Agriculture Reference
In-Depth Information
physiological processes in plants (Sunkar
et al.,
2007).
There is also a growing body of evidence showing that
miRNAs are involved in abiotic stresses. These include
drought (Trindade
et al.,
2010; T. Wang
et al.,
2011),
salinity (Ding
et al.,
2009; Liu
et al.,
2008), cold (Jin
et al.,
2010), nutrient deficiency (Bari
et al.,
2006; Pant
et al.,
2008; Liang
et al.,
2010), heavy metal stress (Zhou
et al.,
2008) and oxidative stress (Sunkar & Jagadeswaran,
2008). In legumes, miRNA research is still in its infancy
but has significantly progressed in the past few years,
resulting in the accumulation of both conserved and spe-
cies-specific miRNAs. In soybean, at least 129 miRNAs
have been identified (Subramanian
et al.,
2008; Wang
et
al.,
2009; Joshi
et al.,
2010; Turner
et al.,
2012). Similarly,
more than 100 miRNAs were identified in the model
legume
M. truncatula
(Szittya
et al.,
2008; Jagadeeswaran
et al.,
2009; Lelandais-Briere
et al.,
2009). In addition,
based on computational prediction and sequencing
approaches, a plethora of miRNA families, including
miRNA precursors and mature miRNAs, have been
reported in different legume species under abiotic stresses
(Valdes-Lopez
et al.,
2008; Barrera-Figueroa
et al.,
2011;
Chen
et al.,
2012a; Dong
et al.,
2013; Xu
et al.,
2013).
been established primarily through overexpression or by
generating plants that express miRNA-resistant versions
(Chen
et al.,
2004; Park
et al.,
2005; Schwab
et al.,
2005;
Gandikota
et al.,
2007; Li
et al.,
2010; Khan
et al.,
2011;
Bustos-Sanmamed
et al.,
2013; Turner
et al.,
2013).
Numerous studies have revealed that plant miRNAs
are involved in almost all biological and metabolic
processes (Comai & Zhang, 2012; Khraiwesh
et al.,
2012;
Sun 2012; Turner
et al.,
2013) including seed germina-
tion (Reyes & Chua, 2007), flower development and sex
determination (Chen, 2004; Chuck
et al.,
2009), plant
growth and development (Chen
et al.,
2004; Chen, 2005;
Willmann & Poethig, 2005; Jones-Rhoades
et al.,
2006;
Mallory & Vaucheret, 2006; Nogueira
et al.,
2006; Yang &
Xue, 2007; Lelandais-Briere
et al.,
2010; Rubio-Somoza &
Weigel, 2011), root development (Zhang
et al.,
2005;
Gutierrez
et al.,
2009) and phytohormone signalling
(Achard
et al.,
2004; Guo
et al.,
2005; Reyes & Chua,
2007; Meng
et al.,
2009). In addition, miRNA involve-
ment in biotic and abiotic stresses has been extensively
investigated and reported in plants (Sunkar & Zhu,
2004; Bari
et al.,
2006; Sunkar
et al.,
2006; Liu
et al.,
2008; Pant
et al.,
2008; Zhou
et al.,
2008; Ding
et al.,
2009;
Trindade
et al.,
2010, 2010; Liang
et al.,
2010; Wang
et al.,
2011). Given the fact that miRNAs are master regulators
and serve as the core of gene regulatory networks
(Jones-Rhoades
et al.,
2006), miRNA research provides
great opportunities to unravel the mechanisms under-
lying challenging plant traits (Sun, 2012; Liang
et al.,
2013). This chapter mainly focuses on the plethora of
miRNAs and their functions in legumes.
14.2 MicrorNas (mirNas):
Small but significant
Currently, miRNAs have been reported in 64 plant
species, and the miRNA database shows 24,521 mature
miRNA sequences (Release 20.0, June 2013;
http://
mirbase.org/
), including 6843 miRNAs from plant species.
However, the rate of miRNA identification in crop plants
has increased rapidly with the availability of complete
genome sequences due to high-throughput sequencing
methods, and improved computational and experimental
protocols (Yao
et al.,
2007; Subramanian
et al.,
2008;
Jagadeeswaran
et al.,
2009; Lelandais-Briere
et al.,
2009;
Joshi
et al.,
2010; Zhao
et al.,
2010; Schreiber
et al.,
, 2011;
Kim
et al.,
2012; Li
et al.,
2012; Wang
et al.,
2012; Zhang
et al.,
2012; Liang
et al.,
2013; Lin & Lai, 2013).
Interestingly in
Arabidopsis
, over 184 miRNAs have
been identified, which are predicted to regulate more than
600 genes including 225 known targets (Griffiths-Jones
et al.,
2008; Alves
et al.,
2009). Some of these miRNAs
have been analysed at the molecular level for their roles in
the regulation of target genes (Llave
et al.,
2002; Reinhart
et al.,
2002; Chen
et al.,
2004; Laufs
et al.,
2004; Duan
et al.,
2006). The regulatory roles of miRNAs in plants have
14.3 Micro-rNa identification and
functional diversity in legumes
Regulation of gene expression for proper functioning
is crucial for all organisms. Plant miRNAs function as
mediators to guide Argonaute (AGO) proteins in the
RNA-induced silencing complex (RISC) to cleave
target transcripts and/or repress translation (Bustos-
Sanmamed
et al.,
2013). Last decade has seen extensive
research into miRNA functions in plant development
and plant responses to abiotic and biotic stresses
(Khraiwesh
et al.,
2012). In plants, miRNAs can be
identified by high-throughput sequencing like miRNA
library sequencing (Ramesh
et al.,
2013) and computer
prediction (Xie
et al.,
2010). So far, hundreds of miRNAs
have been identified in many plant species, including
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