The cytokinin oxidase/dehydrogenase TaCKX11-D positively regulates grain size in wheat

Grain size is one of the critical determinants of yield in wheat (Triticum aestivum) and is affected by cytokinin signaling. Cytokinin oxidase/dehydrogenase (CKX) regulates cytokinin homeostasis by catalysing its degradation. In this study, we determined that TaCKX11-D positively regulates wheat grain size. Overexpression of TaCKX11-D significantly increased grain length, width, thickness, and weight in wheat and Arabidopsis, whilst silencing TaCKX11-D in wheat decreased grain size and weight. Cytological analysis revealed that TaCKX11-D affected wheat grain size by regulating the cell size in the outer pericarp. Overexpression of TaCKX11-D was also found to reduce the endogenous cytokinin content in wheat, demonstrating that it promotes cell expansion and increases grain size via regulation of cytokinin homeostasis. Furthermore, we found that TaCKX11-D directly interacts with and is phosphorylated by TaMPK3 and TaMPK6. Our findings provide potentially valuable insights for breeding improved wheat varieties.