Ancient polyploidization predating divergence of the cereals

28-Aug-2020 03:05

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At least 32% of the species sampled are the result of genetic allopolyploidy and result from 28 distinct tetraploidy events plus an additional six hexaploidy events. Genetic allopolyploidy was documented using the characteristic pattern of double-labeled gene trees. Alternatively, allopolyploidy could correlate with diversification of a major clade or even the entire tribe (the diversification hypothesis), in which case most allopolyploids would be the product of a single polyploidy event followed by radiation at the tetraploid or hexaploid level; we would see only a handful of polyploidization events deep in the tree (Fig. Previous attempts to resolve relationships within Andropogoneae, using both chloroplast and nuclear markers, have produced phylogenies that are poorly supported, with intergeneric relationships unresolved (30–36). We therefore sought to test whether each allopolyploidy event leads only to one or a few species (the Stebbins hypothesis), in which case, the allopolyploids should appear in the phylogeny as the result of numerous independent polyploidy events. Studies of naturally occurring and synthetic polyploids find changes in gene expression, gene loss, release of transposons, and changes in morphology and physiology immediately after polyploidy (4, 8–12). Good mechanistic reasons support such a hypothesis.

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Here, we focus on the tribe Andropogoneae (subfamily Panicoideae), a group of about 1,200 species in 90 genera.

The parental genomes of most Andropogoneae polyploids diverged in the Late Miocene coincident with the expansion of the major CPolyploidy (whole-genome duplication) is often linked with the acquisition of new traits and subsequent species diversification, particularly in plants (1, 2).

This number is a minimum, and the actual frequency could be considerably higher.

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10% of the species of the clade, based on sequences of four concatenated low-copy nuclear loci.