Plants with double genomes might have had a better chance to survive the Cretaceous–Tertiary extinction event

Most flowering plants have been shown to be ancient polyploids that have undergone one or more whole genome duplications early in their evolution. Furthermore, many different plant lineages seem to have experienced an additional, more recent genome duplication. Starting from paralogous genes lying in duplicated segments or identified in large expressed sequence tag collections, we dated these youngest duplication events through penalized likelihood phylogenetic tree inference. We show that a majority of these independent genome duplications are clustered in time and seem to coincide with the Cretaceous–Tertiary (KT) boundary. The KT extinction event is the most recent mass extinction caused by one or more catastrophic events such as a massive asteroid impact and/or increased volcanic activity. These events are believed to have generated global wildfires and dust clouds that cut off sunlight during long periods of time resulting in the extinction of ≈60% of plant species, as well as a majority of animals, including dinosaurs. Recent studies suggest that polyploid species can have a higher adaptability and increased tolerance to different environmental conditions. We propose that polyploidization may have contributed to the survival and propagation of several plant lineages during or following the KT extinction event. Due to advantages such as altered gene expression leading to hybrid vigor and an increased set of genes and alleles available for selection, polyploid plants might have been better able to adapt to the drastically changed environment 65 million years ago.

Keywords:

• angiosperms
• eudicots
• Cretaceous–Tertiary boundary
• penalized likelihood
• polyploidy

comments on this papers as follow:

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

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 …

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