A transcription factor regulates development of a bacteria-housing eukaryotic cell through DNA damage mitigation.

Intracellular microorganisms are widespread and housed within specialized host cells called bacteriocytes in many invertebrates. Although increasing attention has been devoted to understanding bacteriocyte development, differentiation, and proliferation, the molecular mechanisms that maintain these cells remain poorly understood. We previously showed that the transcription factor Adf-1 suppresses bacteriocyte cell death in whiteflies. Here, DNA affinity purification sequencing identified Adf-1 target genes involved in diverse cellular processes and revealed the DNA damage response kinase ataxia telangiectasia and Rad3-related (ATR) as a direct transcriptional target. Dual-luciferase reporter assays and RNA interference confirmed that Adf-1 binds the ATR promoter and positively regulates its expression in bacteriocytes, where ATR is highly expressed. Consistent with this regulatory relationship, silencing either Adf-1 or ATR increased DNA damage in bacteriocytes. ATR knockdown further promoted apoptosis and autophagy, reduced the proportion of dividing bacteriocytes, decreased bacteriocyte abundance, and lowered symbiont titers in whiteflies. In addition, yeast two-hybrid assays identified an interaction between Adf-1 and the ATP-dependent DNA helicase RecQ1, although RecQ1 silencing had no detectable effect on bacteriocyte abundance. Together, our findings demonstrate that Adf-1 preserves bacteriocyte homeostasis by promoting DNA damage repair through transcriptional activation of ATR. Given that bacteriocytes are exposed to persistent genotoxic stress associated with polyploidy and high metabolic activity, this work identifies DNA damage control as a key mechanism underlying bacteriocyte maintenance and symbiosis stability, and suggests that this pathway may represent a conserved feature of bacteriocyte biology.