This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have recently reconstructed the ancestral karyotype of the banana family, revealing how chromosome numbers decreased stepwise from 17 to 9–11 over evolutionary time. The study was led by scientists from the South China Botanical Garden (SCBG) of the Chinese Academy of Sciences (CAS), in collaboration with researchers from Sichuan University and other institutions.
Their findings are published in Current Biology. The banana family (Musaceae) comprises approximately 80 extant species, with substantial diversity in chromosome base numbers (n = 11, 10 and 9) and bract color—a bract is a specialized leaf associated with a flower or inflorescence. Among the family, the best-known member is undoubtedly the cultivated banana (Musa spp.).
It provides a food source for more than 400 million people and is one of the most important economic crops in tropical and subtropical regions. However, modern cultivated varieties rely heavily on vegetative propagation, resulting in a narrow genetic base and low genetic diversity that make them particularly vulnerable to devastating diseases. To overcome these challenges, researchers need to turn to wild relatives of cultivated bananas to explore the untapped potential in their chromosome structure, genetic variation and adaptive traits.
In this study, researchers first generated a high-quality, telomere-to-telomere (T2T), gap-free genome assembly of Musa exotica, an early-diverging ornamental banana species, with a contig N50 of 47.41 Mb. By integrating this genome assembly with available Musaceae genomes, the researchers conducted comprehensive comparative genomic analyses and reconstructed the ancestral Musaceae karyotype (AMK), inferring an ancestral haploid chromosome number of n = 17. "A high-quality T2T genome is an important foundation of this study.
The genome provides a reliable reference for comparing chromosome structures among Musaceae species and supports subsequent ancestral karyotype reconstruction and comparative analyses," said Huang Huirun from SCBG, the co-corresponding author. According to the researchers, the ancestral karyotype reconstruction further revealed a stepwise reduction in chromosome number during Musaceae evolution. "The reconstructed ancestral karyotype provides an objective basis for comparing chromosome structures among Musaceae species and inferring their evolutionary trajectories.
It also offers a reference for further understanding the genetic information retained by wild relatives and its potential value for utilization," said Fu Ning from SCBG, the co-first author. The researchers found that the extant n = 11, n = 10 and n = 9 chromosome complements did not arise independently but evolved progressively from the ancestral n = 17 karyotype through multiple chromosome rearrangements, including reciprocal chromosome translocation (RCT), end-to-end joining (EEJ) and nested chromosome fusion (NCF). This evolutionary trajectory was highly consistent with DNA-based phylogenetic relationships, providing new independent evidence from chromosome structure for understanding the evolutionary relationships among major Musaceae lineages.
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