Legume Genomics and Genetics 2025, Vol.16, No.5, 204-214 http://cropscipublisher.com/index.php/lgg 204 Research Insight Open Access Expansin Gene Family in Legumes: Structural Diversity and Expression Dynamics Dandan Huang Hainan Institute of Biotechnology, Haikou, 570206, Hainan, China Corresponding email: dandan.huang@hibio.org Legume Genomics and Genetics, 2025 Vol.16, No.5 doi: 10.5376/lgg.2025.16.0021 Received: 03 Jul., 2025 Accepted: 20 Aug., 2025 Published: 05 Sep., 2025 Copyright © 2025 Huang, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Huang D.D., 2025, Expansin gene family in legumes: structural diversity and expression dynamics, Legume Genomics and Genetics, 16(5): 204-214 (doi: 10.5376/lgg.2025.16.0021) Abstract Expansins are plant-specific proteins that play crucial roles in cell wall loosening and are essential for various developmental processes and stress responses. This study comprehensively analyzes the expansin gene family in legumes, focusing on its structural diversity, evolutionary patterns, expression dynamics, and functional relevance. We classify expansins into α-expansin, β-expansin, and expansin-like A and B subfamilies and discuss their gene duplication events, chromosomal localization, and conserved domain structures in major legume species. Phylogenetic relationships and Ka/Ks ratio analyses provide new insights into their evolutionary trajectories and selective pressures. Furthermore, we investigate tissue-specific and developmental stage-specific expression patterns, highlighting the roles of expansins in root growth, nodulation, and pod formation. Expression profiles under various abiotic and biotic stress conditions reveal their involvement in stress adaptation mediated by hormone signaling pathways. Functional studies involving gene overexpression, gene knockout, and omics-based analyses highlight their contributions to cell expansion, stress tolerance, and the regulation of root system architecture. A case study focusing on soybean illustrates how differential expression and transgenic validation of expansin genes influence drought resistance and nodulation. This study lays the foundation for understanding the functions of expansin genes in legumes and provides prospects for their application in molecular breeding, genome editing, and improving stress tolerance in legume crops. Keywords Expansin proteins; Legumes; Gene expression dynamics; Evolutionary analysis; Stress response 1 Introduction In the growth regulation of plant cell walls, a type of substance called blotin has long been regarded as a key player. They do not break the components of the cell wall through hydrolysis, but rather help the cell wall extend in a specific way under acidic conditions by breaking non-covalent bonds. This type of protein is not just one or two, but A superfamily consisting of four subclasses: α -butenin (EXPA), β -butenin (EXPB), butenin-like A (EXLA), and butenin-like B (EXLB). Among them, EXPA and EXPB are the most active, especially in the aspect of loosening the cell wall. They are not only involved in seed germination or pollen tube growth, but also in leaf morphology, root bud elongation, flower and fruit development, and even the process of plant shedding. But the role of expansion protein is not limited to growth. When plants are subjected to abiotic stresses such as drought, saline-alkali conditions or abnormal temperatures, they are also "showing up". Furthermore, when symbiosis with microorganisms (such as mycorrhizae and rhizobia), these proteins also play a role in communication and adaptation (Cosgrove, 2015; Mohanty et al., 2017). Especially in leguminous plants, the expression of the expansin gene is of particular concern. They are involved in many important links related to adaptation and development, such as the adjustment of cell walls, which directly affects the structure of root systems and the formation of root nodules-and root nodules are closely related to nitrogen fixation. The expression of these genes is usually tissue-specific and can flexibly adjust according to external conditions such as drought, salt content changes, and even nutritional status. Take soybeans and alfalfa as examples. The expression of their tumescent protein genes in different tissues varies significantly, and they are also upregulated when subjected to osmotic pressure or salt stress. This indicates that they do not play a passive role in stress responses. During the symbiotic process with rhizobia, they also regulate the related mechanisms of root infection and root nodule development, and this regulation is often influenced by hormone levels and environmental signals (Giordano and Hirsch, 2004; Li et al., 2014).
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