Alliance Bioversity International - CIAT, Montpellier, France.
AGAP, Université de Montpellier, CIRAD, INRA, Montpellier SupAgro, Montpellier, France.
Ann Bot. 2021 Jan 1;127(1):7-20. doi: 10.1093/aob/mcaa032.
Bananas (Musa spp.) are a major staple food for hundreds of millions of people in developing countries. The cultivated varieties are seedless and parthenocarpic clones of which the ancestral origin remains to be clarified. The most important cultivars are triploids with an AAA, AAB or ABB genome constitution, with A and B genomes provided by M. acuminata and M. balbisiana, respectively. Previous studies suggested that inter-genome recombinations were relatively common in banana cultivars and that triploids were more likely to have passed through an intermediate hybrid. In this study, we investigated the chromosome structure within the ABB group, composed of starchy cooking bananas that play an important role in food security.
Using SNP markers called from RADSeq data, we studied the chromosome structure of 36 ABB genotypes spanning defined taxonomic subgroups. To complement our understanding, we searched for similar events within nine AB hybrid genotypes.
Recurrent homologous exchanges (HEs), i.e. chromatin exchanges between A and B subgenomes, were unravelled with at least nine founding events (HE patterns) at the origin of ABB bananas prior to clonal diversification. Two independent founding events were found for Pisang Awak genotypes. Two HE patterns, corresponding to genotypes Pelipita and Klue Teparod, show an over-representation of B genome contribution. Three HE patterns mainly found in Indian accessions shared some recombined regions and two additional patterns did not correspond to any known subgroups.
The discovery of the nine founding events allowed an investigation of the possible routes that led to the creation of the different subgroups, which resulted in new hypotheses. Based on our observations, we suggest different routes that gave rise to the current diversity in the ABB cultivars, routes involving primary AB hybrids, routes leading to shared HEs and routes leading to a B excess ratio. Genetic fluxes took place between M. acuminata and M. balbisiana, particularly in India, where these unbalanced AB hybrids and ABB allotriploids originated, and where cultivated M. balbisiana are abundant. The result of this study clarifies the classification of ABB cultivars, possibly leading to the revision of the classification of this subgroup.
香蕉（Musa spp.）是发展中国家数亿人的主要主食。栽培品种是无籽和单性结实的克隆体，其祖先起源仍不清楚。最重要的品种是三倍体，基因组构成为 AAA、AAB 或 ABB，A 和 B 基因组分别由 M. acuminata 和 M. balbisiana 提供。先前的研究表明，种间基因组重组在香蕉品种中较为常见，三倍体更有可能经历过中间杂种。在这项研究中，我们研究了由淀粉质烹饪香蕉组成的 ABB 组的染色体结构，这些香蕉在食品安全中起着重要作用。
使用 RADSeq 数据中称为 SNP 标记的方法，我们研究了跨越定义的分类亚组的 36 个 ABB 基因型的染色体结构。为了补充我们的理解，我们在九个 AB 杂种基因型中搜索了类似的事件。
重复的同源交换（HEs），即在 A 和 B 亚基因组之间发生的染色质交换，在 ABB 香蕉的克隆多样化之前，通过至少九个创始事件（HE 模式）揭示了其起源。在 Pisang Awak 基因型中发现了两个独立的创始事件。HE 模式 Pelipita 和 Klue Teparod 对应着 B 基因组贡献的过度表现。在印度品种中发现的三个 HE 模式共享一些重组区域，而另外两个模式与任何已知的亚组都不对应。
九个创始事件的发现允许对导致不同亚组形成的可能途径进行调查，从而提出了新的假设。基于我们的观察，我们提出了导致 ABB 品种当前多样性的不同途径，包括初级 AB 杂种途径、导致共享 HE 的途径和导致 B 过量比的途径。遗传流动发生在 M. acuminata 和 M. balbisiana 之间，特别是在印度，那里起源了不平衡的 AB 杂种和 ABB allotriploids，并且那里有丰富的栽培 M. balbisiana。这项研究的结果澄清了 ABB 品种的分类，可能导致该亚组的分类修订。
