Actin networks are critical for maintaining integrity and subcellular organization of ukaryotic cells. In this issue, Gavrin and colleagues show that rhizobial symbiosomes in nitrogen-fixing legume root nodules are surrounded by nets of actin microfilaments. The ARP3 protein, known to be required for formation of microfilament branches, is also required for proper symbiosome development, demonstrating the importance of actin microfilaments in symbiosome development.