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new transgenics methodologies should be developed since the current methods are
laborious and time-consuming. In a recent study, drought enhancement of bread
wheat was established with the overexpression of barley HVA1, using a novel tech-
nique, which combines doubled haploid technology and Agrobacterium-mediated
genetic transformation (Chauhan and Khurana 2011 ). Most of the transformed genes
are from model plants such as Arabidopsis and rice or from wheat and barley cul-
tivars. These approaches could be applied to wild relatives whose genes may have
stronger effects. This hypothesis awaits experimental confirmation and field testing.
Plant miRNAs are approximately 20–24-nucleotide noncoding RNAs that spe-
cifically base pair to and induce the cleavage of target mRNAs or cause transla-
tional inhibition (Zhang et al. 2006b; Shukla et al. 2008 ). They have diverse roles
in plant development, such as phase transition, leaf morphogenesis, floral organ
identity, developmental timing, and other aspects of plant development (Lu and
Huang 2008 ; Rubio-Somoza and Weigel 2011 ). To date, numerous miRNAs from
diverse plant species have been identified and functionally characterized in plant
development as well as stress response to biotic and abiotic environmental factors
(Eldem et al. 2013 ). More than 40 miRNA families in plants have been associated
with response to abiotic stress such as salt and drought (Sunkar 2010 ; Covarrubias
and Reyes 2010 ). For instance, miR167, miR168, miR171, and miR396 were found
to be drought-responsive miRNAs in Arabidopsis (Liu et al. 2008 ). In search of
potential miRNAs involved in drought response in barley, some of the miRNAs,
such as miR156, miR171, miR166, and miR408, were observed as differentially
expressed upon dehydration (Kantar et al. 2011 ). miR166 is an example of many
drought-responsive miRNAs that were previously characterized as crucial for cell
development. It posttranscriptionally regulates class-III homeodomain-leucine zip-
per ( HD-Zip III) transcription factors, which were demonstrated to be important
for lateral root development, axillary meristem initiation, and leaf polarity (Hawker
and Bowman 2004 ; Boualem et al. 2008 ). It is likely that differential regulation
of miRNAs in different tissues is important for adaptation to stress in plants. For
example, four miRNAs displayed tissue-specific regulation during dehydration in
barley: miR166 was up-regulated in leaves, but down-regulated in roots; and mi-
R156a, miR171, and miR408 were induced in leaves, but unaltered in roots (Kantar
et al. 2011 ). Studying drought-responsive miRNAs and their target gene expression
in individual cell types will provide greater insights into miRNA target networks
that operate in a cell- or tissue-specific manner under drought stress. Zhou et al.
( 2013 ) reported that the overexpression of miR319 impacts plant development and
enhances plant drought and salt tolerance. The miR319-mediated down-regulation
of target genes in transgenic plants may have caused changes in various biologi-
cal processes, including those associated with water retention capacity, leaf wax
synthesis, and salt uptake beneficial to plants responding to salinity and water defi-
ciency. The manipulation of miR319 target genes provides novel molecular strate-
gies to genetically engineer crop species for enhanced resistance to environmental
stress. An increasing understanding of the role of miRNAs in drought and salinity
tolerance will enable the use of miRNA-mediated gene regulation to enhance plant
drought and salinity tolerance.