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

• Published in: Frontiers in plant science Vol. 12; p. 802399
• Main Authors: Ishfaq, Muhammad, Zhong, Yanting, Wang, Yongqi, Li, Xuexian
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 23.12.2021
• Subjects: auxin; auxin signaling; magnesium limitation; MRS2/MGT gene family; PIN family; Plant Science; root system; magnesium limitation; root system; auxin; MRS2/MGT gene family; PIN family; auxin signaling
• ISSN: 1664-462X; 1664-462X
• DOI: 10.3389/fpls.2021.802399

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 2+ content significantly decreased by ∼80% under Mg limitation while K + and Ca 2+ concentrations increased. Phylogenetic analysis suggested that Mg transporters (MRS2/MGTs) constitute a previously uncharacterized 3-clade tree in planta with two rounds of asymmetric duplications, providing evolutionary evidence for further molecular investigation. In adaptation to internal Mg deficiency, the expression of six representative MGT 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 MGT 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 ( TAR / YUCs ), transport ( LAXs, PINs ), and signaling ( IAAs, ARFs ). Together, systemic down-tuning of gene expression in the auxin signaling pathway under Mg limitation preconditions a smaller tomato root system, expectedly stimulating MGT transcription for Mg uptake or translocation.