Surviving the K-T mass extinction: New perspectives of polyploidization in angiosperms

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Abstract
Although it has long been recognized that polyploidy (now often referred to as genome doubling) has played a major role in angiosperm evolution (1), analyses of genomic data have dramatically increased interest in the function of polyploidy in shaping plant genome structure and diversity (e.g., reviewed in refs. 2–5). Whereas early estimates largely based on chromosome counts suggested that perhaps 30–50% of all angiosperms may be polyploids, modern genome studies prompted the stunning realization that all or nearly all angiosperms likely have polyploidy in their evolutionary history (e.g., ref. 6). For example, analyses of the small Arabidopsis genome, the putative “ideal” diploid, revealed 2 or 3 rounds of genomewide duplication (7, 8), and an estimated 59% of the duplicated genes over the last 350 million years are the result of whole genome duplications (WGDs) (9). There is also evidence of ancient WGD events in basal angiosperm lineages, near the origin of the eudicots, and in numerous other lineages including Vitis, Carica, and Populus (reviewed in ref. 10). This evidence for the pervasive influence of polyploidy throughout plant evolutionary history raises new questions about the evolutionary consequences of polyploidy in plants and has prompted a dramatic resurgence in the view of polyploidy as a major evolutionary force. In this issue of PNAS, Fawcett et al. (11) propose that genome doubling helped numerous plant lineages survive the Cretaceous-Tertiary (K-T) mass extinction. This intriguing hypothesis illustrates the modern polyploidy paradigm, which attributes enormous genomic versatility and concomitant evolutionary success to polyploid lineages (4). Using a novel method to date ancient genome duplications, Fawcett et al. estimated that ancient polyploidy events occurred at the same time (≈65 Mya) in several diverse angiosperm lineages, suggesting the possibility of a shared common causal factor. Interestingly, this estimate corresponds with the K-T …