CHASE, MARK W.1*, ANTONY V. COX1, SANDY KNAPP2, JEFFREY JOSEPHS1, and ALEX S. PAROKONNY3,4. 1Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3DS, UK; 2The Natural History Museum, London SW7 5BD, UK; 3Institute of Cell Biology and Genetics, Kiev, Ukraine; 4Nottingham University, Nottingham, UK.. - Molecular systematics, GISH, and the origin of amphidiploids in Nicotiana (Solanaceae).
Phylogenetic relationships in the genus Nicotianawere
investigated using parsimony analyses of the internal transcribed
spacer (ITS) regions of nuclear ribosomal DNA (nrDNA) and compared to
previously published results from the plastid matKgene. In
addition, origins of amphidiploid taxa in Nicotianawere
investigated using the techniques of genomic in situ hybridization
(GISH). All taxa regardless of ploidy produced clean single copies of
the ITS region, even though some taxa are natural hybrids and others
are artificial hybrids (allopolyploids). The patterns of relationships
in Nicotianaare largely congruent with previous evolutionary
ideas of Goodspeed, who studied their morphology and cytology, but
some important differences are apparent. None of the subgenera of
Nicotianais monophyletic, and although most of the currently
recognized sections are coherent, others are clearly polyphyletic.
Relying solely upon ITS nrDNA and matKanalysis to reveal
phylogenetic patterns in a complex genus such as Nicotianais
insufficient, and it is clear that conventional analysis of single
data sets, such as ITS, is likely to be misleading in at least some
respects about evolutionary history. ITS sequences of artificial as
well as natural and well-documented amphidiploids are similar to one
of their two parents, usually the maternal (but not always) and not in
any sense themselves "hybrid". Knowing how ITS evolves in
artificial amphidiploids gives insight into what the ITS analysis
might reveal about naturally occurring amphidiploids for which little
of their origin is known, and it is in this perspective that analysis
of ITS sequences is highly informative.
Key words: amphidiploids, GISH, hybridization, ITS, matK, Nicotiana