Omics approaches and abiotic stress tolerance in legumes - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 226

virus vector is used to introduce a fragment of plant
gene into plant cells; this can trigger the plant defence
mechanism, which in turn silences the plant gene and
the virus. More than 30 VIGS vectors have been discov-
ered and are being used to decipher the function of
genes in cellular pathways, functions and abiotic stresses
(Huang et al., 2012).

can be defined as the study of the growth performance
as well as the composition of plants. In order to improve
plant performance by plant breeding, two phenomics
techniques can be employed, namely forward and
reverse phenomics. Phenotyping tools are used in for-
ward phenomics in order to 'sieve' collections of various
germplasm to isolate valuable traits. Forward phenom-
ics involves taking all of the genomes of the available
varieties and passing them through a sieve, leaving
behind only the germplasm of interest. One of the
screens that could be used, especially for research on
legumes, is abiotic stress. This approach hastens the
pre-breeding phase of research. In contrast, the second
approach is reverse phenomics, in which the phenotype
is known and researchers investigate the mechanisms
and genes responsible for the trait of interest.
Phenomics can be seen as a detailed dissection of
the traits of a plant that hold potential value and
hence can help understanding of the mechanisms and
processes involved in stress responses and tolerance.
The physiological trait isolated can be reduced to the
underlying biophysical or biochemical process and even
to the gene level ultimately.
Abiotic stress tolerance is a crucial trait as far as yield
stability and potential are concerned. Many traits that
contribute to stress tolerance can be screened at the
seedling stage of legumes in a controlled environment.
Two such extremely important traits are salinity and
drought tolerance. Stomatal closure is one of the first
effects of saline conditions on a plant, which is partly due
to the osmotic effect of solutes on the root uptake of
water from the soil. This leads to a reduction in photo-
synthesis. Hence a surrogate measure can be utilized for
photosynthetic or stomatal responses under osmotic stress
(Munns, 2010), which can also be extended to legumes.
Phenotyping allows the imaging of traits of interest
in real time. One very potent technique is advanced
phenotyping using field-portable near-infrared spec-
troscopy (NIRS) (Casler & van Santen, 2012). This
enables direct selection of the plant breed based on its
desirable traits. For instance, Casler and van Santen
(2012) selected certain forage legumes based on their
improved fixation of atmospheric nitrogen using this
technique. The plants were screened on the basis of
high tissue N concentrations, which correlated with
enhanced fixation of atmospheric nitrogen. This shows
how phenotypic imaging can be used for plant screen-
ing and selection. The technique can be extended to
other legumes and also to other traits.

13.8.2 tilling
The basic principle of the functional genomics platform
revolves around the ability to study the function of a
gene or an entire cell, by introducing mutations or
altering growth conditions, and determining the result-
ing response of the organism. One reverse-genetics
technique for introducing mutations is the target-
induced local lesions in genome (TILLING) technique,
which utilizes traditional mutagenesis techniques to
create libraries of mutagenized individuals, which are
then subjected to screening for mutations and studied
for determining gene function. In order to study gene
function by this technique, TILLING populations have
been developed in numerous legumes. For example, in
case of peanut, candidate genes for allergenicity are
being identified using a TILLING population of 10,000
lines (Tadege et al., 2009). Similarly, the development of
approximately 3500 TILLING population lines is being
carried out for the identification of candidate genes for
drought tolerance in chickpea (Thudi, 2013a).
In a study carried out by Betti et al. (2012), the mutant
alleles of specific genes involved in the drought stress
response of L. japonicus were identified using a TILLING
reverse genetics tool along with a population of insertion
mutants created by the LORE1 endogenous transposon.
The gene that was induced most by drought conditions
was orthologous to the Oep16 gene of Arabidopsis . The
corresponding protein of this gene belongs to a family of
amino acid and pre-protein transporters that are respon-
sible for the transport of cytosol-synthesized proteins.
This study shows that the use of TILLING can provide
great insight into the responses of legumes under abi-
otic stress and can easily help identify the proteins
involved in stress-induced responses.

13.9 phenomics

Simply put, phenomics is the study of how the genetic
composition of an organism affects its appearance,
function and performance. Alternatively, phenomics