CdnL is an essential RNA polymerase (RNAP)-binding activator of rRNA transcription in mycobacteria and myxobacteria but reportedly not in Bacillus. Whether its function and mode of action are conserved in other bacteria thus remains unclear. Because virtually all alphaproteobacteria have a CdnL homolog and none of these have been characterized, we studied the homolog (CdnL _Cc ) of the model alphaproteobacterium Caulobacter crescentus. We show that CdnL _Cc is not essential for viability but that its absence or depletion causes slow growth and cell filamentation. CdnL _Cc is degraded in vivo in a manner dependent on its C-terminus, yet excess CdnL _Cc resulting from its stabilization did not adversely affect growth. We find that CdnL _Cc interacts with itself and with the RNAP β subunit, and localizes to at least one rRNA promoter in vivo, whose activity diminishes upon depletion of CdnL _Cc . Interestingly, cells expressing CdnL _Cc mutants unable to interact with the RNAP were cold-sensitive, suggesting that CdnL _Cc interaction with RNAP is especially required at lower than standard growth temperatures in C. crescentus. Our study indicates that despite limited sequence similarities and regulatory differences compared to its myco/myxobacterial homologs, CdnL _Cc may share similar biological functions, since it affects rRNA synthesis, probably by stabilizing open promoter-RNAP complexes.