5.6.4 Regulatory Genes Including Transcription Factors
and miRNAs
Overexpression of PHR1 which is one of major TF led to upregulation of P-uptake
(Nilsson et al. 2007). Expression of several other TFs such as ZmDof1 (TF) in wheat
(Peña et al. 2017), OsRDD1—a Dof1 TF in rice (Iwamoto and Tagiri 2016), HY5—
a bZip TF in A. thaliana (Chen et al. 2016) has been demonstrated to play role in
Nitrogen uptake (Li et al. 2017b). The transcription factor TaNAC2-5A was shown
to regulate 106 genes, leading to increased NiUE in wheat (He et al. 2015). As has
been elaborated previously (Table 5.6), several miRNAs have been identified as key
regulators of nutrient uptake such as miR399 and miR395 for P and S, respectively.
As a demonstration, over-expression of MIR528 in rice increases tolerance to
N-starvation in Agrostis stolonifera (Yuan et al. 2015); and overexpression of
miR169o in rice led to increased NitUE (Yu et al. 2018). Several miRNAs that
exhibit altered expression pattern under nutrient-starvation are also involved in
shaping other key traits such as root system architecture (miR167; miR160),
flowering time (miR156; miR172; miR167), plant architecture along with nutrient
uptake and homeostasis (miR156) (de Lima et al. 2012; Liu et al. 2018; Song et al.
2019). It should, therefore, be borne in mind that key regulators such as miRNAs are
involved in developmental processes and any manipulation of NUE through
employing miRNAs genes is also likely to alter developmental processes (Fischer
et al. 2013).
5.6.5 Other Genes
Over-production of RUBISCO in transgenic rice led to improved NitUE under
sufficient N fertilization (Yoon et al. 2020). Members of Bric-a-Brac/Tramtrack/
Broad (BTB)/BT gene family encoding BT2 proteins have been shown to be negative
regulators of NitUE, and loss-of-function bt2/bt2 mutants exhibit significantly
higher levels of nitrate uptake in Arabidopsis (Araus et al. 2016). Arabidopsis and
rice transgenic lines overexpressing H
+ -PPase (AVP1D) are shown to have better
P and K uptake, biomass, and seed yield than control plants under limited
P conditions (Yang et al. 2007). Two isozymes of purple APase (PAP), AtPAP12
and AtPAP26, that are involved in phosphate scavenging have been proposed as
useful candidates that have the potential for improving PUE in A. thaliana
(Robinson et al. 2012). Increased activity of a phosphate-starvation inducible
gene, Fructose-1,6-bisphosphatase (FBPase), in root nodules of Phaseolus vulgaris
was found to be tightly linked and correlated to both increased rhizobial symbiosis
and enhanced PUE (Lazali et al. 2016). In another approach, polyploids have been
proposed to have higher KUE in Arabidopsis (Chao et al. 2013).
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E. Bhardwaj et al.
and miRNAs
Overexpression of PHR1 which is one of major TF led to upregulation of P-uptake
(Nilsson et al. 2007). Expression of several other TFs such as ZmDof1 (TF) in wheat
(Peña et al. 2017), OsRDD1—a Dof1 TF in rice (Iwamoto and Tagiri 2016), HY5—
a bZip TF in A. thaliana (Chen et al. 2016) has been demonstrated to play role in
Nitrogen uptake (Li et al. 2017b). The transcription factor TaNAC2-5A was shown
to regulate 106 genes, leading to increased NiUE in wheat (He et al. 2015). As has
been elaborated previously (Table 5.6), several miRNAs have been identified as key
regulators of nutrient uptake such as miR399 and miR395 for P and S, respectively.
As a demonstration, over-expression of MIR528 in rice increases tolerance to
N-starvation in Agrostis stolonifera (Yuan et al. 2015); and overexpression of
miR169o in rice led to increased NitUE (Yu et al. 2018). Several miRNAs that
exhibit altered expression pattern under nutrient-starvation are also involved in
shaping other key traits such as root system architecture (miR167; miR160),
flowering time (miR156; miR172; miR167), plant architecture along with nutrient
uptake and homeostasis (miR156) (de Lima et al. 2012; Liu et al. 2018; Song et al.
2019). It should, therefore, be borne in mind that key regulators such as miRNAs are
involved in developmental processes and any manipulation of NUE through
employing miRNAs genes is also likely to alter developmental processes (Fischer
et al. 2013).
5.6.5 Other Genes
Over-production of RUBISCO in transgenic rice led to improved NitUE under
sufficient N fertilization (Yoon et al. 2020). Members of Bric-a-Brac/Tramtrack/
Broad (BTB)/BT gene family encoding BT2 proteins have been shown to be negative
regulators of NitUE, and loss-of-function bt2/bt2 mutants exhibit significantly
higher levels of nitrate uptake in Arabidopsis (Araus et al. 2016). Arabidopsis and
rice transgenic lines overexpressing H
+ -PPase (AVP1D) are shown to have better
P and K uptake, biomass, and seed yield than control plants under limited
P conditions (Yang et al. 2007). Two isozymes of purple APase (PAP), AtPAP12
and AtPAP26, that are involved in phosphate scavenging have been proposed as
useful candidates that have the potential for improving PUE in A. thaliana
(Robinson et al. 2012). Increased activity of a phosphate-starvation inducible
gene, Fructose-1,6-bisphosphatase (FBPase), in root nodules of Phaseolus vulgaris
was found to be tightly linked and correlated to both increased rhizobial symbiosis
and enhanced PUE (Lazali et al. 2016). In another approach, polyploids have been
proposed to have higher KUE in Arabidopsis (Chao et al. 2013).
166
E. Bhardwaj et al.