Soil inorganic phosphate (Pi) levels are frequently suboptimal for the growth and development of crop plants. Although MADS-box genes participate in diverse plant developmental processes, their involvement in phosphate starvation responses (PSRs) remains unclear. We identified a type I MADS-box transcription factor gene, TaMADS2-3D, which was rapidly induced under low-Pi stress in roots of wheat (Triticum aestivum). A TaMADS2-3D-GFP fusion protein was found located in the nucleus. Transgenic Arabidopsis plants overexpressing TaMADS2-3D (TaMADS2-3DOE) showed shortened primary roots, increased lateral root density, and retarded seedling growth under high-Pi (HP) conditions, accompanied by increased Pi contents in their shoots and roots. The Arabidopsis TaMADS2-3DOE plants showed similar PSR phenotypes under low Pi (LP) conditions. These results indicate constitutive activation of PSRs by overexpression of TaMADS2-3D in Arabidopsis. Reactive oxygen species (ROS), H₂O₂ and O₂⁻, levels were increased in root tips of Arabidopsis TaMADS2-3DOE plants under HP conditions. Transcriptome analysis of Arabidopsis TaMADS2-3DOE plants under different Pi regimes revealed expression changes for a variety of PSR genes including AtZAT6. Overexpression of TaMADS2-3D in wheat also led to constitutive activation of PSRs. We propose that TaMADS2-3D regulates plant PSRs probably by modulating ROS homeostasis, root development, PSR gene expression, and Pi uptake. This study increases our understanding of plant PSR regulation and provides a valuable gene for improving phosphorus-use efficiency in wheat and other crops.

Triticum urartu (AA, 2n = 2x = 14), a wild grass endemic to the Fertile Crescent (FC), is the progenitor of the A subgenome in common wheat. It belongs to the primary gene pool for wheat improvement. Here, we evaluated the yellow rust (caused by Puccinia striiformis f. sp. tritici, Pst) reactions of 147 T. urartu accessions collected from different parts of the FC. The reactions varied from susceptibility to strong resistance. In general, there were more accessions with stronger resistance to race CYR33 than to CYR 32. In most cases the main form of defense was a moderate resistance characterized by the presence of necrotic/chlorotic lesions with fewer Pst uredinia on the leaves. Forty two accessions displayed resistance to both races. Histological analysis showed that Pst growth was abundant in the compatible interaction but significantly suppressed by the resistant response. Gene silencing mediated by Barley stripe mosaic virus was effective in two T. urartu accessions with different resistance responses, indicating that this method can expedite future functional analysis of resistance genes. Our data suggest that T. urartu is a valuable source of resistance to yellow rust, and represents a model for studying the genetic, genomic and molecular basis underlying interaction between wheat and Pst.