| Summary: | Fabaceans symbiotically interact with nitrogen-fixing rhizobacteria to form root nodules. Some fabacean specific proteins play important roles in the symbiosis. WRKY-related Protein (WRP) is a novel fabacean specific protein, whose functions have not been well characterized. In this study, MtWRP1 was functionally characterized in <i>Medicago truncatula</i>. It contains a WRKY domain at C-terminal and a novel transmembrane (TM) domain at N-terminal, and its WRKY domain was highly similar to the N-terminal WRKY domain of the group I WRKY proteins. The TM domain was highly homologous to the eukaryotic cytochrome b561 (Cytb561) proteins from birds. Subcellular localization revealed that MtWRP1 was targeted to the Golgi apparatus through the novel TM domain. <i>MtWRP1</i> was highly expressed in roots and nodules, suggesting its possible roles in the regulation of root growth and nodulation. Both <i>MtWRP1</i>-overexpression transgenic <i>M. truncatula</i> and <i>MtWRP1</i> mutants showed altered root nodulation and plant growth performance. Specifically, the formation of root nodules was significantly reduced in the absence of <i>MtWRP1</i>. These results demonstrated that <i>MtWRP1</i> plays critical roles in root nodulation and plant growth.
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