Minimum Synthetic Inducible Promoters for Host Response to Parasitic Plants

Parasitic plants are a problem for world agriculture as their direct feeding on hosts can cause high yield losses. One approach to controlling parasitic plants would be to engineer host plants for resistance by expressing an effective defense in response to invasion by the parasite. While much attention has focused on identifying suitable resistance genes, little work has addressed the challenge of identifying promoters to drive specific expression of such genes. To meet this need, we set out to develop a parasite-inducible promoter. Starting with previously generated RNAseq data from Arabidopsis thaliana parasitized by Cuscuta campestris, we identified host genes induced by the parasite and then studied their regulatory regions to identify cis-regulatory elements (CREs). These elements, or transcription factor binding sites (TFBSs), were recombined into a set of minimum synthetic inducible promoters (MSIPs), fused to the β-glucuronidase (GUS) reporter gene, and stably transformed into A. thaliana. The MSIP lines were evaluated with and without Cuscuta, and GUS staining showed that most of the MSIPs were induced by Cuscuta parasitism, although they were also expressed in some non-parasitized tissues. The most parasite-specific MSIP contained stress-inducible TFBSs, and was also responsive to wounding, crushing and jasmonate treatment. Furthermore, A. thaliana parasitized by the root parasite Phelipanche aegyptiaca showed similar MSIP induction patterns in roots, suggesting that at least two types of parasitic plant trigger the same host transcriptional machinery. These MSIPs provide insights into host-parasite interactions and are potentially valuable for driving expression of novel parasite resistance genes.