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Tang L.,Key Laboratory of Horticulture for Southern Mountain Regions | Tang L.,Southwest University | Tang J.-M.,Chongqing University of Arts and Sciences | Tan S.,Key Laboratory of Horticulture for Southern Mountain Regions | And 7 more authors.
Nordic Journal of Botany | Year: 2015

The internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA) is one of the most used molecular characters in plant systematics. Our previous studies based on morphological analysis and ITS sequence variation suggested that Malus toringoides (Rehd.) Hughes is derived from hybridization between M. transitoria (Batal.) Schneid. and M. kansuensis (Batal.) Schneid. To further understand the variation pattern of ITS sequences in M. toringoides, and to elucidate the evolutionary processes that affect ITS sequence variation after hybridization, we sampled 99 accessions from multiple populations of the hybrid and parental species, and then obtained totally 254 ITS sequences by cloning and sequencing. Our ITS variation data demonstrates three outcomes of ITS repeats after hybrid speciation. ~ 27-41% of M. toringoides have only M. transitoria type ITS sequence, ~ 40-70% have M. transitoria type ITS sequence plus one or two chimeric ITS sequences generated by recombination between parental ITS sequences, and six accessions retain both parental type ITS sequences. The plausible evolutionary processes that created the observed ITS variations were inferred to be the joint actions of recombination, concerted evolution, pseudogenization and backcrossing. Our study provides further understandings of the variation model of ITS repeats after hybridization as well as the evolution of M. toringoides after its hybrid speciation. © 2013 The Authors.

Li X.,Southwest University | Li X.,Chinese Academy of Agricultural Sciences | Xie R.,Southwest University | Xie R.,Chinese Academy of Agricultural Sciences | And 5 more authors.
Journal of the American Society for Horticultural Science | Year: 2010

Citrus species are among the most important fruit trees in the world and have a long cultivation history. However, until now, the exact genetic origins of cultivated Citrus such as sweet orange (Citrus sinensis), lemon (C. limon), and grapefruit (C. paradisi) have remained unidentified. In the present study, amplified fragment length polymorphism (AFLP) fingerprints, nuclear internal transcribed spacer (ITS), and three plastid DNA regions (psbH - petB, trnL - trnF, and trnS - trnG) of 30 accessions of the cultivated citrus and their putative wild ancestors were analyzed in an attempt to identify their paternal and maternal origins. Molecular phylogenetic trees were constructed based on the AFLP data, and chloroplast DNA and ITS sequences using the genus Poncirus as the outgroup. Our results indicated that bergamot (C. aurantifolia) and lemon were derived from citron (C. medica) and sour orange (C. aurantium), and grapefruit was a hybrid that originated from across between pummelo (C. grandis) and sweet orange. Rough lemon (C. limon) was probable as a parent of rangpur lime (C. limonia) and guangxi local lemon (C. limonia). Our data also demonstrated that sweet orange and sour orange were hybrids of mandarin (C. reticulata) and pummelo, while rough lemon was a cross between citron and mandarin. For mexican lime (C. aurantifolia), our molecular data confirmed a species of Papeda to be the female parent and C. medica as the male. These findings provide new information for future study on the taxonomy, evolution, and genetic breeding of Citrus.

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