8.3
miRNA-TFs: Regulating Drought and Salinity
Drought and salinity are two major constraints to agricultural productivity worldwide. Over the past two decades the molecular basis of plant tolerance to these
stresses has identified numerous drought and salt stress responsive genes (Bartels
and Sunkar 2005). In addition to the protein coding genes, stress conditions also alter
miRNAs expression in plants (Fig. 8.1 and Table 8.1) (Sunkar and Zhu 2004; Zhao
et al. 2007; Li et al. 2008; Trindade et al. 2010; Kulcheski et al. 2011). In response to
drought stress, plants modify their root structure architecture (RSA) by inhibiting
primary root growth and increasing lateral root formation for maximum water
assimilation (Gilbert and Medina 2016). Accumulation of bioactive auxin indole3-acetic acid (IAA) is a known morphogenic trigger for lateral root formation and
contributes to the plastic changes in RSA (Benková et al. 2009). In Arabidopsis,
drought-mediated downregulation of miR167a that targets the TF HD-ZIP
(Homeodomain-leucine zipper) leads to accumulation of IAA-Ala RESISTANT
3 that promotes IAA accumulation and development of lateral roots (Kinoshita
et al. 2012). The miR165/166:HD-ZIP III module is negatively regulated by drought
and confers enhanced drought tolerance in Arabidopsis and rice, by elevated abscisic
acid (ABA) levels via enhanced HD-ZIP III activity (Yan et al. 2016; Zhang et al.
2018). Furthermore, miR164:NAC module also plays an important role in regulating
drought tolerance in rice, where overexpression of miR164 and concomitant depression of target NAC TFs leads to susceptibility to drought stress (Fang et al. 2014). In
another study by Jiang et al. (2019) it is shown that rice plants overexpressing the
miR164b-resistant form of OsNAC2 have higher levels of drought and salt tolerance
than the wild-type plants, and that the ABA content is increased in the transgenic
plants. In Arabidopsis, drought-mediated downregulation of miR169 allows the
induction of NF-YA5. Overexpression of NF-YA5 TF enhances drought tolerance,
while nf-ya5 mutant and miR169 overexpressing plants are hypersensitive to
drought (Li et al. 2008). In soybean, the miR169:GmNF-YA3 module also confers
drought tolerance, establishing conserved regulatory roles for miR169:NF-YA
modules in plant drought tolerance (Ni et al. 2013). In addition, plants have evolved
another mechanism to ensure the induction of NF-YA5 upon drought. In
Arabidopsis, an NF-YA5 cis-natural antisense gene called NERF (NF-YA5
ENHANCING RING FINGER) can produce short interfering RNAs (siRNAs) having sequence similar to miR169 that cannot direct the cleavage of NF-YA5
transcripts. Both miRNA and siRNA compete for the NF-YA5 binding preventing
miR169-mediated repression of NF-YA5 expression resulting in high accumulation
of NF-YA5 and enhanced drought tolerance in NERF overexpression lines (Gao et al.
2015b). Du et al. (2017) have demonstrated that miR169i and miR169l positively
regulate NF-YA5 expression via translational activation in response to dehydration
shock in Arabidopsis. Another report in soybean suggests that gma-miR169c negatively regulates the drought stress response by inhibiting the expression of the targets
AtNF-YA1 and AtNF-YA5 and reducing the transcript levels of the stress response
genes AtRD29A, AtRD22, AtGSTU25, and AtCOR15A (Yu et al. 2019). Feyissa et al.
(2019) have shown that low to moderate levels of miR156 expression are adequate to
8 Orchestration of MicroRNAs and Transcription Factors in the Regulation of Plant. . .
259
miRNA-TFs: Regulating Drought and Salinity
Drought and salinity are two major constraints to agricultural productivity worldwide. Over the past two decades the molecular basis of plant tolerance to these
stresses has identified numerous drought and salt stress responsive genes (Bartels
and Sunkar 2005). In addition to the protein coding genes, stress conditions also alter
miRNAs expression in plants (Fig. 8.1 and Table 8.1) (Sunkar and Zhu 2004; Zhao
et al. 2007; Li et al. 2008; Trindade et al. 2010; Kulcheski et al. 2011). In response to
drought stress, plants modify their root structure architecture (RSA) by inhibiting
primary root growth and increasing lateral root formation for maximum water
assimilation (Gilbert and Medina 2016). Accumulation of bioactive auxin indole3-acetic acid (IAA) is a known morphogenic trigger for lateral root formation and
contributes to the plastic changes in RSA (Benková et al. 2009). In Arabidopsis,
drought-mediated downregulation of miR167a that targets the TF HD-ZIP
(Homeodomain-leucine zipper) leads to accumulation of IAA-Ala RESISTANT
3 that promotes IAA accumulation and development of lateral roots (Kinoshita
et al. 2012). The miR165/166:HD-ZIP III module is negatively regulated by drought
and confers enhanced drought tolerance in Arabidopsis and rice, by elevated abscisic
acid (ABA) levels via enhanced HD-ZIP III activity (Yan et al. 2016; Zhang et al.
2018). Furthermore, miR164:NAC module also plays an important role in regulating
drought tolerance in rice, where overexpression of miR164 and concomitant depression of target NAC TFs leads to susceptibility to drought stress (Fang et al. 2014). In
another study by Jiang et al. (2019) it is shown that rice plants overexpressing the
miR164b-resistant form of OsNAC2 have higher levels of drought and salt tolerance
than the wild-type plants, and that the ABA content is increased in the transgenic
plants. In Arabidopsis, drought-mediated downregulation of miR169 allows the
induction of NF-YA5. Overexpression of NF-YA5 TF enhances drought tolerance,
while nf-ya5 mutant and miR169 overexpressing plants are hypersensitive to
drought (Li et al. 2008). In soybean, the miR169:GmNF-YA3 module also confers
drought tolerance, establishing conserved regulatory roles for miR169:NF-YA
modules in plant drought tolerance (Ni et al. 2013). In addition, plants have evolved
another mechanism to ensure the induction of NF-YA5 upon drought. In
Arabidopsis, an NF-YA5 cis-natural antisense gene called NERF (NF-YA5
ENHANCING RING FINGER) can produce short interfering RNAs (siRNAs) having sequence similar to miR169 that cannot direct the cleavage of NF-YA5
transcripts. Both miRNA and siRNA compete for the NF-YA5 binding preventing
miR169-mediated repression of NF-YA5 expression resulting in high accumulation
of NF-YA5 and enhanced drought tolerance in NERF overexpression lines (Gao et al.
2015b). Du et al. (2017) have demonstrated that miR169i and miR169l positively
regulate NF-YA5 expression via translational activation in response to dehydration
shock in Arabidopsis. Another report in soybean suggests that gma-miR169c negatively regulates the drought stress response by inhibiting the expression of the targets
AtNF-YA1 and AtNF-YA5 and reducing the transcript levels of the stress response
genes AtRD29A, AtRD22, AtGSTU25, and AtCOR15A (Yu et al. 2019). Feyissa et al.
(2019) have shown that low to moderate levels of miR156 expression are adequate to
8 Orchestration of MicroRNAs and Transcription Factors in the Regulation of Plant. . .
259