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Introgression can produce novel genetic variation in organisms that hybridize. Sympatric species pairs in the carnivorous plant genusSarraceniaL. frequently hybridize, and all known hybrids are fertile. Despite being a desirable system for studying the evolutionary consequences of hybridization, the extent to which introgression occurs in the genus is limited to a few species in only two field sites. Previous phylogenomic analysis ofSarraceniaestimated a highly resolved species tree from 199 nuclear genes, but revealed a plastid genome that is highly discordant with the species tree. Such cytonuclear discordance could be caused by chloroplast introgression (i.e. chloroplast capture) or incomplete lineage sorting (ILS). To better understand the extent to which introgression is occurring inSarracenia, the chloroplast capture and ILS hypotheses were formally evaluated. Plastomes were assembledde-novofrom sequencing reads generated from 17 individuals in addition to reads obtained from the previous study. Assemblies of 14 whole plastomes were generated and annotated, and the remaining fragmented assemblies were scaffolded to these whole-plastome assemblies. Coding sequence from 79 homologous genes were aligned and concatenated for maximum-likelihood phylogeny estimation. The plastome tree is extremely discordant with the published species tree. Plastome trees were simulated under the coalescent and tree distance from the species tree was calculated to generate a null distribution of discordance that is expected under ILS alone. A t-test rejected the null hypothesis that ILS could cause the level of discordance seen in the plastome tree, suggesting that chloroplast capture must be invoked to explain the discordance. Due to the extreme level of discordance in the plastome tree, it is likely that chloroplast capture has been common in the evolutionary history ofSarracenia.
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A procedure to introduce point mutations into the Rubisco large subunit gene in wild‐type plants
SUMMARY Photosynthetic inefficiencies limit the productivity and sustainability of crop production and the resilience of agriculture to future societal and environmental challenges. Rubisco is a key target for improvement as it plays a central role in carbon fixation during photosynthesis and is remarkably inefficient. Introduction of mutations to the chloroplast‐encoded Rubisco large subunitrbcL is of particular interest for improving the catalytic activity and efficiency of the enzyme. However, manipulation ofrbcL is hampered by its location in the plastome, with many species recalcitrant to plastome transformation, and by the plastid's efficient repair system, which can prevent effective maintenance of mutations introduced with homologous recombination. Here we present a system where the introduction of a number of silent mutations intorbcL within the model plantNicotiana tabacumfacilitates simplified screening via additional restriction enzyme sites. This system was used to successfully generate a range of transplastomic lines from wild‐typeN. tabacumwith stable point mutations withinrbcL in 40% of the transformants, allowing assessment of the effect of these mutations on Rubisco assembly and activity. With further optimization the approach offers a viable way forward for mutagenic testing of Rubisco functionin plantawithin tobacco and modification ofrbcL in other crops where chloroplast transformation is feasible. The transformation strategy could also be applied to introduce point mutations in other chloroplast‐encoded genes.
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- Award ID(s):
- 1642386
- PAR ID:
- 10453705
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- The Plant Journal
- Volume:
- 106
- Issue:
- 3
- ISSN:
- 0960-7412
- Page Range / eLocation ID:
- p. 876-887
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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