Tonoplast-localized transporter ZmNRAMP2 confers root-to-shoot translocation of manganese in maize

Abstract

Almost all living organisms require manganese (Mn) as an essential trace element for survival. To maintain an irreplaceable role in the oxygen-evolving complex of photosynthesis, plants require efficient Mn uptake in roots and delivery to above-ground tissues. However, the underlying mechanisms of root-to-shoot Mn translocation remain unclear. Here, we identified an Natural Resistance Associated Macrophage Protein (NRAMP) family member in maize (Zea mays), ZmNRAMP2, which localized to the tonoplast in maize protoplasts and mediated transport of Mn in yeast (Saccharomyces cerevisiae). Under Mn deficiency, two maize mutants defective in ZmNRAMP2 exhibited remarkable reduction of root-to-shoot Mn translocation along with lower shoot Mn contents, resulting in substantial decreases in Fv/Fm and plant growth inhibition compared to their corresponding wild-type (WT) plants. ZmNRAMP2 transcripts were highly expressed in xylem parenchyma cells of the root stele. Compared to the WT, the zmnramp2-1 mutant displayed lower Mn concentration in xylem sap accompanied with retention of Mn in root stele. Furthermore, the overexpression of ZmNRAMP2 in transgenic maize showed enhanced root-to-shoot translocation of Mn and improved tolerance to Mn deficiency. Taken together, our study reveals a crucial role of ZmNRAMP2 in root-to-shoot translocation of Mn via accelerating vacuolar Mn release in xylem parenchyma cells for adaption of maize plants to low Mn stress and provides a promising transgenic approach to develop low Mn-tolerant crop cultivars.

ZmHMA3, a Member of the Heavy-Metal-Transporting ATPase Family, Regulates Cd and Zn Tolerance in Maize

“…Quantitative analysis revealed that ZmHMA3 had h expression in B73 roots than in Mo17 (Figure 2A). ZmHMA3 was upregulated in root stems under Cd stress, and this result is similar to previous studies on OsHMA2, AtHM and HvHMA2 [33]. These genes are involved in transporting metals from the subsu…”

“…Quantitative analysis revealed that ZmHMA3 had higher expression in B73 roots than in Mo17 (Figure 2A). ZmHMA3 was upregulated in roots and stems under Cd stress, and this result is similar to previous studies on OsHMA2, AtHMA2, and HvHMA2 [33]. These genes are involved in transporting metals from the subsurface to the above ground, and they have various functions in transporting metals into or out of cells and in loading or unloading metals in the xylem [33,34].…”

MsNRAMP2 Enhances Tolerance to Iron Excess Stress in Nicotiana tabacum and MsMYB Binds to Its Promoter

“…AtNRAMP6 is localized in the plasma membrane and intima, including the endoplasmic reticulum [70]. OsNRAMP2 and ZmNRAMP2 are tonoplast-localized transporters [71,72]. In this study, The MsNRAMP2 protein is located in the whole cell, including the nucleus and cytoplasm but not in the chloroplast (Figure 4).…”

TaNRAMP3 is essential for manganese transport in Triticum aestivum

“…To date, orthologous proteins of AtNRAMP1 have been characterized in various species, such as rice and corn. They are play essential roles in the tolerance to the Mn deficiency condition (Sasaki et al 2012;Ueno et al 2015;Guo et al 2022). Previous research has shown that TpN-RAMP3 in dwarf Polish Wheat (Triticum polonicum L) possesses Mn, Cd, and Co transport activities, and improve tolerance to Mn toxicity in Arabidopsis (Peng et al 2018).…”

“…In rice, OsNRAMP5 is located at the far end of the outer and endodermis cells, and is the main transporter of Mn and Cd, responsible for transporting Mn and Cd from the external solution to the root cells (Sasaki et al 2012;Ueno et al 2015). Recent studies have reported that ZmNRAMP2 in maize is located on tonoplast to mediate Mn transport (Guo et al 2022).…”