Holoparasitic Rafflesiaceae possess the most reduced endophytes and yet give rise to the world's largest flowers

Abstract

Rafflesiaceae produce greatly reduced and modified vegetative bodies even when compared with the other holoparasitic angiosperms once grouped with Rafflesiaceae, which possess some vegetative differentiation. Based on previous studies of seeds together with these findings, it is concluded that the endophyte probably develops directly from a proembryo, and not from an embryo proper. Similarly, the flowering shoot arises directly from the undifferentiated endophyte. These filaments produce a protocorm in which a shoot apex originates endogenously by formation of a secondary morphological surface. This degree of modification to the vegetative body is exceptional within angiosperms and warrants additional investigation. Furthermore, the study highlights a mechanical isolation mechanism by which the host may defend itself from the parasite.

The Haustorium, a Specialized Invasive Organ in Parasitic Plants

“…The tree was adapted from the Angiosperm Phylogeny Website (http://www.mobot.org/MOBOT/research/APweb) and the APG III tree (8) first look, facultative parasites are almost indistinguishable from autotrophic plants, whereas some obligate parasitic plants are distinct because of their complete loss of fundamental plant structures such as leaves and roots, as they do not need to photosynthesize or absorb water from soil. For example, the root holoparasite Rafflesia spp., which parasitize grape family trees, completely lack leaves and roots but have giant flowers (96,97). Similarly, Hydnora spp.-members of the Hydnoraceae, which have been referred to as "the strangest plants in the world"-obtain all of their nutrients from their host Euphorbiaceae species and lack leaf and photosynthetic activities (93).…”

Two hAT transposon genes were transferred from Brassicaceae to broomrapes and are actively expressed in some recipients

“…Parasite/host plant systems, which all involve distantly related species, are prone to HGT, because of the tight physical connections in the haustoria, which in the case of endoparasites, such as Rafflesia and Pilostyles , involve a network of parenchyma cells living inside the host 42 43 . DNA fragments are therefore transported between parasites and hosts and occasionally become integrated into parasite genomes ( Introduction ), with end-joining, homologous recombination, and virus-mediated integration as possible mechanisms 1 3 4 .…”

The Times They Are A-Changin’: Heterochrony in Plant Development and Evolution

“…The apomictic development of Boechera ovules has been associated with heterochronic gene expression patterns compared to non-apomictic (sexual) ovules ( Sharbel et al, 2010 ). The development of Rafflesiaceae, a holoparasitic plant family which infects grapevines, shows two heterochronic shifts: an arrest at the proembryonic stage, which can be considered an example of neoteny, and acceleration of the transition from the undifferentiated endophyte to flowering, skipping vegetative shoot maturation ( Nikolov et al, 2014 ).…”