Genomic and Epigenomic Mechanisms of the Interaction between Parasitic and Host Plants

Exploring Information Exchange between Thesium chinense and Its Host Prunella vulgaris through Joint Transcriptomic and Metabolomic Analysis

BACKGROUND

Thesium chinense known as the "plant antibiotic" is a facultative root hemi-parasitic herb while Prunella vulgaris can serve as its host. However, the molecular mechanisms underlying the communication between T. chinense and its host remained largely unexplored. The aim of this study was to provide a comprehensive view of transferred metabolites and mobile mRNAs exchanged between T. chinense and P. vulgaris.

RESULTS

The wide-target metabolomic and transcriptomic analysis identified 5 transferred metabolites (ethylsalicylate, eriodictyol-7-O-glucoside, aromadendrin-7-O-glucoside, pruvuloside B, 2-ethylpyrazine) and 50 mobile genes between T. chinense and P. vulgaris, as well as haustoria formation related 56 metabolites and 44 genes. There were 4 metabolites (ethylsalicylate, eriodictyol-7-O-glucoside, aromadendrin-7-O-glucoside and pruvuloside B) that are transferred from P. vulgaris to T. chinense, whereas 2-ethylpyrazine was transferred in the opposite direction. Furthermore, we inferred a regulatory network potentially involved in haustoria formation, where three metabolites (N,N'-Dimethylarginine/SDMA, NG,NG-Dimethyl-L-arginine, 2-Acetoxymethyl-anthraquinone) showed significant positive correlations with the majority of haustoria formation-related genes.

CONCLUSIONS

These results suggested that there was an extensive exchange of information with P. vulgaris including transferred metabolites and mobile mRNAs, which might facilitate the haustoria formation and parasition of T. chinense.

Invited Review Beyond parasitic convergence: unravelling the evolution of the organellar genomes in holoparasites

BACKGROUND

The molecular evolution of organellar genomes in angiosperms has been studied extensively, with some lineages, such as parasitic ones, displaying unique characteristics. Parasitism has emerged 12 times independently in angiosperm evolution. Holoparasitism is the most severe form of parasitism, and is found in ~10 % of parasitic angiosperms. Although a few holoparasitic species have been examined at the molecular level, most reports involve plastomes instead of mitogenomes. Parasitic plants establish vascular connections with their hosts through haustoria to obtain water and nutrients, which facilitates the exchange of genetic information, making them more susceptible to horizontal gene transfer (HGT). HGT is more prevalent in the mitochondria than in the chloroplast or nuclear compartments.

SCOPE

This review summarizes current knowledge on the plastid and mitochondrial genomes of holoparasitic angiosperms, compares the genomic features across the different lineages, and discusses their convergent evolutionary trajectories and distinctive features. We focused on Balanophoraceae (Santalales), which exhibits extraordinary traits in both their organelles.

CONCLUSIONS

Apart from morphological similarities, plastid genomes of holoparasitic plants also display other convergent features, such as rampant gene loss, biased nucleotide composition and accelerated evolutionary rates. In addition, the plastomes of Balanophoraceae have extremely low GC and gene content, and two unexpected changes in the genetic code. Limited data on the mitochondrial genomes of holoparasitic plants preclude thorough comparisons. Nonetheless, no obvious genomic features distinguish them from the mitochondria of free-living angiosperms, except for a higher incidence of HGT. HGT appears to be predominant in holoparasitic angiosperms with a long-lasting endophytic stage. Among the Balanophoraceae, mitochondrial genomes exhibit disparate evolutionary paths with notable levels of heteroplasmy in Rhopalocnemis and unprecedented levels of HGT in Lophophytum. Despite their differences, these Balanophoraceae share a multichromosomal mitogenome, a feature also found in a few free-living angiosperms.