Abstract Detail

Molecular Ecology and Evolution

Steele, Kelly [1], Wojciechowski, Martin [2].

ndh gene loss from the plastid genome of the saguaro, Carnegiea gigantea (Cactaceae).

Eleven plastid-encoded ndh proteins along with many nuclear-encoded subunits constitute the NADH dehydrogenase-like complex (NDH) found in the thylakoid membrane of most land plant plastids. However, in certain groups of land plants some or all of the plastid-encoded ndh genes have been lost, particularly in hemi and holoparasitic plants (e.g., Orobanche) as well as mycoheterotrophic species (e.g., Monotropa uniflora), and some carnivorous plants (e.g., Genlisea aurea). This loss has been primarily attributed to relaxed selection on genes coding for proteins involved in photosynthesis. However, there are a few apparently fully autotrophic terrestrial groups such as Pinaceae, Gnetales, and a subclade of the genus Erodium, where the plastid-encoded ndh genes have been lost to varying degrees. This has been hypothesized to be due to transfer of the plastid-encoded ndh genes to the nuclear genome, dispensability of NDH under some environmental conditions or is considered to be inexplicable. An assembly of the plastid genome of saguaro cactus (Carnegiea gigantea) (Sanderson et al. in prep.; see poster at this meeting) contains only portions of the plastid-encoded ndhB and ndhD genes with no evidence of the remaining nine genes. Nuclear genome scaffolds from a preliminary whole genome assembly from saguaro do not include any open, full-length ndh genes, nor does it show the presence of functional nuclear-encoded genes for other subunits of NDH. Current research on cyclic electron flow (CEF) that occurs in land plant plastids has demonstrated its importance in photosynthesis and indicates the presence of two partially redundant pathways, one that utilizes NDH and another that utilizes the nuclear-encoded PGR5 and PGRL1 proteins. Genes for one of these latter two proteins are found in saguaro nuclear genome scaffolds supporting the hypothesis that this CEF pathway is found in the saguaro. Interestingly, genes for both those proteins are found in the recently published Lophophora williamsii (Cactaceae) transcriptome and are also found in the loblolly pine genome. No other taxa that lack plastid-encoded ndh genes have publically available whole genome sequence data, so the presence of those two genes in their genomes cannot be determined definitively. Our current hypothesis is that in some species, e.g., the saguaro, the presence of one of the two partially redundant pathways for CEF makes survival of autotrophic species that lack the plastid-encoded ndh genes possible.

1 - Arizona State University Polytechnic, College of Letters and Sciences, 6073 S. Backus Mall, Mesa, AZ, 85212, USA
2 - Arizona State University, School of Life Sciences, Tempe, AZ, 85287-4501, USA

Keywords:
plastid genome
saguaro
ndh
cyclic electron flow.

Presentation Type: Poster:Posters for Topics
Session: P
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Number: PME006
Abstract ID:1325
Candidate for Awards:None