AUTHOR=Ishfaq Muhammad , Zhong Yanting , Wang Yongqi , Li Xuexian 

TITLE=Magnesium Limitation Leads to Transcriptional Down-Tuning of Auxin Synthesis, Transport, and Signaling in the Tomato Root

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.802399

DOI=10.3389/fpls.2021.802399

ISSN=1664-462X

ABSTRACT=<p>Magnesium (Mg) deficiency is becoming a widespread limiting factor for crop production. How crops adapt to Mg limitation remains largely unclear at the molecular level. Using hydroponic-cultured tomato seedlings, we found that total Mg<sup>2+</sup> content significantly decreased by ∼80% under Mg limitation while K<sup>+</sup> and Ca<sup>2+</sup> concentrations increased. Phylogenetic analysis suggested that Mg transporters (MRS2/MGTs) constitute a previously uncharacterized 3-clade tree <italic>in planta</italic> with two rounds of asymmetric duplications, providing evolutionary evidence for further molecular investigation. In adaptation to internal Mg deficiency, the expression of six representative <italic>MGT</italic>s (two in the shoot and four in the root) was up-regulated in Mg-deficient plants. Contradictory to the transcriptional elevation of most of <italic>MGT</italic>s, Mg limitation resulted in the ∼50% smaller root system. Auxin concentrations particularly decreased by ∼23% in the Mg-deficient root, despite the enhanced accumulation of gibberellin, cytokinin, and ABA. In accordance with such auxin reduction was overall transcriptional down-regulation of thirteen genes controlling auxin biosynthesis (<italic>TAR</italic>/<italic>YUCs</italic>), transport (<italic>LAXs, PINs</italic>), and signaling (<italic>IAAs, ARFs</italic>). Together, systemic down-tuning of gene expression in the auxin signaling pathway under Mg limitation preconditions a smaller tomato root system, expectedly stimulating <italic>MGT</italic> transcription for Mg uptake or translocation.</p>