Vacuolar zinc transporter TaMTP1 safeguards wheat fertility and regulates grain zinc allocation via stem-mediated sequestration.

Metal tolerance protein 1 (MTP1) is essential for metal homeostasis and detoxification, but its roles in crop fertility and reproductive organ development are poorly understood. Here, we demonstrate that wheat TaMTP1 safeguards reproductive success and grain Zn allocation by mediating vacuolar Zn sequestration in stems. Heterologous expression in yeast and subcellular localization confirmed that TaMTP1 functions as a tonoplast Zn transporter. In wheat, the TaMTP1 gene was highly expressed in developing spikes and stems across all growth stages. Triple knockout mutants (aabbdd) from a TILLING population exhibited sterility, stunted growth, and abnormal pollen and stigma development, particularly under high Zn supply. ICP-OES analysis revealed Zn hyperaccumulation in reproductive tissues due to impaired vacuolar sequestration in stems, leading to excessive Zn translocation to spikes. Fluorescence imaging showed Zn overaccumulation in pollen, and depletion in the phloem of stem vascular bundles. Fertility and normal growth were restored under low Zn condition, confirming that reproductive failure was driven by Zn toxicity rather than deficiency. Single functional TaMTP1 alleles were sufficient to maintain fertility, whereas partial mutants (Aa/AAbbdd and aaBbdd) accumulated elevated Zn in grain under excess Zn supply compared with null. Together, our findings uncover a stem-based vacuolar Zn buffering mechanism that prevents reproductive Zn toxicity, establishing TaMTP1 as a key determinant of fertility and grain Zn partitioning in wheat, with potential for biofortification and Zn resilience breeding.