AUTHOR=Chen Yakun , Zheng Qingbo , Jia Xiaolin , Chen Keqin , Wang Yi , Wu Ting , Xu Xuefeng , Han Zhenhai , Zhang Zhihong , Zhang Xinzhong 

TITLE=MdGGT1 Impacts Apple miR156 Precursor Levels via Ontogenetic Changes in Subcellular Glutathione Homeostasis

JOURNAL=Frontiers in Plant Science

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2019.00994

DOI=10.3389/fpls.2019.00994

ISSN=1664-462X

ABSTRACT=<p>The vegetative phase change in flowering plants is controlled by microRNA156 (miR156) under transcriptional regulation. However, the developmental signals upstream of miR156 are not well understood. The glutathione/glutathione disulfide (GSH/GSSG) ratios and GSH levels decline significantly during phase change, which is consistent with miR156 expression in apple (<italic>Malus domestica</italic> Borkh.). Here, we found that the content of protein conjugated glutathione was remarkably higher in chloroplasts and nuclei of adult than juvenile phase apple hybrids. The decrease in miR156 expression was most relevant to the activities of serine acetyltransferase (SAT) and soluble γ-glutamyl transpeptidase (GGT), and the expressions of <italic>MdGGT1</italic> or <italic>MdSATs</italic>. Transgenic apples over-expressing <italic>MdMIR156</italic> or miR156-mimetic (MIM156) did not alter <italic>MdGGT1</italic> expression or the soluble GGT activity. Inhibition of GGT activity with serine-borate complex or acivicin led to significant reduction in GSH content, the GSH/GSSG ratio, and the expressions of <italic>MdMIR156a5</italic>, <italic>MdMIR156a12</italic>, and miR156. Depletion of GSH with diethyl maleate without altering GGT activity caused a dramatic decrease in the expression of <italic>MdMIR156a5</italic>, <italic>MdMIR156a12</italic>, and miR156. Manipulating GGT activity and GSH homeostasis by transgenic over-expressing or RNAi <italic>MdGGT1</italic> increased or decreased <italic>MdMIR156a5</italic> and <italic>MdMIR156a12</italic> levels, respectively. These data provided novel evidence that <italic>MdGGT1</italic> participates in transcriptional level of transcription regulation of miR156 precursors during ontogenesis.</p><sec><title>HIGHLIGHTS</title><p>- MdGGT1 affects thiol redox status and indirectly participates in the regulation of miR156 expression during vegetative phase change.</p></sec>