Actinoplanes missouriensiss is a rare actinomycete that forms terminal sporangia containing a few hundred flagellated, motile spores (shown here in a scanning EM image). The TcrA response regulator controls sporangium formation and flagellar biogenesis through the activation of dozens of genes, including three encoding FliA ‐family sigma factors. For details, see the article by Mouri et al. on pp. 718–733 of this issue.