Pumpkin genomes sequenced, revealing unusual evolutionary historical past


Pumpkin species from world wide. Credit score: Zhangjun Fei and Marissa Zuckerman

For some, pumpkins conjure carved Halloween decorations, however for many individuals world wide, these gourds present diet. Scientists at Boyce Thompson Institute (BTI) and the Nationwide Engineering Analysis Heart for Greens in Beijing have sequenced the genomes of two necessary pumpkin species, Cucurbita maxima and Cucurbita moschata.

The completed genomes seem within the October problem of Molecular Plant, which highlights the work on its cowl.

“Pumpkins are used as a staple meals in lots of growing international locations and are cultivated everywhere in the world for his or her culinary and decorative makes use of,” stated Zhangjun Fei, affiliate professor at BTI, Cornell adjunct affiliate professor of plant pathology and a senior creator of the paper. Over two-thirds of the world’s pumpkins, squash and gourds are produced in Asia alone.

The researchers sequenced the 2 completely different pumpkin species to higher perceive their contrasting fascinating traits: Cucurbita moschata is understood for its resistance to illness and different stresses, resembling excessive temperatures, whereas C. maxima is best identified for its fruit high quality and diet.

Moreover, the hybrid of those two species, referred to as ‘Shintosa’ has even better stress tolerance than C. moschata, and is usually used as a rootstock for different cucurbit crops, resembling watermelon, cucumber, and melon. Growers will minimize the pumpkin seedling from its roots, and fuse the stems of different cucurbits onto it, giving them robust, resistant roots to develop from.

This graph reveals the manufacturing of pumpkins, squash and gourds: Prime ten producers in 2014. Credit score: FAOSTAT

As soon as deciphered, the genome sequences are an necessary useful resource for additional scientific badysis and breeding of Cucurbita crops. By badyzing the genomes, researchers will be capable to establish many genes related to the pumpkin’s fascinating traits, and higher perceive the genetics behind the intense phenotypes of the ‘Shintosa’ hybrid.

“The high-quality pumpkin genome sequences will result in extra environment friendly dissection of the genetics underlying necessary agronomic traits, thus accelerating the breeding course of for pumpkin enchancment,” stated Fei.

Within the cucurbit world, this implies quicker breeding for resistance to ailments resembling fusarium wilt or powdery mildew – that white movie many gardeners would possibly discover killing their squash leaves, or enhancing manufacturing of carotenoids – the orange pigments related to eye well being, amongst different advantages.

Whereas the last word objective for genome sequencing is to have the ability to hyperlink particular genes to the traits they management, the pumpkin sequencing outcomes additionally revealed an attention-grabbing evolutionary historical past for Cucurbita species.

Cucurbitas have mbadive genomes with 20 pairs of chromosomes, in comparison with watermelon’s 11 or cucumber’s 7. This was the primary clue that the pumpkin’s genome had expanded a very long time in the past. By evaluating the Curcurbita genome sequences to these of different cucurbits, the researchers found that the pumpkin genome is definitely a mix of two historical genomes, making it a paleotetraploid.

Pumpkin carved with DNA double helix. Credit score: Alexa M. Schmitz

Though the pumpkin is taken into account a diploid in the present day, which means that it has solely two copies of every chromosome, the genome sequence evaluation revealed that between Three-20 million years in the past, two completely different ancestral species mixed their genomes to create an allotetraploid – a brand new species with 4 (tetra-) copies of every chromosome, from two completely different (allo-) species.

Sometimes after an allotetraploid is fashioned, the genome will expertise downsizing and gene loss, ultimately reworking the brand new species again right into a diploid. Typically, one of many contributing genomes will dominate over the others to retain extra genes, a phenomenon noticed in maize and cotton.

Curiously, for pumpkins this was not the case. The traditional Cucurbita allotetraploid misplaced its duplicated genes randomly from each of the contributing diploids. Moreover, the ancestral chromosome remained largely intact, leaving the fashionable pumpkin with two subgenomes representing the traditional species that contributed to the paleotetraploid.

“We have been excited to search out out that the present two subgenomes in pumpkin largely preserve the chromosome buildings of the 2 progenitors regardless of sharing the identical nucleus for at the least three million years,” stated Shan Wu, first creator of the paper and BTI postdoc.

The following time you carve a pumpkin, take a second to consider the curious evolutionary path it took to get right here, and the way breeders, now armed with the genome sequence, will likely be higher in a position to enhance the pumpkin to badist feed hundreds of thousands world wide.

Discover additional:
Exploring an historical occasion in pumpkin, gourd and melon evolution

Extra info:
Honghe Solar et al, Karyotype Stability and Unbiased Fractionation within the Paleo-Allotetraploid Cucurbita Genomes, Molecular Plant (2017). DOI: 10.1016/j.molp.2017.09.003

Journal reference:
Molecular Plant

Supplied by:
Boyce Thompson Institute

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