The Amborella vacuolar processing enzyme family

Abstract

Most vacuolar proteins are synthesized on rough endoplasmic reticulum as proprotein precursors and then transported to the vacuoles, where they are converted into their respective mature forms by vacuolar processing enzymes (VPEs). In the case of the seed storage proteins, this process is of major importance, as it conditions the establishment of vigorous seedlings. Toward the goal of identifying proteome signatures that could be associated with the origin and early diversification of angiosperms, we previously characterized the 11S-legumin-type seed storage proteins from Amborella trichopoda, a rainforest shrub endemic to New Caledonia that is also the probable sister to all other angiosperms (Amborella Genome Project, 2013). In the present study, proteomic and genomic approaches were used to characterize the VPE family in this species. Three genes were found to encode VPEs in the Amborella's genome. Phylogenetic analyses showed that the Amborella sequences grouped within two major clades of angiosperm VPEs, indicating that the duplication that generated the ancestors of these clades occurred before the most recent common ancestor of living angiosperms. A further important duplication within the VPE family appears to have occurred in common ancestor of the core eudicots, while many more recent duplications have also occurred in specific taxa, including both Arabidopsis thaliana and Amborella. An analysis of natural genetic variation for each of the three Amborella VPE genes revealed the absence of selective forces acting on intronic and exonic single-nucleotide polymorphisms among several natural Amborella populations in New Caledonia.

A Combination of Histological, Physiological, and Proteomic Approaches Shed Light on Seed Desiccation Tolerance of the Basal Angiosperm Amborella trichopoda

“…A drop of sterile Milli-Q water was placed on the endospermic face on each half. Embryos were quickly extracted (in <1 min), with extra-thin needles and immediately frozen in liquid nitrogen [ 13 ].…”

“…Fleshy parts of drupes were removed to obtain seeds. Seeds of a given batch were from the same shrub; they were all scarified by soaking them in a solution of sulfuric acid for 20 min and then rinsed several times with water [ 13 , 27 ]. Seed batches were desiccated by equilibration for one week at 25 °C using different saturated salt solutions [ 28 ] The nine saturated salt solutions, namely KOH, C 2 H 3 KO 2 , MgCl 2 , K 2 CO 3 , NH 4 NO 3 , NaCl, (NH 4 ) 2 SO 4 , KCl, and KNO 3 , allowed to obtain a range of nine different relative humidities (RHs), with values of 9%, 23%, 34%, 45%, 62%, 75%, 81%, 85%, 92%, respectively.…”

“…It is a dioecious shrub, 2–6 m high, which is endemic to New Caledonia and grows at medium altitude (400–800 m) in wet forests. Several studies have been carried out on this species to reveal plesiomorphic (primitive) characters, notably concerning its vegetative anatomy [ 7 ], its fruits [ 8 , 9 , 10 , 11 ], the very special structure of its vascular system that does not possess xylemic vessels [ 12 ], or the evolution of gene families [ 6 , 13 ].…”

Two disjunct Pleistocene populations and anisotropic postglacial expansion shaped the current genetic structure of the relict plant Amborella trichopoda

“…Amborella trichopoda is an emblematic understory shrub and a relevant model species to assess the biogeography of New Caledonian rainforests [ 15 ]. Furthermore, Amborella is the most basal clade of angiosperms, and previous studies have investigated its genome and genetic diversity in order to understand the evolution of flowering plants [ 21 – 25 ]. Recent microsatellite marker studies [ 13 , 26 ] revealed well-differentiated and geographically distinct genetic groups.…”

The morphophysiological dormancy inAmborella trichopodaseeds is a pleisiomorphic trait in angiosperms

“…Secondly, our findings contribute to a growing picture of the ecophysiology of A. trichopoda within its endemic habitat of the New Caledonian rain forest. We thus add data on seed dormancy and germination to studies of photosynthesis (Feild et al, 2001), stomatal function (Rudall and Knowles, 2013), vascular function (Feild et al, 2000;Turgeon and Medville, 2011;Feild and Wilson, 2012), flowering time (Fourcade et al, 2015), pollination biology (Thien et al, 2009), seed physiology (Poncet et al, 2015), population structure (Thien et al, 2003;Poncet et al, 2013) and genetic diversity (Poncet et al, 2012). These diverse studies of A. trichopoda make a major contribution to the concerted reconstruction of the ecophysiological features of the first flowering plants (see Feild et al, 2004;Feild and Arens, 2007).…”