Gene complementation analysis suggests that dodder plants (Cuscutaspp.) do not depend on the host FT protein for flowering

Dodder (Cuscutaspp.) is a genus of parasitic plants that form physiological bridges (haustoria) with their hosts to facilitate the transfer of water and nutrients. The parasites also repurpose nucleic acids and proteins translocating through the haustoria, potentially including the host florigen protein (FT), which is postulated to trigger floral transition in the parasite. Here, we identified the endogenous FT-FD flowering module inCuscuta campestris. We detected the expression of two parasite-encodedC. campestris(Cc)FT genes in haustoria, whereas a newly found CcFD-like gene was expressed ubiquitously.C. campestrisflowered while growing on mutant tobacco plants lacking the floral activators NtFT4 and NtFT5, indicating that host FT proteins are not required to initiate the parasite’s floral transition. We also showed that CcFT1 (identical to CaFT fromCuscuta australis) and CcFT2 can rescue a non-floweringNtft4⁻Ntft5⁻double knockout tobacco phenotype. Together, our results show thatCuscutaspp. produce a potent endogenous florigen as well as other proteins likely to be involved in floral transition. FT gene expression profiles in the haustoria suggest thatCuscutaspp. transition to flowering at least partly in response to host signals (e.g., sugars) that can activate the parasite’s FT-FD module. AlthoughC. campestrisandC. australisappear not to depend on the host FT protein for floral transition, the nature of the mobile host signals that influence floral development in these parasites remain unclear.