Scientists peel back ancient layers of banana DNA to reveal ‘mystery ancestors’

Frontiers in Plant Science (2022). DOI: 10.3389/fpls.2022.969220″ width=”800″ height=”530″/>

Map of the island of New Guinea and examples of fruits of M. acuminata ssp. banksii. Credit: Frontiers in plant sciences (2022). DOI: 10.3389/fpls.2022.969220

Bananas are thought to have been first domesticated on the island of New Guinea 7,000 years ago. But the domestication history of bananas is complicated, with their classification hotly debated, as the boundaries between species and subspecies are often unclear.

Now, a study in Frontiers in plant sciences shows that this history is even more complex than previously thought. The results confirm that the genome of current domestic breeds contains traces of three additional, as yet unknown, ancestors.

“Here we show that most of the current diploid cultivated bananas that are descended from the wild banana M. acuminata are hybrids between different subspecies. At least three additional wild ‘mysterious ancestors’ must have contributed to this mixed genome thousands of years ago, but have not yet been identified,” said Dr. Julie Sardos, a scientist at The Alliance of Bioversity International and CIAT in Montpellier, France, and the first author of the study.

Complex domestication history

Domesticated bananas (except for the Pacific Fei bananas) are said to have descended from a cluster of four ancestors – or subspecies of the wild banana Musa acuminataor different but closely related species. M. acuminata appears to have evolved in the northern borderland between India and Myanmar, having existed in Australasia for about 10 million years before being first domesticated. Another complication is that domesticated varieties can have two (“diploid”), three (“triploid”) or four (“tetraploid”) copies of each chromosome, and many are also descended from the wild species. M. balbisiana.

Recent studies on a smaller scale suggested that even this already complex scenario may not be the whole story, and further ancestors related to mr. insight may have been involved in domestication. The new results not only confirm that this is indeed the case, they also show for the first time that these gene pools are common in domestic banana genomes.

Banana Collecting Missions

The authors sequenced the DNA in 226 leaf extracts from the world’s largest collection of banana samples at The Alliance of Bioversity International and CIAT’s “Musa Germplasm Transit Center” in Belgium. Of these samples, 68 to nine belonged to wild subspecies of M. acuminata154 to diploid domestic varieties descended from M. acuminata, and four more distantly related wild species and hybrids for comparison. Many had previously gathered on special ‘banana-collecting missions’ to Indonesia, the island of New Guinea and the Autonomous Region of Bougainville.

The researchers first measured the relationship levels between cultivars and wild bananas and created “family trees” based on the diversity of 39,031 Single Nucleotide Polymorphisms (SNPs). They used a subset of these — evenly distributed across the genome, with each pair delineating a block of about 100,000 “DNA letters” — to statistically analyze the ancestry of each block. For the first time, they found traces of three other ancestors in the genome of all domestic samples, with no known similarities from the wild.

Mysterious ancestors can survive somewhere

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The mysterious ancestors may have been extinct long ago. “But our personal belief is that they still live somewhere in the wild, either poorly described by science or not described at all, in which case they are likely endangered,” Sardos said.

Sardos et al. have a good idea where to look: “Our genetic comparisons show that the first of these mysterious ancestors must have come from the region between the Gulf of Thailand and west of the South China Sea. The second, from the region between North Borneo and the Philippines. The third, from the island of New Guinea.”

Can help grow better bananas

What useful properties these mysterious ancestors may have contributed to domesticated bananas is not yet known. For example, the crucial property of parthenocarpy, fruit set without the need for pollination, is thought to be inherited from M. acuminata

while cooking bananas owes much of their DNA to the subspecies (or perhaps separate species) M. acuminata banksii.

Second corresponding author Dr. Mathieu Rouard, also at Bioversity International, said: “Identifying the ancestors of cultivated bananas is important as it will help us understand the processes and pathways that have shaped today’s banana diversity, a critical step to growing bananas from the future.”

“Breeders need to understand the genetic makeup of current domesticated diploid bananas for their crosses between cultivars, and this study is an important first step towards the detailed characterization of many of these cultivars.”

Sardos said: “Based on these results, we will work with partners to explore and genotyping the diversity of wild bananas across the three geographic regions identified by our study, hoping to identify these unidentified contributors to cultivated bananas. It will also be important to explore the different benefits and properties that each of these contributors gave to cultivated bananas.”

Hunting for wild bananas in Papua New Guinea

More information:
Julie Sardos et al, Hybridization, missing wild ancestors and the domestication of cultivated diploid bananas, Frontiers in plant sciences (2022). DOI: 10.3389/fpls.2022.969220

Quote: Scientists peel off ancient layers of banana DNA to reveal ‘mysterious ancestors’ (2022, October 7), retrieved October 7, 2022 from -dna. html

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