The Plant Growth-Promoting Fungus MF23 (Mycena sp.) Increases Production of Dendrobium officinale (Orchidaceae) by Affecting Nitrogen Uptake and NH4+ Assimilation
Ting-Ting Shan, Lisi Zhou, Bing Li, Xiaomei Chen, Shun‐Xing Guo, Airong Wang, Lixia Tian, Jingting Liu
Abstract
Dendrobium officinale Kimura et Migo is a traditional and scarce medicinal orchid in China. Mycorrhizal fungi could supply nitrogen (N) to orchids for seed germination and seedling recruitment. However, the N transport mechanism between orchids and the fungus is poorly understand. Early studies found that the fungus MF23 ( Mycena sp.) could promote the growth of D. officinale . To better dissect the molecular interactions involved in N transport between D. officinale and MF23, transcriptome and metabolome analyses were conducted on conventional and mycorrhizal cultivations of D. officinale . Moreover, validation tests were carried out in the greenhouse to measure net fluxes of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msubsup><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn><mml:mo>−</mml:mo></mml:msubsup></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msubsup><mml:mi mathvariant="normal">H</mml:mi><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math> of roots by a non-invasive micro-test technology (NMT), determine N assimilation enzyme activity by the ELISA, and analyze the expression level of differentially expressed genes (DEGs) of N transporters and DEGs involved in N metabolism by RT-qPCR. Combined transcriptome and metabolome analyses showed that MF23 may influence N metabolism in D. officinale . The expression of DoNAR2.1 (nitrate transporter-activating protein), DoAMT11 (ammonium transporter), DoATFs (amino acid transporters), DoOPTs (oligopeptide transporters), and DoGDHs (glutamate dehydrogenases) in symbiotic D. officinale was upregulated. NMT results showed a preference for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msubsup><mml:mi mathvariant="normal">H</mml:mi><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math> in D. officinale and indicated that MF23 could promote the uptake of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msubsup><mml:mi mathvariant="normal">O</mml:mi><mml:mn>3</mml:mn><mml:mo>−</mml:mo></mml:msubsup></mml:mrow></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M6"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msubsup><mml:mi mathvariant="normal">H</mml:mi><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math> , especially for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M7"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msubsup><mml:mi mathvariant="normal">H</mml:mi><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math> . ELISA results showed that MF23 could increase the activity of glutamine synthetase (GS) and glutamate dehydrogenase. This study suggested that MF23 increases the production of D. officinale by affecting N uptake and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M8"><mml:mrow><mml:mi mathvariant="normal">N</mml:mi><mml:msubsup><mml:mi mathvariant="normal">H</mml:mi><mml:mn>4</mml:mn><mml:mo>+</mml:mo></mml:msubsup></mml:mrow></mml:math> assimilation capacity.