Legume Genomics and Genetics 2024, Vol.15, No.4, 152-162 http://cropscipublisher.com/index.php/lgg 154 chromosomal evolution and gene conservation. For example, the genome of Medicago truncatula, a model legume, has been extensively studied to understand its syntenic relationships with other legumes. The improved genome assembly of M. truncatula cv. R108, which includes chromosome-length scaffolds, has enabled accurate synteny analysis and comprehensive genome-scale comparisons (Kaur et al., 2021). Additionally, the cytogenetic map of Vigna angularis was compared with those of Vigna unguiculata and Phaseolus vulgaris, revealing a high degree of macrosynteny and identifying specific chromosomal rearrangements that have occurred since their divergence (Martins et al., 2021). These comparative analyses highlight the evolutionary processes that have shaped the genomes of both model species and economically important legume crops. 3.3 Impact of synteny on gene conservation and divergence The conservation of syntenic blocks has a profound impact on gene conservation and divergence within the legume family. Synteny helps preserve the functional integrity of gene clusters, which is crucial for maintaining essential biological processes. For instance, the study of glutamine synthetase (GS) and phosphoenolpyruvate carboxylase (PEPC) gene families in narrow-leafed lupin demonstrated that whole genome duplications have largely retained the function of these gene duplicates, contributing to the diversity and adaptability of legumes (Czyż et al., 2020). Furthermore, the identification of conserved syntenic blocks containing RLK and RLP genes across multiple legume species suggests that these genes play a critical role in stress responses and have been conserved through evolutionary pressures (Restrepo-Montoya et al., 2021). However, synteny also allows for divergence through chromosomal rearrangements and gene duplications, which can lead to the development of new traits and increased genetic diversity. The study of the pea genome, for example, revealed intense gene dynamics and genomic rearrangements that have contributed to its evolution and adaptation (Kreplak et al., 2019). These findings illustrate the dual role of synteny in both conserving essential genes and facilitating evolutionary innovation within the legume family. 4 Chromosomal Evolution in Legumes 4.1 Historical perspectives on chromosomal changes in legumes The legume family, Fabaceae, has undergone significant chromosomal changes throughout its evolutionary history. Early studies have highlighted the role of whole-genome duplications, segmental duplications, and independent gene duplications or losses in shaping the genomes of various legume species (Ren et al., 2019). The genus Cercis, for instance, provides a model for an early evolutionary form of the legume genome, suggesting that the legume progenitor had seven chromosomes, which diversified into the various legume subfamilies (Stai et al., 2019). This early chromosomal configuration and subsequent duplications have been pivotal in the diversification and adaptation of legumes. 4.2 Significant chromosomal rearrangements and their functional implications Several case studies have provided insights into the significant chromosomal rearrangements in legumes and their functional implications. For example, the cytogenetic mapping of Vigna angularis, Vigna unguiculata, and Phaseolus vulgaris revealed multiple chromosomal rearrangements, including reciprocal translocations and inversions, which have occurred after the divergence of these species (Martins et al., 2021). These rearrangements are believed to be hotspots for chromosomal evolution and de novo centromere formation. In another study, the reference genome assembly for pea (Pisum sativum) highlighted intense gene dynamics and chromosomal rearrangements, which are associated with genome size expansion and the evolution of agronomically important traits (Kreplak et al., 2019). The orthology and synteny analysis of receptor-like kinases (RLK) and receptor-like proteins (RLP) in legumes further demonstrated the dynamic evolution of these genes, with a high proportion of RLK and RLP genes being conserved in syntenic blocks across different legume species (Restrepo-Montoya et al., 2021). For instance, the peanut genome illustrates significant chromosomal rearrangements, such as translocations between chromosomes A03 and B03, which highlight the functional implications of chromosomal evolution in legume species (Figure 1) (Zhuang et al., 2019).
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