Shrub genome reveals secrets of flower power

Sangtee Kim

The plant Amborella is found natively only in New Caledonia.

A shrub with cream-coloured flowers that is the closest living descendant of Earths first flowering plants has had its genome decoded. The sequence of Amborella trichopoda hints at the genetic adaptations that helped flowers to emerge and conquer the world some 160 million years ago an evolutionary explosion described by Charles Darwin as an abominable mystery.

Nearly everything about Amborella is fodder for a botanists pub quiz. It grows natively in 18 known spots on the New Caledonian island of Grande Terre in the South Pacific, and nowhere else on Earth. The plants reproductive structures are encased in tepals a hybrid between petals and leaf-like support structures called sepals.

Amborella is the only species in its genus, family and order. Phylogenetically, its really the equivalent of the duck-billed platypus and monotremes, says Claude dePamphilis, a plant evolutionary biologist at Pennsylvania State University in University Park, who co-led researchers on the Amborella Genome Project. The fruits of their labour are published in three papers in Science today13.

Just as the platypus genome yielded insights into the emergence of mammals, Amborellas gives a glimpse at changes that helped flowering plants, or angiosperms, to diversify from a common ancestor with gymnosperms another major plant lineage, which includes conifer trees such as spruces.

Comparisons of the genomes of Amborella and those of other plants suggest that an early ancestor of flowering plants gained a duplicate copy of its genome, a feature known as polyploidy. Many angiosperms are known to be polyploid potatoes, for instance, have between two and six copies of each chromosome. But the duplication in Amborella predates all the other polyploids, says dePamphilis, who led a team in 2011 that inferred this ancient duplication from more limited genetic data4.

The duplication may have spurred the diversification and expansion of flowering plants by providing an extra copy of each gene for evolution to play around with to yield new functions, dePamphilis suggests.

The origin of flowers the defining features of angiosperms might be explained by a collection of genes that appeared when angiosperms split from gymnosperms, analysis of the Amborella genome reveals. About one-quarter of the genes involved in flowering lack obvious counterparts in the genomes of gymnosperms, whereas the other three-quarters existed in the common ancestor of both plant lineages. His teams analysis also provides insight into the evolution of complex seeds, floral scents and other features of flowering plants.

Keith Adams, a plant molecular geneticist at the University of British Columbia in Vancouver, Canada, thinks the idea that a genome duplication helped flowering plants to diversify is an intriguing hypothesis although its impossible to prove. Botanists studying other plants should find the Amborella genome useful as a reference point to identify and study families of genes in other plants, including crops, he says.

Read the original post:
Shrub genome reveals secrets of flower power