BackgroundThe most frequent case of horizontal transfer in plants involves a group I intron in the mitochondrial gene cox1, which has been acquired via some 80 separate plant-to-plant transfer events among 833 diverse angiosperms examined. This homing intron encodes an endonuclease thought to promote the intron's promiscuous behavior. A promising experimental approach to study endonuclease activity and intron transmission involves somatic cell hybridization, which in plants leads to mitochondrial fusion and genome recombination. However, the cox1 intron has not yet been found in the ideal group for plant somatic genetics - the Solanaceae. We therefore undertook an extensive survey of this family to find members with the intron and to learn more about the evolutionary history of this exceptionally mobile genetic element.ResultsAlthough 409 of the 426 species of Solanaceae examined lack the cox1 intron, it is uniformly present in three phylogenetically disjunct clades. Despite strong overall incongruence of cox1 intron phylogeny with angiosperm phylogeny, two of these clades possess nearly identical intron sequences and are monophyletic in intron phylogeny. These two clades, and possibly the third also, contain a co-conversion tract (CCT) downstream of the intron that is extended relative to all previously recognized CCTs in angiosperm cox1. Re-examination of all published cox1 genes uncovered additional cases of extended co-conversion and identified a rare case of putative intron loss, accompanied by full retention of the CCT.ConclusionsWe infer that the cox1 intron was separately and recently acquired by at least three different lineages of Solanaceae. The striking identity of the intron and CCT from two of these lineages suggests that one of these three intron captures may have occurred by a within-family transfer event. This is consistent with previous evidence that horizontal transfer in plants is biased towards phylogenetically local events. The discovery of extended co-conversion suggests that other cox1 conversions may be longer than realized but obscured by the exceptional conservation of plant mitochondrial sequences. Our findings provide further support for the rampant-transfer model of cox1 intron evolution and recommend the Solanaceae as a model system for the experimental analysis of cox1 intron transfer in plants.

The tribe Hyoscyameae (Solanaceae) is restricted to Eurasia and includes the genera Archihyoscyamus, Anisodus, Atropa, Atropanthe, Hyoscyamus, Physochlaina, Przewalskia and Scopolia. Even though the monophyly of Hyoscyameae is strongly supported, the relationships of the taxa within the tribe remain unclear. Chloroplast markers have been widely used to elucidate plant relationships at low taxonomic levels. Identification of variable chloroplast intergenic regions has been developed based on comparative genomics of chloroplast genomes, but these regions have a narrow phylogenetic utility. In this study, we present the chloroplast genome sequence of Hyoscyamus niger and make comparisons to other solanaceous plastid genomes in terms of gene order, gene and intron content, editing sites, origins of replication, repeats, and hypothetical open reading frames. We developed and sequenced three variable plastid markers from eight species to elucidate relationships within the tribe Hyoscyameae. The presence of a horizontally transferred intron in the mitochondrial cox1 gene of some species of the tribe is considered here a likely synapomorphy uniting five genera of the Hyoscyameae. Alternatively, the cox1 intron could be a homoplasious character acquired twice within the tribe. A homoplasious inversion in the intergenic plastid spacer trnC-psbM was recognized as a source of bias and removed from the data set used in the phylogenetic analyses. Almost 12 kb of plastid sequence data were not sufficient to completely resolve relationships among genera of Hyoscyameae but some clades were identified. Two alternative hypotheses of the evolution of the genera within the tribe are proposed.

In this paper we explore how changes in human strategies are differentially modulated by climate in a border area between hunter-gatherers and farmers. We analyze multiple proxies: radiocarbon summed probability distributions (SPDs), stable C and N isotopes, and zooarchaeological data from northwestern Patagonia. Based on these proxies, we discuss aspects of human population, subsistence, and dietary dynamics in relation to long-term climatic trends marked by variation in the Southern Annular Mode (SAM). Our results indicate that the farming frontier in northwestern Patagonia was dynamic in both time and space. We show how changes in temperature and precipitation over the last 1000 years cal BP have influenced the use of domestic plants and the hunting of highest-ranked wild animals, whereas no significant changes in human population size occurred. During the SAM positive phase between 900 and 550 years cal BP, warmer and drier summers are associated with an increase in C4 resource consumption (maize). After 550 years cal BP, when the SAM changes to the negative phase, wetter and cooler summer conditions are related to a change in diet focused on wild resources, especially meat. Over the past 1000 years, there was a non-significant change in the population based on the SPD.

