Omics approaches and abiotic stress tolerance in legumes - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 219

and also are involved in tolerance mechanism in the
drought-tolerant variety.
Varshney et al. (2009) undertook a study encompass-
ing transcriptomics with the objective of collating as
many salinity-responsive and drought-responsive ESTs
of chickpea as possible. Drought stress was induced by
various treatments including polyethylene glycol (PEG)
induction, slow drought stress in both greenhouse and
field conditions, and dehydration, whereas salt stress
was instigated by the use of 80 mM NaCl. This study
produced a total number of 20,162 ESTs, 4558 drought-
responsive unigenes, 2595 salinity-responsive unigenes
and 9569 chickpea unigenes. This was the first work to
generate such a large number of ESTs in chickpea.
The effects of salt stress on the transcriptional
responses involving transcription factor (TF) genes in
the roots of chickpea were investigated by Gruber et al.
(2009). Two complementary transcriptomic approaches,
massive quantitative real-time PCR (qRT-PCR) and
Mt16K + microarray analysis, were used to identify the
salt-regulated TF genes. The PCR technique revealed 46
such genes, whereas the Mt16K + microarray analysis
identified 824 salt-regulated genes, of which 84 were TF
sequences. These genes showed significant changes in
their expression level ( p < 0.001) in root apexes after
being exposed to salinity. Analysis of stress regulation
in the root apex compared with whole roots revealed
several TF genes with more than 30-fold differences in
expression, including certain members of the MYB,
AP2/EREBP and HD-ZIP TF families.

factors and ion transporters as well as redox enzymes
(Umezawa et al., 2002).
Abiotic stress can affect a legume in various ways. For
instance, the symbiotic relationship between a legume
and rhizobia, as well as nitrogen fixation in the root
nodules, can be greatly affected by salt stress. Dong et al.
(2013) studied the molecular mechanisms involved in
regulating tolerance to salinity of functional nodules in
order to achieve genetic improvement in soybean, espe-
cially in its nitrogen fixation efficiency. Deep sequencing
of microRNAs (miRNAs) was carried out to decipher
the miRNA expression profile in mature nodules of
soybean under salt-induced stress and those under
control conditions. In the study, 104 miRNAs were
found to be dramatically differentially expressed during
salt stress conditions. The role of eight of these miRNAs
in the salt stress response was confirmed by qRT-PCR
analysis as they were dynamically regulated in the
functional soybean nodules in response to the salt
stress. Hence the study showed that miRNAs hold great
potential as players in the response of soybean nodules
during salt stress.
In another study conducted by Komatsu et al. (2009),
transcriptomic techniques were used to analyse genes
induced by flooding stress. Germination of soybeans
was carried out for 2 days and flooding conditions were
sustained for 12 hours, following which the RNAs were
extracted from the hypocotyl and the root. The tran-
scriptomic technique, high-coverage gene expression
profiling analysis, yielded 29,388 peaks. Ninety-seven of
these peaks demonstrated more than a 25-fold change
after 12-hour flood stress. Genes involved in ethylene
biosynthesis, alcohol fermentation, cell wall loosening
and pathogen defence were significantly upregulated.
Also, the genes of acid phosphatase, haemoglobin and
Kunitz trypsin protease inhibitor were greatly altered.
This indicates that the early responses of soybean after
flooding stress are potentially important in ensuring cell
survival after direct damage by water.

13.3.2 soybean
Soybean is the most intensively studied grain legume
and over 1.3 million ESTs have been developed
from different cDNA libraries according to Legume
Information System data. This is more ESTs than any
other grain legume. The discovery of new simple
sequence repeat (SSR) and single nucleotide polymor-
phism (SNP) markers for soybeans becomes possible due
to this large number of EST and bacterial artificial
chromosome (BAC) sequences, which in turn facilitate
the development of genetic maps with high resolution.
Moreover, using a modification of the complementary
DNA-amplified fragment length polymorphism (cDNA-
AFLP) technique in soybean, 140 differentially expressed
fragments of cDNA were observed when comparing
iso-osmotic treated soybean and control soybean. Most
of these genes were involved encoding transcription

13.4 proteomics

Proteomics is a biotechnological approach that involves
studying the proteome of an organism, i.e. the complete
profile of the expressed proteins in a given cell, tissue,
organ or complete organism (Memon, 2012; Lee et al.,
2013). It can be associated with two kinds of studies, the