| Summary: | Actin plays a critical role in the rhizobium−legume symbiosis. Cytoskeletal rearrangements and changes in actin occur in response to Nod factors secreted by rhizobia during symbiotic interactions with legumes. These cytoskeletal rearrangements are mediated by diverse actin-binding proteins, such as actin depolymerization factors (ADFs). We examined the function of an ADF in the <i>Phaseolus vulgaris</i>−rhizobia symbiotic interaction (<i>PvADFE</i>). <i>PvADFE</i> was preferentially expressed in rhizobia-inoculated roots and nodules. <i>PvADFE</i> promoter activity was associated with root hairs harbouring growing infection threads, cortical cell divisions beneath root hairs, and vascular bundles in mature nodules. Silencing of <i>PvADFE</i> using RNA interference increased the number of infection threads in the transgenic roots, resulting in increased nodule number, nitrogen fixation activity, and average nodule diameter. Conversely, overexpression of <i>PvADFE</i> reduced the nodule number, nitrogen fixation activity, average nodule diameter, as well as <i>NODULE INCEPTION</i> (<i>NIN</i>) and <i>EARLY NODULIN2</i> (<i>ENOD2</i>) transcript accumulation. Hence, changes in <i>ADFE</i> transcript levels affect rhizobial infection and nodulation, suggesting that ADFE is fine-tuning these processes.
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