uptake, transfer, and partitioning have also been shown to be positively regulated via
arbuscular mycorrhizal associations of Glomus intraradices in roots of Daucus
carota (Allen and Shachar-Hill 2009).
Apart from the transporters associated with N, P, K, and S discussed in the
previous sections, there are others that are involved in uptake, transport, and
assimilation of other mineral nutrients and a representative list of key transporters
and molecular regulators are provided in Tables 5.4 and 5.5.
5.4
MicroRNAs in Nutrient Uptake and Stress
Several reports of small RNA sequencing, and expression analysis of candidate
genes has led to the identification of miRNAs involved in nutrient uptake and stress
in various plant species. Prominent miRNAs that have been shown to have altered
transcript levels under N-stress include miR156, miR169, miR172, miR319,
miR395, miR396, miR398, miR399, and others (Pant et al. 2009; Zhao et al.
2011; Liang et al. 2012; Ren et al. 2015; Zuluaga et al. 2017; Zuluaga and Sonnante
2019). In an earlier study, MIR169 family was shown to target NFγA family of TFs
which in turn are known to involve in drought resistance (Wang et al. 2003).
MIR169 was also found to be significantly downregulated under N deprived
conditions in A. thaliana (Zhao et al. 2011). Similar results were also observed in
Z. mays (Yang et al. 2019). Recently TaMIR444a was found to be upregulated under
N deficiency, and was found to regulate expression of several other nitrogen
responsive genes in wheat (Gao et al. 2016).
Several other miRNAs including miR896 and miR1222 that are upregulated
under P stress and, miR1211 that is downregulated in Lupinus under P stress;
microRNAs miR1122, miR1125, miR1135, miR1136 that are upregulated in Pdeficiency stress in wheat represent unique miRNAs that are specific to a particular
nutrient deficiency stress in a single species (Paul et al. 2015). MIR399 is known to
be a key regulator and the levels of miR399 are significantly increased in several
monocots as well as dicots in response to phosphate starvation. The MIR399 gene
family is a well characterized family which is known to be conserved across
monocots and dicots. Mature product of MIR399 has been shown to target and
regulate PHO2/UBC24 (a member of ubiquitin conjugase enzyme family) through
post-transcriptional gene regulation (PTGS), which is known to play crucial role in
degradation of several phosphate transporters (Bari et al. 2006). The MIR395 gene
family is known to be involved in sulfate starvation response acting via sulfate
transporters (AtSULTR2;1) and ATP sulfurylase (AtAPS4, AtAPS1) (JonesRhoades and Bartel 2004; Kawashima et al. 2009; Liang et al. 2010). In a recent
study, several miRNAs including novel ones were identified that may be involved in
Fe-homeostasis (Paul et al. 2016). Transcript levels of already known microRNAs
including those of miR166, miR399, and miR408, and novel microRNAs—miR11,
miR26, miR30, and miR31 were found to be significantly altered in transgenic rice
over-expressing Soy-FER1 (encoding ferritin protein). The four novel miRNAs were
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 151
arbuscular mycorrhizal associations of Glomus intraradices in roots of Daucus
carota (Allen and Shachar-Hill 2009).
Apart from the transporters associated with N, P, K, and S discussed in the
previous sections, there are others that are involved in uptake, transport, and
assimilation of other mineral nutrients and a representative list of key transporters
and molecular regulators are provided in Tables 5.4 and 5.5.
5.4
MicroRNAs in Nutrient Uptake and Stress
Several reports of small RNA sequencing, and expression analysis of candidate
genes has led to the identification of miRNAs involved in nutrient uptake and stress
in various plant species. Prominent miRNAs that have been shown to have altered
transcript levels under N-stress include miR156, miR169, miR172, miR319,
miR395, miR396, miR398, miR399, and others (Pant et al. 2009; Zhao et al.
2011; Liang et al. 2012; Ren et al. 2015; Zuluaga et al. 2017; Zuluaga and Sonnante
2019). In an earlier study, MIR169 family was shown to target NFγA family of TFs
which in turn are known to involve in drought resistance (Wang et al. 2003).
MIR169 was also found to be significantly downregulated under N deprived
conditions in A. thaliana (Zhao et al. 2011). Similar results were also observed in
Z. mays (Yang et al. 2019). Recently TaMIR444a was found to be upregulated under
N deficiency, and was found to regulate expression of several other nitrogen
responsive genes in wheat (Gao et al. 2016).
Several other miRNAs including miR896 and miR1222 that are upregulated
under P stress and, miR1211 that is downregulated in Lupinus under P stress;
microRNAs miR1122, miR1125, miR1135, miR1136 that are upregulated in Pdeficiency stress in wheat represent unique miRNAs that are specific to a particular
nutrient deficiency stress in a single species (Paul et al. 2015). MIR399 is known to
be a key regulator and the levels of miR399 are significantly increased in several
monocots as well as dicots in response to phosphate starvation. The MIR399 gene
family is a well characterized family which is known to be conserved across
monocots and dicots. Mature product of MIR399 has been shown to target and
regulate PHO2/UBC24 (a member of ubiquitin conjugase enzyme family) through
post-transcriptional gene regulation (PTGS), which is known to play crucial role in
degradation of several phosphate transporters (Bari et al. 2006). The MIR395 gene
family is known to be involved in sulfate starvation response acting via sulfate
transporters (AtSULTR2;1) and ATP sulfurylase (AtAPS4, AtAPS1) (JonesRhoades and Bartel 2004; Kawashima et al. 2009; Liang et al. 2010). In a recent
study, several miRNAs including novel ones were identified that may be involved in
Fe-homeostasis (Paul et al. 2016). Transcript levels of already known microRNAs
including those of miR166, miR399, and miR408, and novel microRNAs—miR11,
miR26, miR30, and miR31 were found to be significantly altered in transgenic rice
over-expressing Soy-FER1 (encoding ferritin protein). The four novel miRNAs were
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 151