AUTHOR=Shan Tingting , Zhou Lisi , Li Bing , Chen Xiaomei , Guo Shunxing , Wang Airong , Tian Lixia , Liu Jingting 

TITLE=The Plant Growth-Promoting Fungus MF23 (Mycena sp.) Increases Production of Dendrobium officinale (Orchidaceae) by Affecting Nitrogen Uptake and NH4+ Assimilation

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.693561

DOI=10.3389/fpls.2021.693561

ISSN=1664-462X

ABSTRACT=<p><italic>Dendrobium officinale</italic> 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 (<italic>Mycena</italic> sp.) could promote the growth of <italic>D. officinale</italic>. To better dissect the molecular interactions involved in N transport between <italic>D. officinale</italic> and MF23, transcriptome and metabolome analyses were conducted on conventional and mycorrhizal cultivations of <italic>D. officinale</italic>. Moreover, validation tests were carried out in the greenhouse to measure net fluxes of <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><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></inline-formula> and <inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><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></inline-formula> 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 <italic>D. officinale</italic>. The expression of <italic>DoNAR2.1</italic> (nitrate transporter-activating protein), <italic>DoAMT11</italic> (ammonium transporter), <italic>DoATFs</italic> (amino acid transporters), <italic>DoOPTs</italic> (oligopeptide transporters), and <italic>DoGDHs</italic> (glutamate dehydrogenases) in symbiotic <italic>D. officinale</italic> was upregulated. NMT results showed a preference for <inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><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></inline-formula> in <italic>D. officinale</italic> and indicated that MF23 could promote the uptake of <inline-formula><mml:math id="M5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><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></inline-formula> and<inline-formula><mml:math id="M6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><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></inline-formula>, especially for <inline-formula><mml:math id="M7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><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></inline-formula>. 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 <italic>D. officinale</italic> by affecting N uptake and <inline-formula><mml:math id="M8" xmlns:mml="http://www.w3.org/1998/Math/MathML"><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></inline-formula> assimilation capacity.</p>