Abstract
ABSTRACTRapid putative radiations of Rheum might be caused by the recent uplifts of the Qinghai–Tibetan Plateau and the quaternary climate oscillations. To better understand the molecular adaptation associated with Rheum radiation, in this study, the adaptive evolution of the chloroplast rbcL gene was analysed using the Phylogenetic Analysis Program. The results showed that two amino acid residues (75F, 203I) were under positive selection. The spatial analysis indicated that the site (75F) was located in the β-sheet of the N-terminal loops involved in subunit interactions in the L8S8 molecule, and the site (203I) was in the α/β-barrel active centre located on the C-terminal domain of the large subunit of Rubisco. These results suggest that potential positive selection in rbcL might have played an important role in the adaption of Rheum species to the extreme environments in Qinghai–Tibetan Plateau regions, and different species lineages might have been subjected to different selective pressures.
Highlights
Rheum is one of the largest genera in the family Polygonaceae with about 60 species primarily distributed in mountainous and desert regions of the Qinghai–Tibetan Plateau and adjacent areas, and a few extending to or occurring in central/western Asia and Europe [1,2]
For example, has broad rigid leaves with a waxy surface and channels cut into them to collect rainwater, with enough power to cause deep soil penetration [8]. These changes in morphology and physiology may result from the adaptive evolution of some orthologous genes which code for functional proteins, such as the chloroplast ndhF and rbcL genes, which are related to photosynthesis and photorespiration [9]
Because only the catalytic region of the rbcL gene was taken into account, the clustering relationship was basically consistent with the geographical distribution within Rheum in the Maximum Parsimony (MP) tree, and all of the Rheum species comprised a well-supported lineage with a sister relationship to Oxyria
Summary
Rheum is one of the largest genera in the family Polygonaceae with about 60 species primarily distributed in mountainous and desert regions of the Qinghai–Tibetan Plateau and adjacent areas, and a few extending to or occurring in central/western Asia and Europe [1,2]. Some species have evolved into dwarf plants with coriaceous basal leaves or drooping bracts. For example, has broad rigid leaves with a waxy surface and channels cut into them to collect rainwater, with enough power to cause deep soil penetration [8]. These changes in morphology and physiology may result from the adaptive evolution of some orthologous genes which code for functional proteins, such as the chloroplast ndhF and rbcL genes, which are related to photosynthesis and photorespiration [9]. The phylogenetic analysis suggested that positive selection in ndhF has likely played a major role in the adaptive evolution of Rheum species [10]
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