- How do the DNA integration patterns differ in plant cells, transformed via
Agrobacteriumand particle bombardment? - Can you think of additional methods for DNA introduction into plant cells?
10.1 Overview
Transgenic plantscan be simply defined as plants that contain additional or modified genes
that were introduced using specific physical or biological methods. The introduced DNAs
or transgenes are typically very well defined and are precisely manipulated in the laboratory
prior to delivery into the target plant cells. The methods for DNA introduction into
plants cells are quite varied and are dependent largely on the plant selected for study and
the background of the scientist performing the work. Over the years, tremendous efforts
have been placed in development of gene introduction or “transformation” technology
and, for many, if not most plants, the procedures have become almost routine. The effi-
ciency of transgenic plant production is still being improved, and new methods for DNA
delivery are still needed.
Although numerous methods have been developed for production of transgenic plants,
Agrobacteriumandparticle bombardmentare the two main methods used by most trans-
formation laboratories.Agrobacteriumhas been called a “natural genetic engineer” and
relies on thisbiologicalvector for transgene introduction. Particle bombardment is aphys-
icalmethod for DNA delivery and utilizes DNA-coated microscopic metal particles that are
accelerated toward a suitable target tissue. Although emphasis in most laboratories has been
placed on use ofAgrobacterium, most of the acreage of transgenic crops represents the
success of particle bombardment. Other procedures for DNA delivery do exist, and each
has benefits and drawbacks. In order to better understand the challenges of producing trans-
genic plants and the overall process, one must first try to visualize DNA delivery to a single
target plant cell and have a basic understanding of how to eventually recover a whole
genetically engineered plant from that single targeted cell.
10.2 Basic Components for Successful Gene Transfer to Plant Cells
10.2.1 Visualizing the General Transformation Process
Prior to the successful production of transgenic plants in the mid-1980s (Horsch et al.
1985), efforts to improve plants relied extensively on classical plant breeding through
sexual hybridization and evaluation of spontaneous or induced mutations. Although
plant breeding remains the foundation of plant improvement, a typical sexual cross
results in the mixing of tens of thousands of genes and requires sorting through progeny
to find the individuals with traits of interest. Through transgenic plant production, a
single gene of interest can be introduced into a plant, improving a previously productive
plant by a single, preselected gene or trait of interest. The basic concept is extremely
simple; introduce a single gene into a single cell and generate a whole plant from that
cell that will express the well-defined trait. The plant should beexactlythe same as the start-
ing material with the exception of the introduced transgene, which should impart a precise
new and improved characteristic to the plant. So, how do you get a gene into the plant cell
246 TRANSGENIC PLANT PRODUCTION