8.7
miRNAs-TFs: Regulating Nitrogen Homeostasis
Nitrogen (N) plays an essential role in growth and development of plants. It is a
major component of nucleic acids, amino acids, co-enzymes, and a myriad of plant
secondary metabolites. In soil, N is available in different forms, plants predominantly take up N in the form of nitrate and ammonium. The availability of N to plant
roots is often an important limitation for plant growth and crop yield (Richardson
et al. 2009; McAllister and Beatty 2012). To counter this, plants have developed
multiple strategies, including physiological, morphological, and biochemical
adaptations (Schachtman and Shin 2007; Kant et al. 2011; Kraiser et al. 2011).
Plants can adapt in N-limiting soil conditions by up- or downregulating a specific
group of nitrogen exporter or importer proteins. Several miRNAs regulating
transporters have been reported in the literature. In Arabidopsis, nitrogen responsive
miRNAs are classified into two groups, the first is named as N-starvation-induced
(NSI) miRNA families that include miR156, miR160, miR169, miR171, miR319,
miR826, miR829, miR839, and miR846, whereas miR167, miR172, miR399,
miR395, miR850, miR857, miR863, and miR827 are grouped into N-starvationsuppressed (NSS) miRNAs (Liang et al. 2012). Two members of the NSS group.
Viz. miR167 and miR393 regulate root growth in response to N (Gifford et al. 2008;
Vidal et al. 2010). Nitrate deficiency mediated regulation of miRNA expression is
reported in multiple plants (Pant et al. 2009; Jeong et al. 2011; Fischer et al. 2013;
Liu et al. 2020b; Hou et al. 2020; Vakilian 2020). About 15 and 14 miRNA families
have been identified to be responsive in N-limiting conditions in rice and maize,
respectively (Xu et al. 2011). In Arabidopsis, miR156 family has been found at the
highest abundance and miR156h is thought to be the most important among the three
members of the miR156 family under N-limited conditions (Liang et al. 2012).
N-starvation mediated induction of miR160 inhibits lateral root development,
whereas miR170 mediated cleavage of AUXIN RESPONSE FACTOR (ARF16/17)
TF and SCL6 regulatory protein transcripts hastens the primary root growth, respectively (Liang et al. 2012). In contrast, the perturbation of miR167 biogenesis in
N-limiting condition attenuates the expression of ARF6/8, which in turn facilitates
the development of lateral and adventitious roots (Jones-Rhoades and Bartel 2004;
Gifford et al. 2008). Furthermore, nitrate deficiency leads to downregulation of
miR169a and upregulation of its target NF-YA TF family members in Arabidopsis.
The miR169-NF-YA module likely regulates the adaptive response of nitrate uptake
systems as is evident by overexpression of miR169. Enhanced miR169 levels reduce
expression of multiple nitrate transporter genes and cause an early senescence
phenotype (Zhao et al. 2011). This regulatory role of miR169:NF-YA module in
response to nitrate starvation is also conserved in wheat where overexpression of
TaNF-YAB1 significantly enhances the uptake of both nitrate and phosphate and
leads to enhanced grain yield in a field experiment with different levels of nutrient
supply (Qu et al. 2015).
264
S. Rao et al.
miRNAs-TFs: Regulating Nitrogen Homeostasis
Nitrogen (N) plays an essential role in growth and development of plants. It is a
major component of nucleic acids, amino acids, co-enzymes, and a myriad of plant
secondary metabolites. In soil, N is available in different forms, plants predominantly take up N in the form of nitrate and ammonium. The availability of N to plant
roots is often an important limitation for plant growth and crop yield (Richardson
et al. 2009; McAllister and Beatty 2012). To counter this, plants have developed
multiple strategies, including physiological, morphological, and biochemical
adaptations (Schachtman and Shin 2007; Kant et al. 2011; Kraiser et al. 2011).
Plants can adapt in N-limiting soil conditions by up- or downregulating a specific
group of nitrogen exporter or importer proteins. Several miRNAs regulating
transporters have been reported in the literature. In Arabidopsis, nitrogen responsive
miRNAs are classified into two groups, the first is named as N-starvation-induced
(NSI) miRNA families that include miR156, miR160, miR169, miR171, miR319,
miR826, miR829, miR839, and miR846, whereas miR167, miR172, miR399,
miR395, miR850, miR857, miR863, and miR827 are grouped into N-starvationsuppressed (NSS) miRNAs (Liang et al. 2012). Two members of the NSS group.
Viz. miR167 and miR393 regulate root growth in response to N (Gifford et al. 2008;
Vidal et al. 2010). Nitrate deficiency mediated regulation of miRNA expression is
reported in multiple plants (Pant et al. 2009; Jeong et al. 2011; Fischer et al. 2013;
Liu et al. 2020b; Hou et al. 2020; Vakilian 2020). About 15 and 14 miRNA families
have been identified to be responsive in N-limiting conditions in rice and maize,
respectively (Xu et al. 2011). In Arabidopsis, miR156 family has been found at the
highest abundance and miR156h is thought to be the most important among the three
members of the miR156 family under N-limited conditions (Liang et al. 2012).
N-starvation mediated induction of miR160 inhibits lateral root development,
whereas miR170 mediated cleavage of AUXIN RESPONSE FACTOR (ARF16/17)
TF and SCL6 regulatory protein transcripts hastens the primary root growth, respectively (Liang et al. 2012). In contrast, the perturbation of miR167 biogenesis in
N-limiting condition attenuates the expression of ARF6/8, which in turn facilitates
the development of lateral and adventitious roots (Jones-Rhoades and Bartel 2004;
Gifford et al. 2008). Furthermore, nitrate deficiency leads to downregulation of
miR169a and upregulation of its target NF-YA TF family members in Arabidopsis.
The miR169-NF-YA module likely regulates the adaptive response of nitrate uptake
systems as is evident by overexpression of miR169. Enhanced miR169 levels reduce
expression of multiple nitrate transporter genes and cause an early senescence
phenotype (Zhao et al. 2011). This regulatory role of miR169:NF-YA module in
response to nitrate starvation is also conserved in wheat where overexpression of
TaNF-YAB1 significantly enhances the uptake of both nitrate and phosphate and
leads to enhanced grain yield in a field experiment with different levels of nutrient
supply (Qu et al. 2015).
264
S. Rao et al.