5.7
Modified Root System Architecture (RSA)
Changes in root morphology are primary adaptive features of plants for their survival
under various stresses that are linked to soil health including availability of mineral
nutrients and nutrient related stresses. Several genes and promoters have been
identified which are not directly involved in nutrient uptake or assimilation pathway,
but can modulate or alter root architecture and morphology which help plants in
coping up and adapting to nutrient stresses. Several transcription factors such as CPC
(Tominaga-Wada and Nukumizu 2012; Kirik et al. 2004), MYB77 (Shin et al.
2007), NAC1 (Xie et al. 2000), KNAT6 (Dean et al. 2004), and ANR1 (Montiel
et al. 2004; Zhang and Forde 1998) that are involved in altering root architecture by
initiating lateral roots under potassium stress have been identified. These TFs under
the control of root specific promoters can thus be helpful in enhancing KUE.
Similarly, several genes have been identified which are sensitive to low Pi and
play role in primary root elongation (SIZ1; Miura et al. 2005, PRD; CamachoCristóbal et al. 2008) and induce lateral roots and root hairs (PNP; Marchive 2009,
FBX; Chen et al. 2008b). Nitrogen stress is known to induce primary root growth,
with complex interactions with phytohormones such as auxin, cytokinin, ethylene,
abscisic acid (ABA), brassinosteroids (BRs), strigolactones (SLs), as well as nitric
oxide (NO). For example, auxin transporters such as ZmPIN1a can lead to higher
auxin concentration in roots (Li et al. 2018) and thus promote PR growth (similar to
adaptive strategy of plants mild N deficiency). Similarly, mutation in auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE RELATED 2 (TAR2) can
lead to impaired LR growth.
5.8
Conclusion, Future Prospects, and Scope
Excessive use of chemical fertilizers to supplement and provide mineral nutrition,
and irrigation in order to boost crop yield for ever-increasing demand has caused
serious damage to soil health, and altered ecosystem dynamics (Guignard et al.
2017). The founding principles of first green-revolution thus have serious environmental limitations and repercussions. Advancements in understanding molecular
basis of mineral nutrient uptake by plants, transport and assimilation into the
biological system, coupled with insights into plant development such as that of
root system architecture, and understanding physiological basis of nutrient uptake
have opened up newer vistas. Identification of transporter families, transcription
factors, and regulatory microRNAs involved in uptake and plant development,
coupled with genomic and breeding strategies such as reverse genetics or transgenic
technologies, genome editing, and marker-assisted breeding and selection has the
potential to significantly increase nutrient uptake, transport and assimilation
efficiencies in not only model plants but in crop species.
Acknowledgements The award of JRF/SRF from UGC and DBT to EB, and JRF from CSIR to
RS is gratefully acknowledged. Research in our laboratory is funded by Department of
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 167
Modified Root System Architecture (RSA)
Changes in root morphology are primary adaptive features of plants for their survival
under various stresses that are linked to soil health including availability of mineral
nutrients and nutrient related stresses. Several genes and promoters have been
identified which are not directly involved in nutrient uptake or assimilation pathway,
but can modulate or alter root architecture and morphology which help plants in
coping up and adapting to nutrient stresses. Several transcription factors such as CPC
(Tominaga-Wada and Nukumizu 2012; Kirik et al. 2004), MYB77 (Shin et al.
2007), NAC1 (Xie et al. 2000), KNAT6 (Dean et al. 2004), and ANR1 (Montiel
et al. 2004; Zhang and Forde 1998) that are involved in altering root architecture by
initiating lateral roots under potassium stress have been identified. These TFs under
the control of root specific promoters can thus be helpful in enhancing KUE.
Similarly, several genes have been identified which are sensitive to low Pi and
play role in primary root elongation (SIZ1; Miura et al. 2005, PRD; CamachoCristóbal et al. 2008) and induce lateral roots and root hairs (PNP; Marchive 2009,
FBX; Chen et al. 2008b). Nitrogen stress is known to induce primary root growth,
with complex interactions with phytohormones such as auxin, cytokinin, ethylene,
abscisic acid (ABA), brassinosteroids (BRs), strigolactones (SLs), as well as nitric
oxide (NO). For example, auxin transporters such as ZmPIN1a can lead to higher
auxin concentration in roots (Li et al. 2018) and thus promote PR growth (similar to
adaptive strategy of plants mild N deficiency). Similarly, mutation in auxin biosynthesis gene TRYPTOPHAN AMINOTRANSFERASE RELATED 2 (TAR2) can
lead to impaired LR growth.
5.8
Conclusion, Future Prospects, and Scope
Excessive use of chemical fertilizers to supplement and provide mineral nutrition,
and irrigation in order to boost crop yield for ever-increasing demand has caused
serious damage to soil health, and altered ecosystem dynamics (Guignard et al.
2017). The founding principles of first green-revolution thus have serious environmental limitations and repercussions. Advancements in understanding molecular
basis of mineral nutrient uptake by plants, transport and assimilation into the
biological system, coupled with insights into plant development such as that of
root system architecture, and understanding physiological basis of nutrient uptake
have opened up newer vistas. Identification of transporter families, transcription
factors, and regulatory microRNAs involved in uptake and plant development,
coupled with genomic and breeding strategies such as reverse genetics or transgenic
technologies, genome editing, and marker-assisted breeding and selection has the
potential to significantly increase nutrient uptake, transport and assimilation
efficiencies in not only model plants but in crop species.
Acknowledgements The award of JRF/SRF from UGC and DBT to EB, and JRF from CSIR to
RS is gratefully acknowledged. Research in our laboratory is funded by Department of
5 Plant Roots and Mineral Nutrition: An Overview of Molecular Basis of Uptake and. . . 167