AUTHOR=Huo Liuqing , Guo Zijian , Zhang Zhijun , Jia Xin , Sun Yiming , Sun Xun , Wang Ping , Gong Xiaoqing , Ma Fengwang 

TITLE=The Apple Autophagy-Related Gene MdATG9 Confers Tolerance to Low Nitrogen in Transgenic Apple Callus

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.00423

DOI=10.3389/fpls.2020.00423

ISSN=1664-462X

ABSTRACT=<p>Autophagy is an efficient degradation system for maintaining cellular homeostasis when plants are under environmental stress. ATG9 is the only integral membrane protein within the core ATG machinery that provides a membrane source for autophagosome formation. In this study, we isolated an <italic>ATG9</italic> homologs gene in apple, <italic>MdATG9</italic>, from <italic>Malus domestica</italic>. The analysis of its sequence, subcellular localization, promoter cis-elements, and expression patterns revealed the potential function of <italic>MdATG9</italic> in response to abiotic stressors. Overexpression of <italic>MdATG9</italic> in apple callus conferred enhanced tolerance to nitrogen depletion stress. During the treatment, other important <italic>MdATG</italic>s were expressed at higher levels in transgenic callus than in the wild type. Furthermore, more free amino acids and increased sucrose levels were found in <italic>MdATG9</italic>-overexpression apple callus compared with the wild type in response to nitrogen starvation, and the expression levels of <italic>MdNRT1.1</italic>, <italic>MdNRT2.5</italic>, <italic>MdNIA1</italic>, and <italic>MdNIA2</italic> were all increased higher in transgenic lines. These data suggest that, as an important autophagy gene, <italic>MdATG9</italic> plays an important role in the maintenance of amino acids and sugars in response to nutrient starvation in apple.</p>