Transgenic Sunflower - Genetics, Genomics and Breeding of Crop Plants - page 289

5-enolpyruvylshikimate-3-phosphate (EPSPS) enzyme. RR soybean was
obtained through expression of a gene coding for an EPSPS enzyme variant
from Agrobacterium tumefaciens , insensitive to GL herbicide, inserted by the
GTS 40-3-2 event of the same company. It has been available to farmers since
1994-95 in the US, Canada, Japan, and Argentina (Brookes and Barfoot
2006). In the latter case, soybean acreage increased by 10% per year during
the first decade and the GM varieties almost reached 100%. This increase
was reinforced because it facilitated zero-till practices, enhancing harvest
security of the double-crop system (wheat- soybean) and soybean production
in less favorable areas (Trigo and Cap 2006). In the US, adoption rate was
lower because it did not impact so strongly on the farmers' economic profit,
but allowed obtaining an “extra-farm” income due to the simplicity and
flexibility of the applied technology (Fernandez-Cornejo et al. 2006).
9.3 Genetic Modification of Sunflower
9.3.1 Early Transformation Methods
Sunflower has been considered as a recalcitrant species to genetic
transformation. Despite the lack of an efficient protocol, more than 40
publications have reported success in obtaining transgenic sunflower plants
and many field experiments have been performed. The first transgenic
sunflower was obtained by Everett et al. (1987) from hypocotyl-derived callus
that also produced transgenic shoots through disarmed Agrobacterium
tumefaciens plasmids. Even though weak and stunted, the transformed plants
produced pollen and were identical to the wild type plants of the original
inbred line.
Early efforts in sunflower biotechnology included embryo rescue,
somatic cell fusion, plant regeneration by direct or indirect organogenesis
and embryogenesis from explants, gynogenesis and anther culture (Friedt
1992; Alibert et al. 1994). Chimeric expression of genes was achieved earlier,
but recovery of transformed plants from protoplasts remained very difficult
until Schrammeijer et al. (1990) succeeded in meristem transformation from
split embryonic axes of immature embryos. Since then, sunflower
transformation based on microprojectile bombardment of half shoot apices
aimed to increase the bacterial infection, in combination with A. tumefaciens
co-culture and kanamycin as a selective agent (Bidney et al. 1992; Knittel et
al. 1994; Malone-Schoneberg et al. 1994; Grayburn and Vick 1995; Laparra
et al. 1995; Burrus et al. 1996; Lucas et al. 2000). Biolistic (DNA-coated
particle bombardment) efficiency highly relied on the plant material (Hunold
et al. 1995). Modifications for improving transgene efficiency, included
selectable markers (Escandon and Hahne 1991; Müller et al. 2001), pectinase
treatment of explants (Alibert et al. 1999), dehydration and rehydration