Agrobacterium rhizogenes-Mediated Transformation and Its Biotechnological Applications in Crops - Crop Improvement: New Approaches and Modern Techniques - page 23

A . rhizogenes and Crop Biotechnology
Genes can be transferred between species and in conjunction with this fact; plant
improvements for many decades have been relied heavily upon gene transfer. Either
by natural selection or through the efforts of plant breeders, development of plants
has always depended upon creating, evaluating and selecting of right combination
of alleles. Transgenic plants possessing useful features such as resistance to dis-
eases, insects and pests have been developed by transferring such traits to crop
varieties from different species.
Since 1970, rapid progress being made in developing tools for recombinant DNA
technology has led to the creation of genetically modified plants. Genetically modi-
fied crops have been developed for improving various agricultural, nutritional and
food processing traits and used commercially all over the world (Miflin 2000 ; Kui-
per et al. 2001 ; James 2006 ; Olempska-Beer et al. 2006 ). Establishment of plant
tissue culture techniques are the most important and preliminary steps for many
direct (electroporation, biolistic, microinjection, etc.) and indirect (virus- or bacte-
ria-mediated) gene transfer methods in biotechnology and these methods are used
successfully by a lot of laboratories around the world (Ozyigit 2012 ). The particle
bombardment and electroporation transformation methods were favored DNA de-
livery systems because they do not show any plant host range problems and very
effective with high DNA delivery rate (Hauptmann et al. 1987 ; Birch 1997 ; Taylor
and Fauquet 2002 ; Turgut-Kara and Ari 2010 ). However with these methods, gene
silencing/co-suppression can be occurred as a result of high copy number of DNA
inserted in host cells (Block 1993 ; Yasuda et al. 2005 ). On the other hand, Agro-
bacterium -based plant transformation is very effective method of creating plants at
low cost, simple to use and with low copy number inserted. Limited number of host
range is the only disadvantage (Lessard et al. 2002 ; Chandra 2012 ). For achieving
transformation of plants, Agrobacterium based technology has been used since the
mid-1990s increasingly (Hiei et al. 1994 ). Agrobacterium -mediated transformation
in generating transgenic plants has been employed as a major DNA delivery system
for novel transgenic technologies starting with the transformations of dicotyledon-
ous (Zambryski et al. 1983 ) and monocotyledonous (Hiei et al. 1994 ) species in the
1980-1990s. Increasing understanding of Agrobacterium -plant relationship (Gelvin
2003 ) and the mechanisms of transgene integration and genetic recombination in
plants (Vain 2007 ) will lead to achieve further advances in these areas. Conducting
efficient and controlled research on targeted gene replacement/alteration, overex-
pression and mis-expression could provide valuable resource to define gene regula-
tion/function and traits in further in crops. Achievements on Agrobacterium -based
transformation technologies enable large-scale transgenic studies in a range of im-
portant plant and crop species (such as indica rice, wheat, barley, etc.) (Vain 2007 )
and also bring opportunity to define and select plant cultivars, which could not be
obtained by conventional breeding methods (Christou 1997 ).
For many crops, aim of breeding program is altering plant forms. Establishment
of plants with reduced size is favorable in many crops ranging from fruit trees to