ISHS Acta Horticulturae 706: IV International Symposium on Brassicas and XIV Crucifer Genetics Workshop
ANALYSIS OF THE 5S RDNA NOR-TRANSCRIBED SPACER REGION OF BRASSICA AND ALLIED GENERA |
| Authors: | V. Sabharwal, M.S. Negi, N. Wilson, M. Lakshmikumaran |
| Keywords: | 5S rDNA NTS, Brassica coenospecies, phylogenetic analysis |
| Abstract:
The phylogenetic relationship among the Brassica coenospecies was investigated using sequences of the non-transcribed spacer (NTS) of 5S rDNA. Intragenomic sequence similarities were high indicating that concerted evolution has almost completely homogenised the multiple copies of 5S rDNA repeats present in the nuclear genome. The tree of the aligned 5S NTS sequences was obtained using the Maximum Parsimony method of phylogenetic construction. In this tree Brassica coenospecies were divided into two distinct lineages, the Rapa/Oleracea and the Nigra lineage. The Rapa/Oleracea lineage comprised B. rapa, B. oleracea, D. erucoides and E. gallicum. The high levels of sequence similarity supported the view that D. erucoides is the closest ancestor of B. rapa and B. oleracea. The close association between E. gallicum and D. erucoides was explained by the fact that D. erucoides is one of the parents of the amphidiploid E. gallicum species. The Nigra lineage was biphyletic with B. nigra, S. arvensis, E. abyssinicum, B tournefortii, B. spinescens and D. siifolia forming one clade and the Sinapis species along with R. sativus forming the other. The status of E. abyssinicum has been a point of contention. The cpDNA RFLP studies have placed this species in the Rapa/Oleracea lineage while on the basis of species-specific nuclear repeats it has been placed in the Nigra lineage. The positioning of D. siifolia is congruent with the results of cpDNA RFLP studies; while the placement of R. sativus in the Nigra lineage is in contrast with the results of cpDNA studies, but is supported by previous studies based on 5S NTS and ITS rDNA regions. The 5S rDNA analysis placed S. aucheri in the Sinapis cluster of the Nigra lineage, a finding inconsistent with the results of previous studies based on cpDNA RFLP, but supported by the morphological data. | |
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