MdMYB58 Modulates Fe Homeostasis by Directly Binding to the MdMATE43 Promoter in Plants

Abstract

Nutrient element deprivation, such as iron (Fe) deficiency stress, is a major factor limiting plant survival and proliferation in marginal soils. To cope with a low Fe environment, plants have evolved elaborate mechanisms underlying Fe homeostasis via intricate transcriptional and post-transcriptional regulation. Here, we characterized the Fe deficiency-inducible MYB transcription factor MdMYB58 in apple plants. Overexpressing MdMYB58 resulted in the accumulation of Fe in the root of transgenic Arabidopsis and apple calli when they were exposed to low Fe available conditions. Further investigation revealed that MdMYB58 bound to the promoter of MdMATE43, and its homologue FRD3 in Arabidopsis. Transient expression and stable transgenic assays in apple calli indicated that MdMYB58 transcriptionally repressed MdMATE43 mRNA, as well as FRD3 in Arabidopsis. Interestingly, AtMYB58, the homologue of MdMYB58, possessed higher binding activities to MdMATE43 and FRD3, which suggests a potentially conserved feature of MYB58 binding to MATE transporters in plants. Additionally, MYB-MATE-mediated regulation of Fe homeostasis may be related to the PYE-related Fe deficiency regulatory network via MdSAT1, a member of the IVa subfamily of bHLH transcription factors. Co-overexpression of MdSAT1 competitively weakened MdMYB58-overexpression induced repression of MdMATE43 transcript abundancy by protein-protein interaction. Taken together, the newly identified MYB-bHLH transcription factor expands our understanding of multilevel molecular mechanisms that plants use to coordinate Fe demand with Fe uptake, transport, and tissue partitioning under low Fe conditions.

Regulation of Gene Expression of Methionine Sulfoxide Reductases and Their New Putative Roles in Plants

“…Similarly, the promoter of AtMsrB9 contains 42 binding sites for MYB-type TFs, including binding sites for MYB49, MYB52, and MYB96, which act under water stress [62,63,64], and 35 binding sites for NAC-type TFs, including dehydration-related NAC096 [65]. The NAC-type TFs IDEF1/IDEF2, which are similar to MYB58 [66], are linked to iron deficiency in plants [67]. Therefore, Msrs might be susceptible players in the regulation of redox-sensitive elements.…”

The Transcriptional Control of Iron Homeostasis in Plants: A Tale of bHLH Transcription Factors?

“…A closely related apple R2R3-MYB, MdMYB58, was recently reported as potentially involved in the control of Fe transport and tissue partitioning. It is proposed that MdMYB58 activity is repressed by its heterodimerization with MdSAT1, a clade IVa bHLH (Wang et al, 2018). WRKY46 plays a critical role in Fe translocation from root to shoot by directly repressing the expression of VITL1/VTL1 ( vacuolar iron transporter like 1 ) (Yan et al, 2016).…”

IRONing out stress problems in crops: a homeostatic perspective

“…In Arabidopsis , WRKY46 regulates Fe translocation by repressing the VITL1/VTL1 (VACUOLAR IRON TRANSPORTER LIKE 1) expression (Yan et al 2016) while AP2(ERF TFs) negatively regulates Fe uptake by perturbing the expression of Fe uptake genes like IRT1 or AHA2 (Liu et al 2017a, 2017b). The R2R3‐MYB, MdMYB58 TFs have been found to regulate transport and partitioning of Fe in apple (Wang et al 2018), and so are the FIT‐dependent expression of MYB72, MYB10 and two R2R3‐MYB TFs (Palmer et al 2013, Stringlis et al 2018). Furthermore, ethylene signaling TFs, namely the ETHYLENE INSENSITIVE 3 (EIN3) and ETHYLENE INSENSITIVE 3 LIKE1 (EIL1) regulate FIT stability and thereby playe a major role in the regulation of Fe homeostasis, especially under Fe‐deficiency conditions (Lingam et al 2011).…”