factors (TFs), an MYB TF, and a phosphatase were identified that affect P uptake
Yamamoto et al. (2012). Several QTLs have also been identified in A. thaliana
which possibly harbor candidate genes for enhancing PU (El-Soda et al. 2019).
Multiple QTLs like KUP2, ATK2, KAT2, and TPK3 for potassium use efficiency
(KUE) in B. oleracea have been identified (White et al. 2010). QTLs have been
identified for NitUE in Arabidopsis (Loudet et al. 2003), barley (Kindu et al. 2014),
and rice (Wei et al. 2012); and QTLs for phosphate-stress in B. napus (Wang et al.
2020).
5.6.2 Nutrient Uptake Genes
One of the most direct ways of enhancing NUE is through manipulation of nutrient
uptake genes. In A. thaliana, overexpression of potassium high affinity transporter,
HAK5, enhances the tolerance to K-deficiency (Hong et al. 2013). Similarly sulfate
transporter SULTR1;2, SULTR2;1, SULTR4;1, SULTR4;2 which are induced upon
sulfate deficiency can be candidate genes for altering SUE (Yoshimoto et al. 2003;
Howarth et al. 2003; Zuber et al. 2010). OsNRT1.1B under the constitutive regulation of 35SCaMV promoter (Hu et al. 2015), OsNRT2.1 under control of OsNAR2.1
promoter (Chen et al. 2016), and OsNPF8.20 overexpressing lines have been shown
to increase NitUE where significant increase in yield was achieved (Fang et al. 2013;
Wang et al. 2018). Overexpression of OsNRT2.3b not only increased nitrate uptake,
but NH
4+ , P, and Fe uptake were also enhanced (Fan et al. 2016). In Pisum sativum,
overexpression of AMINOACIDPERMEASE1 (AAP1) causes improved N uptake
and utilization efficiency (Perchlik and Tegeder 2017).
5.6.3 Nutrient Assimilation Genes
N-assimilation genes such as GS1 have been used for increased NUE in tobacco,
maize, rice, and Arabidopsis (Eckes et al. 1989; Migge et al. 2000; Man et al. 2011).
Deciphering the functions and mechanisms of symbiotic bacteria and other root
microbiota for nitrogen fixation will also be helpful in achieving the purpose. AlaAT
overexpressing lines of Arabidopsis and O. sativa show enhanced biomass and seed
yield under low nitrogen conditions (Good et al. 2007; Shrawat et al. 2008).
GS/GOGAT genes have also proved to be a viable candidate for enhancing NiUE
(Lu et al. 2011). Recent studies have also identified role of nitrate transporters
NPF4.5 from O. sativa, Z. mays, and S. bicolor in root nodulation (Wang et al.
2020b), and NPF7.6 in root nodule symbiosis in Medicago truncatula (Wang et al.
2020a), and may hold potential for increased NitUE.
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 165
Yamamoto et al. (2012). Several QTLs have also been identified in A. thaliana
which possibly harbor candidate genes for enhancing PU (El-Soda et al. 2019).
Multiple QTLs like KUP2, ATK2, KAT2, and TPK3 for potassium use efficiency
(KUE) in B. oleracea have been identified (White et al. 2010). QTLs have been
identified for NitUE in Arabidopsis (Loudet et al. 2003), barley (Kindu et al. 2014),
and rice (Wei et al. 2012); and QTLs for phosphate-stress in B. napus (Wang et al.
2020).
5.6.2 Nutrient Uptake Genes
One of the most direct ways of enhancing NUE is through manipulation of nutrient
uptake genes. In A. thaliana, overexpression of potassium high affinity transporter,
HAK5, enhances the tolerance to K-deficiency (Hong et al. 2013). Similarly sulfate
transporter SULTR1;2, SULTR2;1, SULTR4;1, SULTR4;2 which are induced upon
sulfate deficiency can be candidate genes for altering SUE (Yoshimoto et al. 2003;
Howarth et al. 2003; Zuber et al. 2010). OsNRT1.1B under the constitutive regulation of 35SCaMV promoter (Hu et al. 2015), OsNRT2.1 under control of OsNAR2.1
promoter (Chen et al. 2016), and OsNPF8.20 overexpressing lines have been shown
to increase NitUE where significant increase in yield was achieved (Fang et al. 2013;
Wang et al. 2018). Overexpression of OsNRT2.3b not only increased nitrate uptake,
but NH
4+ , P, and Fe uptake were also enhanced (Fan et al. 2016). In Pisum sativum,
overexpression of AMINOACIDPERMEASE1 (AAP1) causes improved N uptake
and utilization efficiency (Perchlik and Tegeder 2017).
5.6.3 Nutrient Assimilation Genes
N-assimilation genes such as GS1 have been used for increased NUE in tobacco,
maize, rice, and Arabidopsis (Eckes et al. 1989; Migge et al. 2000; Man et al. 2011).
Deciphering the functions and mechanisms of symbiotic bacteria and other root
microbiota for nitrogen fixation will also be helpful in achieving the purpose. AlaAT
overexpressing lines of Arabidopsis and O. sativa show enhanced biomass and seed
yield under low nitrogen conditions (Good et al. 2007; Shrawat et al. 2008).
GS/GOGAT genes have also proved to be a viable candidate for enhancing NiUE
(Lu et al. 2011). Recent studies have also identified role of nitrate transporters
NPF4.5 from O. sativa, Z. mays, and S. bicolor in root nodulation (Wang et al.
2020b), and NPF7.6 in root nodule symbiosis in Medicago truncatula (Wang et al.
2020a), and may hold potential for increased NitUE.
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 165