Agriculture Reference
In-Depth Information
as transcription factors. Seven of these predicted miR-
NAs (vun-miR156a, vun-miR159b, vun-miR160a,
vun-miR162a, vun-miR168a, vun-miR169b and vun-
miR408) were experimentally validated in the root
tissues and found to be upregulated during salt stress as
revealed by qRT-PCR (Paul et al., 2011). Dong et al.
(2013) studied the dynamic regulation of miRNA in
functioning soybean mature nodules under salt stress.
The authors identified 110 known miRNAs belonging to
61 miRNA families, and 128 novel miRNAs belonging to
64 miRNA families. Among them, 104 miRNAs were
dramatically differentially expressed (>2-fold or
detected only in one library) during salt stress. The
miR159bc, miR169c and miR319a,b were highly down-
regulated and gly_1, gly_3, miR171p and miR4416d
were highly upregulated by salt (Dong et al., 2013;
Mantri et al., 2013). Recently, Nageshbabu and Jyothi
(2013) analysed the expression of nine different miR-
NAs in Phaseolus vulgaris seedlings in response to 0.4 M
NaCl and drought stress. They reported that miR395
was most sensitive to both stresses and was upregulated
under both the stressors. Further, miR396 and miR172
were upregulated after exposure to both the stresses
(Mantri et al., 2013; Nageshbabu & Jyothi, 2013).
Wang and Long (2010) by using RT-PCR showed
miRNAs associated with cold tolerance in pea ( Pisum
sativum ), and the level of their expressions increased
after the cold treatment.
MicroRNAs are important signalling and regulatory
factors in P deficiency stress (Mantri et al., 2013). Under P
starvation stress, miR399 was induced in common bean
and M. truncatula (Valdes-Lopez & Hernandez, 2008).
This miRNA plays a key role in maintaining Pi (inorganic
phosphate) homeostasis in Arabidopsis and is induced
under P deficiency causing repression of the ubiquitin
conjugating enzyme UBC24, a repressor of phosphate
transporters (Chiou et al., 2006; Mantri et al., 2013).
Zeng et al. (2010) identified 57 miRNAs under P
deficiency in soybean. Also Sha et al. (2012), by using
deep sequencing of soybean root and shoot libraries con-
structed under P stress, identified 60 known and
conserved responsive miRNAs, belonging to 35 families.
Also, 16 novel predicted miRNAs were identified. In a
larger study, 167 miRNAs, belonging to 35 families, were
identified via differential expression in response to P
deficiency in white lupin; 17, 9 and 10 were found to be
upregulated, while 7, 6 and 12 were downregulated in
roots, stems and leaves, respectively (Zhu et al., 2010).
Recently, Xu et al. (2013) showed that 25 miRNAs were
induced and 11 mRNAs were repressed under P defi-
ciency in soybean.
Sulphur deficiency induced the suppression of
mRNA395 in legume species (Szittya et al., 2008;
Kawashima et al. 2009). This mRNA regulates ATP sul-
phurylase (APS4) and a sulphate transporter (AST68)
when maintaining S homeostasis during S deficiency
(Mantri et al., 2013).
Zeng et al. (2012) identified 30 stress-responsive miR-
NAs in Al-treated and non-treated roots. Of these, 10
were conserved miRNAs that belonged to seven fam-
ilies, 13 were unconserved and seven were novel. In
soybean, miR396, miR390 and miR1510a-p5 were
upregulated; miR156, miR164 and miR169 were down-
regulated; and miR1510a was non-responsive to Al
(Zeng et al., 2012). Chen et al. (2012) identified several
M. truncatula miRNA (miR160, miR319, miR396,
miR1507 miR1510a and miR390) as down-regulated
and other two (miR166 and miR171) not responsive to
Al treatment. Using a computational approach, Zhou et
al. (2008) identified 26 new miRNA candidates including
miR160, miR166, miR319, miR393 and miR398 that
were responsive to mercury, cadmium and aluminium
stresses. Their differential expressions were subse-
quently assessed in various M. truncatula organs and
tissues (Mantri et al., 2013).
1.7.2 Molecular marker-assisted breeding
Molecular markers are DNA regions tightly linked to
agronomic traits in crops, identified by using genetic
and genomic analysis. They can facilitate breeding strat-
egies for crop improvement. However, the use of
molecular markers in breeding programmes needs pre-
liminary studies to identify and validate potential
markers (Dita et al., 2006).
Several molecular marker-related techniques, such
as restriction fragment length polymorphism (RFLP),
amplified fragment length polymorphism (AFLP), ran-
domly amplified polymorphic DNA (RAPD), simple
sequence repeats (SSR) and derivatives, have been
reported for abiotic stresses (Kassem et al., 2004; Lee
et al., 2004). This has enhanced knowledge of the ge-
netic control of specific resistance and/or tolerance in
many legumes by giving information on the number,
chromosomal location and individual or interactive
effects of the different quantitative trait loci (QTLs)
involved (Dita et al., 2006).
Search WWH ::




Custom Search