AUTHOR=Li Yang , Li Juanqi , Yan Yan , Liu Wenqian , Zhang Wenna , Gao Lihong , Tian Yongqiang 

TITLE=Knock-Down of CsNRT2.1, a Cucumber Nitrate Transporter, Reduces Nitrate Uptake, Root length, and Lateral Root Number at Low External Nitrate Concentration

JOURNAL=Frontiers in Plant Science

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.00722

DOI=10.3389/fpls.2018.00722

ISSN=1664-462X

ABSTRACT=<p>Nitrogen (N) is a macronutrient that plays a crucial role in plant growth and development. Nitrate (<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal" mathcolor="black">NO</mml:mi><mml:mi mathvariant="normal" mathcolor="black">3</mml:mi><mml:mn mathvariant="normal" mathcolor="black">-</mml:mn></mml:msubsup></mml:math></inline-formula>) is the most abundant N source in aerobic soils. Plants have evolved two adaptive mechanisms such as up-regulation of the high-affinity transport system (HATS) and alteration of the root system architecture (RSA), allowing them to cope with the temporal and spatial variation of <inline-formula><mml:math id="M26" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal" mathcolor="black">NO</mml:mi><mml:mi mathvariant="normal" mathcolor="black">3</mml:mi><mml:mn mathvariant="normal" mathcolor="black">-</mml:mn></mml:msubsup></mml:math></inline-formula>. However, little information is available regarding the nitrate transporter in cucumber, one of the most important fruit vegetables in the world. In this study we isolated a nitrate transporter named <italic>CsNRT2.1</italic> from cucumber. Analysis of the expression profile of the <italic>CsNRT2.1</italic> showed that <italic>CsNRT2.1</italic> is a high affinity nitrate transporter which mainly located in mature roots. Subcellular localization analysis revealed that CsNRT2.1 is a plasma membrane transporter. In N-starved <italic>CsNRT2.1</italic> knock-down plants, both of the constitutive HATS (cHATS) and inducible HATS (iHATS) were impaired under low external <inline-formula><mml:math id="M28" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal" mathcolor="black">NO</mml:mi><mml:mi mathvariant="normal" mathcolor="black">3</mml:mi><mml:mn mathvariant="normal" mathcolor="black">-</mml:mn></mml:msubsup></mml:math></inline-formula> concentration. Furthermore, the <italic>CsNRT2.1</italic> knock-down plants showed reduced root length and lateral root numbers. Together, our results demonstrated that CsNRT2.1 played a dual role in regulating the HATS and RSA to acquire <inline-formula><mml:math id="M29" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi mathvariant="normal" mathcolor="black">NO</mml:mi><mml:mi mathvariant="normal" mathcolor="black">3</mml:mi><mml:mn mathvariant="normal" mathcolor="black">-</mml:mn></mml:msubsup></mml:math></inline-formula> effectively under N limitation.</p>