Legume Genomics and Genetics 2025, Vol.16, No.5, 204-214 http://cropscipublisher.com/index.php/lgg 207 not occur alone in one place. They often concentrate in specific regions on chromosomes and gradually form gene clusters. This local "clustering" not only enables these genes to be preserved but also provides opportunities for subsequent functional differentiation. Thus, the abilities to adapt to developmental needs and cope with environmental changes were gradually established (Li et al., 2024; Wang et al., 2024c). 3.3 Selective pressures and evolutionary rates inferred from Ka/Ks analyses Not all genes function freely during the process of evolution. In fact, most of the genes for bloating proteins are very "regular". From the analysis of the Ka/Ks ratio, it can be seen that for both soybeans and two-grain wheat, the majority of their tumescent protein gene pairs show a Ka/Ks ratio less than 1, indicating that they have undergone purification selection and tend to retain their original functions with few modifications. But this doesn't mean there are no changes at all. Positive selection signals may appear at certain specific loci, especially in regions related to functional differences. That is to say, these places seem more willing to "take risks" and try some new changes, especially within certain specific subfamilies. The existence of such positive selection actually indirectly indicates that the expansion protein genes are not static; they are still seeking opportunities to evolve new functional possibilities (Li et al., 2023). 4 Expression Dynamics during Plant Development 4.1 Tissue-specific expression patterns in roots, stems, leaves, flowers, and nodules Different tissues "speak" in different ways during development-each tissue has its own "language", that is, a specific combination of gene expressions. In parts such as roots, stems, leaves and flowers, different genes each take the stage and perform their own functions. In model plants like Arabidopsis thaliana, through transcriptome and proteome studies, it has been found that each tissue has its own unique expression profile, which varies greatly from one another. Take Gen for example, studies on single-cell transcriptomes have revealed significant differences in gene expression among different cell types, and these differences are constantly adjusted as the development stage progresses. But not all parts are as clear as the roots. For instance, in above-ground organs such as leaves and flowers, the changes in expression are more closely related to tissue maturity. The later it goes, the more regular the expression becomes (Jean-Baptiste et al., 2019). There are also tissues such as flowers and seeds, which belong to reproductive structures. Their expression changes are often related to organ identity confirmation and maturation rhythm (Wellmer et al., 2006). 4.2 Temporal regulation during key developmental stages Gene expression is not always so "free and unrestrained". At some critical junctures, such as when seeds just germinate, organs first form, or when entering the reproductive stage, the rhythm of expression becomes particularly tight and layered. During the early embryo and germination stages, many genes suddenly "come online", with changes in expression regions and times. This transcriptional recombination is actually setting the tone for cell fate and paving the way for subsequent differentiation (Palovaara et al., 2017). However, once it comes to the development period of the floral organs, the situation is quite different. Some specific gene families are only expressed when flower buds are formed or organs are initially established, and then they fall silent. And groups of co-expressed genes act like a baton, dominating the entire process from organ initiation to maturity (Ryan et al., 2015). The development process of the stem is similar, but with a slightly different rhythm. It usually goes through a series of stages from cell division to expansion and then to secondary growth, and the transcriptome expression also changes accordingly (Zhang et al., 2024). 4.3 Correlation of expansin expression with cell expansion and morphogenesis Regarding the expansion proteins in leguminous plants, we don't have much direct data at hand yet, but some studies on model plants have already revealed quite a few clues. Cell expansion is not something that can be accomplished by a single gene working alone; it requires the collaborative efforts of an entire "team": those that regulate cell wall relaxation, maintain turgor pressure, and respond to hormone signals will all be collectively upregulated at critical stages. For instance, during the rapid growth period of leaves, the expression levels of those genes related to the cell wall are often very high, especially those responsible for wall structure adjustment
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