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Short repeats (SR) play an important role in shaping seed plant mitochondrial genomes (mtDNAs). However, their origin, distribution, and relationships across the different plant lineages remain unresolved. We focus on the angiosperm family Solanaceae that shows a wide diversity in repeat content and extend the study to a wide diversity of seed plants. We determined the complete nucleotide sequences of the organellar genomes of the medicinal plant Physochlaina orientalis (Solanaceae), member of the tribe Hyoscyameae. To understand the evolution of the P. orientalis mtDNA we made comparisons with those of five other Solanaceae. P. orientalis mtDNA presents the largest mitogenome (~685 kb in size) among the Solanaceae and has an unprecedented 8-copy repeat family of ~8.2 kb in length and a great number of SR arranged in tandem-like structures. We found that the SR in the Solanaceae share a common origin, but these only expanded in members of the tribe Hyoscyameae. We discuss a mechanism that could explain SR formation and expansion in P. orientalis and Hyoscyamus niger. Finally, the great increase in plant mitochondrial data allowed us to systematically extend our repeat analysis to a total of 136 seed plants to characterize and analyze for the first time families of SR among seed plant mtDNAs.

The southern boundary of prehispanic farming in South America occurs in central Mendoza Province, Argentina at approximately 34 degrees south latitude. Archaeological evidence of farming includes the recovery of macrobotanical remains of cultigens and isotopic chemistry of human bone. Since the 1990s, archaeologists have also hypothesized that the llama (Lama glama), a domesticated South American camelid, was also herded near the southern boundary of prehispanic farming. The remains of a wild congeneric camelid, the guanaco (Lama guanicoe), however, are common in archaeological sites throughout Mendoza Province. It is difficult to distinguish bones of the domestic llama from wild guanaco in terms of osteological morphology, and therefore, claims that llama were in geographic areas where guanaco were also present based on osteometric analysis alone remain equivocal. A recent study, for example, claimed that twenty-five percent of the camelid remains from the high elevation Andes site of Laguna del Diamante S4 were identified based on osteometric evidence as domestic llama, but guanaco are also a likely candidate since the two species overlap in size. We test the hypothesis that domesticated camelids occurred in prehispanic, southern Mendoza through analysis of ancient DNA. We generated whole mitochondrial genome datasets from 41 samples from southern Mendoza late Holocene archaeological sites, located between 450 and 3400 meters above sea level (masl). All camelid samples from those sites were identified as guanaco; thus, we have no evidence to support the hypothesis that the domestic llama occurred in prehispanic southern Mendoza.

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In this paper we evaluate the role of human strategies in the Andean Piedmont from northern Patagonia across the Holocene. Specifically, we present the analysis of the Early Holocene-Late Holocene archaeological record of Salamanca cave (Mendoza-Argentina). We identified technological changes that occurred during the Late Holocene and the implications of a human occupation hiatus in the Middle Holocene. We follow a multiproxy approach by the analysis of radiocarbon dates, archaeofaunal remains, ceramic, lithics and XRF obsidian sourcing. We also discuss a detailed stratigraphic sequence by geomorphological descriptions, the construction of a radiocarbon sequence model and summed probability distributions, compared with other archaeological sites in the region. We conclude that after the Middle Holocene archaeological hiatus, human populations grew while guanaco populations dropped. The imbalance between demography and resources boosted the incorporation of new technologies such as ceramics and the bow and arrow, allowing people to exploit lower-ranked resources.