Legume Genomics and Genetics 2025, Vol.16, No.5, 204-214 http://cropscipublisher.com/index.php/lgg 206 various plants. Although in legumes and other angiosperms, most of the bulking protein genes belonging to the same subfamily can cluster into one category, showing a certain degree of conservation, the boundaries between subfamilies remain quite distinct. That is to say, they look like a family on the outside, but in fact, they have been working separately for a long time. Comparative studies have shown that the number and distribution of genes in various species are not exactly the same, but the core subfamily structure remains constant, indicating that conservation and diversity are two coexisting aspects in the process of plant evolution (Li et al., 2002; Sun et al., 2021). Figure 1 Amino acid phylogenetic tree of wild soybean expansin family members (Adopted from Feng et al., 2022) 3.2 Role of gene duplication events (segmental, tandem) in the evolution of the expansin family When it comes to why the expansin gene family has become so large, it is impossible to avoid an old acquaintance-gene replication. Fragment replication and tandem replication almost constitute the main theme of the expansion of the expansin gene. This is particularly evident in the research of soybeans: nearly 70% of the expansin genes are formed through fragment replication, and tandem replication also contributes nearly 15%. Although they differ in proportion, both play a key role in "creating" diversity. Interestingly, these replications do
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