Agriculture Reference
In-Depth Information
the regulation of transcription factors offers diverse
means to protect legumes from the stress factors.
Another category of abiotic stress response elements
comprises the genes encoding the machinery for synthe-
sizing various metabolic products, including amino acids,
amines, carbohydrates, sugar alcohols and various
secondary metabolites (Betti et al., 2012; El-Rahman
et al., 2012; Silvente et al., 2012; Palma et al., 2013; Wink,
2013). The gene products formed thereafter interact with
the target sites to produce their effects. Another impor-
tant class of chemicals that significantly affect the legume
response to any abiotic stress is the molecular chaper-
ones. Of these, heat-shock proteins (HSPs) serve as
members of the molecular cascade involved in protection
from not only heat stress but also water and salt stress at
relatively lower temperatures (Al-Whaibi, 2011).
Another class of proteins that assist the plant in tolerating
a freezing environment are the late embryogenesis abun-
dant (LEA)-type proteins. These molecules are involved
in providing cryoprotection to the plant (Thomashow,
1999). LEA-type proteins are hydrophilic in nature and
help the threatened cell by increasing membrane stability
at freezing temperatures. The HSPs commonly observed
in legumes include HspB1, Hsp60, Hsp70 and a variety of
other molecular chaperones (Hernandez & Vierling, 1993;
Brunet et al., 2009; Komatsu & Ahsan, 2009; Pick et  al.,
2012; Qu et al., 2013). The LEAs mainly expressed in
legumes are LEA1 (GmD19, GmPM11), LEA2 (GmPM6),
LEA3 (GmPM30) and LEA4 (GmPM1, GmPM9) 1 (Liu
et al., 2011; Battaglia & Covarrubias, 2013).
Apart from the natural responses observed in many
plants, introduction of stress-responsive foreign genes
or gene cassettes can also prove to be very beneficial.
Engineering of certain transcription factors like
C-repeat-dehydration response elements (CRT/DRE)
and CBF3 elements in legumes, like chickpea, Medicago
spp., soybean and peanut, help in the induction of cold-
regulated gene systems (Chen et al., 2010; Mantri et al.,
2012; Reddy et al., 2012). Consequently, a number of
genes are regulated to elicit a response by altering
metabolic and other phenotypic activities. Significant
among these changes are increased levels of proline,
sugars and enhanced tolerance to chilling temperatures.
Apart from the transcription factors, genes encoding the
production and regulation of certain metabolites are
also utilized for enhancing tolerance to both biotic and
abiotic stress. Proline, a potent stress-response agent, is
produced by glutamic acid metabolism (Szabados &
Savouré, 2010). The principal enzymes involved are
pyrroline-5-carboxylate (P5C) synthase (P5CS), P5C
reductase (P5CR), proline dehydrogenase (ProDH) and
P5C dehydrogenase (Lehmann et al., 2010). Transgenic
legumes like groundnut, chickpea and clovers express-
ing mutated forms of P5CS have been associated with
isolation of larger quantities of proline and, conse-
quently, better salt resistance (Bhatnagar-Mathur et al.,
2009; Magyar-Tábori et al., 2011; Vaseva et al., 2012).
Additionally, introduction of a trehalose overexpression
system into legumes, including Medicago spp. and many
forage varieties, likewise can help provide better osmo-
protection and drought tolerance (Alam et al., 2010).
An understanding of these response mechanisms can
help in devising strategies to target various molecular and
cellular mechanisms by molecular biology approaches.
The genes identified can help in providing the targets for
molecular intervention to control and respond to various
stress factors, biotic and abiotic, in an effective way.
15.6 Biotechnology in legumes
Biological and physical stress conditions are responsible
for significant losses in legumes. Traditional methods of
control include the use of fungicides, pesticides and
other hazardous chemicals for treating various biotic
constraints. However, in case of any physical stress, the
farmer has to bear huge financial losses due to reduced
quality and agricultural yield. Molecular intervention
techniques for combating stress conditions have helped
in improving the yield and quality of legumes in a
safer fashion. Biotechnology identifies and manipulates
the potential checkpoints that can be beneficial for
defence against any biotic or abiotic constraint. Moreover,
the overall output of the legumes has improved, aiding
the achievement of better financial returns.
15.6.1 applications
The use of biotechnology approaches for protect-
ing  legumes from any physical or biological threat
involves  expertise from various fields of study. From
1 Each LEA protein class consists of various proteins. Here, Gm refers to  Glycine max (soybean) followed by the protein name according to
nomenclatural convention.
 
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