Risk versus reward: host dependent parasite mortality rates and phenotypes in the facultative generalist Triphysaria versicolor

Abstract

Background: Parasitic plants engage in a complex molecular dialog with potential host plants to identify a host and overcome host defenses to initiate development of the parasitic feeding organ, the haustorium, invade host tissues, and withdraw water and nutrients. While one of two critical signaling events in the parasitic plant life cycle (germination via stimulant chemicals) has been relatively well-studied, the signaling event that triggers haustorium formation remains elusive. Elucidation of this poorly understood molecular dialogue will shed light on plant-plant communication, parasitic plant physiology, and the evolution of parasitism in plants.

Results: Here we present an experimental framework that develops easily quantifiable contrasts for the facultative generalist parasitic plant, Triphysaria, as it feeds across a broad range of diverse flowering plants. The contrasts, including variable parasite growth form and mortality when grown with different hosts, suggest a dynamic and host-dependent molecular dialogue between the parasite and host. Finally, by comparing transcriptome datasets from attached versus unattached parasites we gain insight into some of the physiological processes that are altered during parasitic behavior including shifts in photosynthesis-related and stress response genes.

Conclusions: This work sheds light on Triphysaria's parasitic life habit and is an important step towards understanding the mechanisms of haustorium initiation factor perception, a unique form of plant-plant communication.

Fig. 1

The characteristics of Triphysaria grown across its host range are significantly different from host-free plants and are often highly correlated. ANOVA (Dunnett-Hsu correction) statistical significance compared to the control *p < 0.05 and **p < 0.01. S=Solanum, Z = Zea, M = Medicago, A = Arabidopsis, J = Juncus, O=Oryza, C = host-free control. Pearson’s R² for A vs. E = 0.86, D vs. E = 0.69

Fig. 2

Triphysaria displays host dependent phenotypes. Representative images of Triphysaria showing the average number of surviving plants in each treatment, plus controls. The host genus is listed above each set of parasites. The control plants were grown in identical conditions, in an identical circular arrangement, but without hosts

Fig. 3

The “plump” phenotype is dependent on direct host contact. a experimental design, Sl = S. lycopersicum, Tv = T. versicolor, NC = negative control; b box plot of area:perimeter ratios for all parasites in the experiment; c & d example Triphysaria images from pot SlTv (parasite + host) and Tv (parasite only) showing the “plump” phenotype that parasites display when grown with S. lycopersicum hosts. ANOVA (Tukey-Kramer correction) *p < 0.001