Legume Genomics and Genetics 2025, Vol.16, No.3, 128-134 http://cropscipublisher.com/index.php/lgg 130 2016; Zhang et al., 2016). Most of these differences are due to the fact that species face different types of pathogens, and the directions of their evolutionary choices are naturally different as well. 3.3 Gene family expansion, duplication events, and selection pressure analysis Ultimately, why are there so many genes like NS-LRR? In fact, the expansion mode is quite clear. Most of them are achieved through tandem replication or fragment repetition, and over time, a bunch of gene clusters are formed (Liu et al., 2025). More interestingly, genes of the CNL class often expand gradually, while TNL shrinks in some lineages (Zhang et al., 2016). Some studies have pointed out that these changes are closely related to past genome-wide repeat events, especially during the period from the Cretaceous to the Paleogene, which might be the node of the massive explosion of the NS-LRR gene (Shao et al., 2016). Coupled with the continuous pressure from pathogens, these gene families have become increasingly diverse and "specialized" in terms of immune function. 4 Gene Structure and Conserved Motif Analysis 4.1 Comparative Analysis of exon–intron Structures If one examines the structure of NS-LRR genes in leguminous plants, especially in close relatives of red beans like common kidney beans and soybeans, it is not difficult to notice a characteristic - the structural types are highly inconsistent. Some genes have a considerable number of exons and introns, but there are exceptions. Simple structures also exist (Kang et al., 2012; Wu et al., 2017). Among them, the TNL type usually has several more exons and a slightly longer intron length than the CNL type. Some people think that this might be related to their functional differentiation and the complication of regulatory mechanisms (Bezerra-Neto et al., 2020). However, such structural diversity actually indicates from another perspective that this type of genetic system might be a kind of "flexibility" evolved to cope with the constantly changing pathogenic environment. 4.2 Conserved amino acid sequences and functional motif identification When it comes to NS-LRR proteins, the key to their function in immunity lies in those several classic conserved motifs within them. In the NB-ARC region, sequences such as the P-ring, kinase 2, and GLPL are almost standard, used to assist in binding and hydrolyzing ATP or GTP (Bezerra-Neto et al., 2020). Although the LRR region varies greatly, the recurring leucine-rich motif remains the core part as it is responsible for interacting with other proteins or recognizing pathogens (Bezerra-Neto et al., 2020). Also, don't forget the N-terminal domain, TIR or CC. Different types of genes also have differences here, corresponding to different functional characteristics and signaling pathways (Wu et al., 2017). So although there are many types of sequences, those conservative segments are basically the basis for maintaining the immune function of NS-LRR. 4.3 Structural variation and potential functional implications among genes Is there any significance in structural differences at all? From the current perspective, there indeed is. There are significant differences among NBS-LRR genes in exon-intron structure, the number of domains and even motif composition (Zhang et al., 2016; Bezerra-Neto et al., 2020). Behind these differences, events such as gene replication, recombination and motif rearrangement often play a role, which may generate some "new versions" of resistance genes, giving plants more room to deal with different pathogens. Interestingly, these changes are not only at the individual level; in many cases, they can also contribute to the formation of gene clusters, thereby enabling an entire set of related resistance traits to be regulated and co-evolve together. 5 Expression Patterns and Stress Response Characteristics 5.1 Expression profiles in different tissues and developmental stages Not all NS-LRR genes are expressed "actively" in plants. In kidney beans, some genes prefer to emerge at specific sites, such as roots, flowers, flower buds and young pods, while others either "quietly" maintain low expression levels or remain online throughout the year with little fluctuation (Wu et al., 2017). In fact, this situation is not uncommon among leguminous plants, and soybeans are no exception. This organizational specificity makes one have to consider that they may each undertake different "job responsibilities", some may be more inclined towards developmental control, while others are like "defensive posts" on standby at all times.
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