UC Davis

Parasitic plants have evolved the ability to recognize neighboring plants and invade their tissues to acquire resources. We hypothesize that the mechanisms used by parasitic plant roots to recognize neighboring plant roots are a specialized adaptation of a general phenomenon that happens in most plants. In Chapter 2, I analyzed the transcriptional regulation of host recognition and prehaustorium development in Triphysaria versicolor using RNASeq. Promoter elements enriched in host-responsive genes were identified and evaluated using a fluorescent reporting construct. Seven elements showed clear tissue specific regulation in Triphysaria. The spatial regulation of five elements was strongly conserved in the two non-parasitic plants Arabidopsis and Mimulus. One element enhanced transcription of our fluorescent reporter in response to the host derived compound DMBQ. In Chapter 3, I show the TvQR1 promoter contains DMBQ responsive and tissue specific elements with conserved activities in two non-parasitic plants. The lack of up-regulation in the endogenous QR1 genes of these non-parasites suggests Triphysaria has co-opted the expression of QR1 for haustorium formation using conserved cis-elements. Lastly, as described in Chapter 4, I tested a Host Induced Gene Silencing approach to control the parasitic weed Phelipanche aegyptiaca. This method yielded a modest reduction in transcripts for four lipid biosynthesis genes but did not sufficiently suppress parasite growth for agricultural application. Together, this work contributes to the understanding of plant-plant interactions through studying the transcriptional regulation of host recognition in a parasitic plant and its conserved aspects in non-parasitic plants. It also yields possible applications for engineering patterns of gene expression in plants and gives insights into controlling parasitic weeds.