895.

 

Mussolino, C. and T. Cathomen. 2012. TALE nucleases: tailored genome engineering made easy. Curr. Opin. Biotechnol. 23: 644-650.

 

Romero, C., J.M. Belles, J.L. Vaya, R. Serrano and F.A. Culianez-Macia. 1997. Expression of the yeast trehalose-6-phosphate synthase gene in transgenic tobacco plants: pleiotropic phenotypes include drought tolerance. Planta 201: 293-297.

 

Sampson, T.R. and D.S. Weiss. 2014. Exploiting CRISPR/Cas systems for biotechnology. BioEssays 36: 34-38.

 

Su, L.T., J.W. Li, D.Q. Liu, Y. Zhai, H.J. Zhang, X.W. Li, Q.L. Zhang, Y. Wang and Q.Y. Wang. 2014. A novel MYB transcription factor, GmMYBJ1, from soybean confers drought and cold tolerance in Arabidopsis thaliana. Gene 538: 46-55.

 

Yeo, E.T., H.B. Kwon, S.E. Han, J.T. Lee, J.C. Ryu and M.O. Byu. 2000. Genetic engineering of drought resistant potato plants by introduction of the trehalose-6-phosphate synthase (TPS1) gene from Saccharomyces cerevisiae. Mol Cells 10: 263-268.

 

Yoshiba, Y., T. Kiyosue, K. Nakashima, K. Yamaguchi-Shinozaki and K. Shinozaki. 1997. Regulation of levels of proline as an osmolyte in plants under water stress. Plant Cell Physiol. 38: 1095-1102.

 

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