Extremes in chromosome numbers in closely related taxa: A combined approach to studying the underlying karyotype evolution

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A long-standing question about plant genomes is how some groups have managed to organize their gene content on tremendously varying numbers of chromosomes, sometimes over short evolutionary time spans. This is the question we propose to address here, using the Araceae genus Typhonium as a study system. Asian Typhonium have 2n = 10, Australian Typhonium can have 2n = 160, these being the lowest and almost highest numbers in the family. New and published counts also imply a broad range of base chromosome numbers in Typhonium. In a multi-locus phylogeny of Typhonium, the 2n = 10 species are embedded among species with higher chromosome numbers, implying chromosome loss or fusion, while the high counts imply multiple rounds of polyploidization. We propose to investigate (i) karyotype rearrangements that led to chromosome number reduction or multiplication; (ii) genome size changes accompanying chromosome number changes; and (iii) the evolutionary context of changes in genome size and/or chromosome number (for example, time and place, as estimated from the phylogeny). Techniques to be used are molecular phylogenetics, genome size measurements, and fluorescence in situ hybridization (FISH) with repetitive DNA sequences. Pilot FISH data, using material from our large collection of cultivated Typhonium, demonstrate the suitability of Typhonium as a system for genome evolution.