Agriculture Reference
In-Depth Information
constitutive promoter (Douches
et al
., 2011),
have all been demonstrated to diminish damage
by potato tuberworm (
Phthorimaea opercullela
).
The
Amaranthus caudatus
agglutinin (
ACA
) gene
has been demonstrated to convey partial resist-
ance to aphid attack in transgenic potato in both
greenhouse and field trials (Yang
et al
., 2011a).
Suppression of root invasion by the potato cyst
nematode (
Globodera pallida
) was achieved in
transgenic potato by tissue-specific expression in
the root tips, using the Arabidopsis MDK4-
20
promoter to drive the expression of a di-
sulfide-constrained
7-
mer peptide (nAChRbp) to
inhibit chemoreception of the nematode pest
without affecting the incidence of non-invasive
nematodes (Green
et al
., 2012).
Miscellaneous other potato transgenics
have emerged in recent years, including the
introduction of a uridine diphosphate (UD-
P)-glucose lavoloid-
3-
O
-glucosyltransferase gene
(Wei
et al
., 2012) to enhance the tuber skin color
of Desiree, and overexpressing the sucrose syn-
thase (
SuSy
) gene in tubers to increase starch ac-
cumulation and yield (Baroja-Fernández
et al
.,
2009). A molecular farming approach was used
to harvest a viral protein gene (glycoprotein
(GP) 5) from the virus that causes porcine repro-
ductive and respiratory syndrome, in order to
develop an inexpensive vaccination for swine
(Chen and Liu, 2011). Increased tuber size and
greater tuber yield were reported for a Korean
potato cultivar overexpressing the Arabidopsis
jasmonic acid carboxyl methyltransfease gene
(Sohn
et al
., 2011). A reduction in enzymatic
browning of potato tubers was achieved by
transformation with a hairpin construct de-
signed to silence native polyphenol oxidase
(
PPO
) genes (Llorente
et al
., 2011). An unin-
tended consequence was that the transgenic,
non-browning potatoes maintained their aroma
in storage longer than the controls (Llorente
et al
., 2010).
The emergence of potato genomics has
opened many new possibilities for the improve-
ment of potato using transgenic approaches. An
obvious strategy is to identify potato orthologs of
genes identified in other organisms in order to
develop politically less objectionable cisgenic ra-
ther than transgenic approaches to potato trans-
formation. Overexpression of such orthologs
may result in similarly desirable traits in the cis-
genic plants, as would have been obtained in
transgenic lines using a heterologous gene. The
genome also offers the possibility of promoter
analysis to identify regulatory sequences in
order to target the expression of transgenes to
the specific tissue where they can be most effect-
ive, while reducing or eliminating the presence
of alien proteins in the edible tubers.
A recent breakthrough technology has been
described whereby whole pathways can be intro-
duced into a crop plant through multitransgenic
binary vector construction using zinc finger nucle-
ases and homing endonucleases (Zeevi
et al
.,
2012). The initial study described the insertion of
up to nine genes concurrently into Arabidopsis us-
ing a single vector. Likewise, targeted mutagenesis
through the regulated expression of zinc finger nu-
cleases offers new opportunities for determining
the function of previously unannotated genes
through homologous recombination by a knock-
out technique without the need for the develop-
ment of extensive mutant populations (Armstrong
et al
., 2005). Li
et al.
(2012) demonstrated the po-
tential of this TALEN (transcription activator-like
effector nuclease) technology by modifying a sus-
ceptibility gene of rice to
Xanthomonas oryzae
,
thereby conveying resistance to the pathogen. It is
important to note that the possibility of undesir-
able somaclonal variation is ever-present during
the application of any of these technologies, so
that it is always essential to regenerate many differ-
ent plants from unique events in order to select for
normal phenotypes (Barrell and Conner, 2011).
17.
7
Comparative Genomics
Comparative genomics is the study of the rela-
tionship of genome structure and function
across different biological species or strains
(Goodstein
et al
., 2012). Researchers use com-
parative genomics to understand the function
and evolutionary processes that act on genomes.
Similarities and differences in the proteins, RNA,
and regulatory regions of different organisms
are important components of comparative gen-
omics. Genome elements that are responsible for
similarities between different species should be
conserved through time, while elements respon-
sible for differences among species should be di-
vergent. Elements that are unimportant to the
evolutionary success of the organism will not be
