The scientists imagine there are at the very least three wild ‘mystery ancestors’.
Scientists are peeling again historic layers of banana DNA so as to discover the “mystery ancestors” earlier than they go extinct.
It is believed that people domesticated bananas for the primary time 7,000 years in the past on the island of New Guinea. However, the historical past of banana domestication is difficult, and the excellence between species and subspecies is commonly unclear.
A brand new research printed within the journal Frontiers in Plant Science reveals that this historical past is considerably extra difficult than beforehand imagined. The findings present that the genomes of the present domesticated varieties embrace remnants from three additional, as of but unidentified, ancestors.
“Here we show that most of today’s diploid cultivated bananas that descend from the wild banana M. acuminata are hybrids between different subspecies. At least three extra wild ‘mystery ancestors’ must have contributed to this mixed genome thousands of years ago, but haven’t been identified yet,” mentioned Dr. Julie Sardos, a scientist at The Alliance of Bioversity International and CIAT in Montpellier, France, and the research’s first creator.
Complex domestication historical past
Domesticated bananas (apart from Fei bananas within the Pacific) are believed to have descended from a bunch of 4 ancestors, which have been both subspecies of the wild banana Musa acuminata or totally different however carefully associated species. Before being domesticated, M. acuminata existed in Australasia and appears to have developed on the northern borderlands between India and Myanmar about 10 million years in the past. Another complication is that domesticated varieties might include two (‘diploid’), three (‘triploid’), or 4 (‘tetraploid’) copies of each chromosome, and lots of are derived from the wild species M. balbisiana.
Recent smaller-scale research urged that different ancestors linked to M. acuminata might have been concerned within the domestication, suggesting that even this extremely difficult situation is probably not the entire story. The newest findings not solely validate this to be the case but additionally display for the primary time that these gene swimming pools are widespread in domesticated banana genomes.
Banana amassing missions
The authors sequenced the DNA in 226 extracts leaf extracts from the world’s largest collection of banana samples at The Alliance of Bioversity International and CIAT’s “Musa Germplasm Transit Centre” in Belgium. Among these samples, 68 belonged to nine wild subspecies of M. acuminata, 154 to diploid domesticated varieties descended from M. acuminata, and four more distantly related wild species and hybrids as comparisons. Many had previously been gathered in dedicated ‘banana collecting missions’ to Indonesia, the island of New Guinea, and the autonomous region of Bougainville.
The researchers first measured the levels of relatedness between cultivars and wild bananas and made “family trees” based on the diversity at 39,031 Single Nucleotide Polymorphisms (SNPs). They used a subset of these – evenly spread across the genome, with each pair demarcating a block of approximately 100,000 “DNA letters” – to statistically analyze the ancestry of each block. For the first time, they detected traces of three further ancestors in the genome of all domesticated samples, for which no matches are yet known from the wild.
Mystery ancestors might survive somewhere
The mystery ancestors might be long since extinct. “But our personal conviction is that they are still living somewhere in the wild, either poorly described by science or not described at all, in which case they are probably threatened,” said Sardos.
Sardos and his team have a good idea of where to look for them: “Our genetic comparisons show that the first of these mystery ancestors must have come from the region between the Gulf of Thailand and west of the South China Sea. The second is from the region between north Borneo and the Philippines. The third, from the island of New Guinea.”
Could help breed better bananas
Which useful traits these mystery ancestors might have contributed to domesticated bananas is not yet known. For example, the crucial trait of parthenocarpy, fruit setting without the need for pollination, is thought to have been inherited from M. acuminata, while cooking bananas owe a large chunk of their DNA to the subspecies (or perhaps separate species) M. acuminata banksii.
Second corresponding author Dr. Mathieu Rouard, likewise at Bioversity International, said: “Identifying the ancestors of cultivated bananas is important, as it will help us understand the processes and the paths that shaped the banana diversity observed today, a crucial step to breed bananas of the future.”
“Breeders need to understand the genetic make-up of today’s domesticated diploid bananas for their crosses between cultivars, and this study is a major first step toward the characterization in great detail of many of these cultivars.”
Sardos said: “Based on these results, we will work with partners to explore and genotype wild banana diversity in the three geographic regions that our study pinpointed, with the hope to identify these unidentified contributors to cultivated bananas. It will also be important to investigate the different advantages and traits that each of these contributors provided to cultivated bananas.”
Reference: “Hybridization, missing wild ancestors and the domestication of cultivated diploid bananas” by Julie Sardos, Catherine Breton, Xavier Perrier, Ines Van den Houwe, Sebastien Carpentier, Janet Paofa, Mathieu Rouard and Nicolas Roux, 7 October 2022, Frontiers in Plant Science.
DOI: 10.3389/fpls.2022.969220
The study was funded by the CGIAR Research Program Roots, Tubers and Bananas, and the CGIAR Genebank Platform.
