Host-Parasite-Bacteria Triangle: The Microbiome of the Parasitic Weed Phelipanche aegyptiaca and Tomato-Solanum lycopersicum (Mill.) as a Host

Abstract

Broomrapes (Phelipanche/Orobanche spp.) are holoparasitic plants that subsist on the roots of a variety of agricultural crops, establishing direct connections with the host vascular system. This connection allows for the exchange of various substances and a possible exchange of endophytic microorganisms that inhabit the internal tissues of both plants. To shed some light on bacterial interactions occurring between the parasitic Phelipanche aegyptiaca and its host tomato, we characterized the endophytic composition in the parasite during the parasitization process and ascertained if these changes were accompanied by changes to endophytes in the host root. Endophyte communities of the parasitic weed were significantly different from that of the non-parasitized tomato root but no significant differences were observed between the parasite and its host after parasitization, suggesting the occurrence of bacterial exchange between these two plants. Moreover, the P. aegyptiaca endophytic community composition showed a clear shift from gram negative to gram-positive bacteria at different developmental stages of the parasite life cycle. To examine possible functions of the endophytic bacteria in both the host and the parasite plants, a number of unique bacterial candidates were isolated and characterized. Results showed that a Pseudomonas strain PhelS10, originating from the tomato roots, suppressed approximately 80% of P. aegyptiaca seed germination and significantly reduced P. aegyptiaca parasitism. The information gleaned in the present study regarding the endophytic microbial communities in this unique ecological system of two plants connected by their vascular system, highlights the potential of exploiting alternative environmentally friendly approaches for parasitic weed control.

Microbiome facilitated pest resistance: potential problems and uses

“…Although they are being promoted as environmentally friendly and natural, there is no guarantee that the chemicals they make are safe, and it is presumed that regulatory authorities will scrutinize them as they do synthetic pesticides. A Pseudomonas strain infecting tomato reduced germination of the parasitic weed Phelipanche aegyptiaca by 80% . This weed can produce tens of thousands of seeds per plant, so this is insufficient at present to be useful in pest management.…”

The bacterial microbiota of a parasitic plant and its host

“…Holoparasitic plants obtain their requisite energy, nutrients, and water from their hosts 391 by way of haustoria, which also allow symplastic and apoplastic transfer of nucleic acids, 392 proteins, and microorganisms (LeBlanc et al, 2012;Spallek et al, 2017). Consequently, 393 the assembly of parasitic plant microbiota is likely shaped by factors associated with 394 host plants (Sheng-Liang et al, 2014;Kruh et al, 2017;Cui et al, 2018). In this study, 395…”

“…1A-C), and reduction in chloroplast genome size. However, very few 52 studies have investigated changes induced in the composition and assembly of parasitic 53 plant-associated microbial communities (Kruh et al, 2017) in spite of the mounting 54 evidence that such communities are crucial for plant function and fitness (Vogel et al, 55 2016;Castrillo et al, 2017;Fitzpatrick et al, 2018). 56 57 Parasitic plants may also shape the microbiota of their host.…”

“…5; 400 Table S6). Instead, the haustorial transfer of microorganisms or plant-derived molecules, 401 which may act to structure microbiota occurring in both Orobanche roots and leaves, 402 could drive this congruence (Kruh et al, 2017). Though we cannot exclude the 403 possibility that Orobanche may be shaping the microbiota of their hosts, we think it 404 unlikely due to the predominantly (albeit not exclusively) one-way flow of haustorial 405 transfer from host to parasite (Serghini et al, 2001).…”

“…Phytohabitans was reduced in only directly infected roots, while Flavobacterium was 446 reduced in both infected and uninfected roots from infected individuals, indicative of 447 systemic effects of infection on Hedera root microbiota. Kruh et al, (2017) found that 448…”