Cisgenesis represents a step toward a new generation of GM crops. The lack of selectable genes (e.g. antibiotic or herbicide resistance) in the final product and the fact that the inserted gene(s) derive from organisms sexually compatible with the target crop should rise less environmental concerns and increase consumer’s acceptance6. The generation of a cisgenic apple plant by inserting the endogenous apple scab resistance gene Homologues of Cladosporium fulvum resistance genes of Vf region (HcrVf2) under the control of its own regulatory sequences into the scab susceptible apple cultivar Gala2. In order to develop marker-free plants, the chemically inducible recombinase system in strawberry was applied to apple.

The linkage-drag-free cisgenic approach is highly attractive, and embodies the possibility to stack resistance genes from different sources, even if they originate from the same chromosomal position in different species or accessions, as described for Phytophthora- resistant potato using R & Avr genes.

Cisgenesis can be used to enhance the expression of an endogenous phy¬tase gene in barley through the insertion of extra gene cop¬ies of the endogenous phytase gene isolated from barley itself. Phytases of the purple acid phosphatase (PAPhy’s) group account for the majority of the phytases synthesized in barley. Two PAPhy types, termed HvPAPhy_a and HvPAPhy_b, have been identified. HvPAPhy_a is preferentially synthesized during seed de¬velopment and stored as preformed phytase in the mature grain, while HvPAPhy_bis preferentially synthesized dur¬ing germination.

Gibberellic acid is a plant hormone with a wide variety of functions in controlling plant growth and development. Five different cisgenes (GA20ox7, GA2ox2, GAI1, RGL 1_1, and RGL 1_2) were studied, along with empty vector controls and non-transgenic con¬trols. GA20ox is an enzyme that catalyzes the penultimate step in the biosynthetic GA pathway, and thus tends to promote cell division and elongation, whereas the other genes tend to repress or attenuate active GA actions (GA degradation by GA2ox2; the other genes were DELLA domain proteins that attenuate GA signals).

References:

1. Han K, Dharmawardhana P., Arias R., Ma C, Busov V., and Strauss S., 2010, Gibberellin-associated cisgenes modify growth, stature and wood properties in Populus. Plant BiotechnolJ.Online version available from http://onlinelibrary.wiley.com/doi/10.1111/j.1467-7652.2010.00537.x/pdf.

2. Holme IB, Dionisio G, Brinch-Pedersen H, Wendt T, Madsen CK, Vincze E and Holm PB.,2012, Cisgenicbarley with improved phytase activity. Plant Biotechnol. J.,10, 237-247

3. Jacobsen, E. and Hutten, R., 2006, Stacking resistance genes in potato by cisgenesis instead of introgression breeding. In Potato Developments in a Changing Europe (Haase, N.U. and Haverkort, A.J., eds), pp. 46–57, Wageningen Academic Publishers.

4. Schaart, J.G., Krens, F.A., Pelgrom, K.T.B., Mendes, O., Rouwendal, G.J.A., 2004, Effective production of marker-free transgenic strawberry plants using inducible site-specific recombination and a bifunctional selectable marker gene. Plant Biotechnology J., 2, 233–240.

5. ThaliaVanblaerea, Iris Szankowskia, Jan Schaartb, HenkSchoutenb, HenrykFlachowskyGiovanni A.L. Broggini, CesareGessler., 2011, The development of a cisgenic apple. Plant Journal of Biotechnology,154,304-311

6. Schouten, H.J., Krens, F.A., Jacobsen, E., 2006, Do cisgenic plants warrant less stringent oversight? Nature Biotechnology,24, 753.