The TvPirin gene is necessary for haustorium development in the parasitic plant Triphysaria versicolor

Abstract

The rhizosphere is teemed with organisms that coordinate their symbioses using chemical signals traversing between the host root and symbionts. Chemical signals also mediate interactions between roots of different plants, perhaps the most obvious being those between parasitic Orobanchaceae and their plant hosts. Parasitic plants use specific molecules provided by host roots to initiate the development of haustoria, invasive structures critical for plant parasitism. We took a transcriptomics approach to identify parasitic plant genes associated with host factor recognition and haustorium signaling and previously identified a gene, TvPirin, which is transcriptionally up-regulated in roots of the parasitic plant Triphysaria versicolor after being exposed to the haustorium-inducing molecule 2,6-dimethoxybenzoquinone (DMBQ). Because TvPirin shares homology with proteins associated with environmental signaling in some plants, we hypothesized that TvPirin may function in host factor recognition in parasitic plants. We tested the function of TvPirin in T. versicolor roots using hairpin-mediated RNA interference. Reducing TvPirin transcripts in T. versicolor roots resulted in significantly less haustoria development in response to DMBQ exposure. We determined the transcript levels of other root expressed transcripts and found that several had reduced basal levels of gene expression but were similarly regulated by quinone exposure. Phylogenic investigations showed that TvPirin homologs are present in most flowering plants, and we found no evidence of parasite-specific gene duplication or expansion. We propose that TvPirin is a generalized transcription factor associated with the expression of a number of genes, some of which are involved in haustorium development.

Figure 1.

Pirin phylogeny. The phylogeny of the Pirin gene family was derived from sequence data of 10 fully sequenced plant genomes together with sequences from the PPGP (shaded and labeled PPGP). The TvPirin gene described in this manuscript is marked with a star. [See online article for color version of this figure.]

Figure 2.

Transcriptional regulation of TvPirin. RNA was extracted from T. versicolor seedlings after exposure to water, DMBQ, or M. truncatula (host) roots for 2 h. Steady-state transcript levels of TvPirin were determined by qRT-PCR and normalized to the constitutively expressed gene TvQN8 for each sample. Data are means ± sd of three technical replicates of three biological replicates (n = 9). Each biological replicate was a square petri dish with 20 to 50 seedlings. Expression levels of roots treated with DMBQ was set to 100%. Note the relative expression values are written on top of each bar.

Figure 3.

Gene expression in pHpPRN roots. Steady-state transcript levels of 10 parasite genes in TvPirin-silenced roots were determined by quantitative PCR and normalized to the constitutively expressed gene TvQN8 for each sample. Data are means ± sd of three technical replicates of three to four plants (n = 9–12). Expression levels in pHG8-YFP transgenic roots treated with water was set to 100% and considered as the basal level of expression of the interested gene. Note the log scale y axis.