International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 286-293 http://ecoevopublisher.com/index.php/ijmec 289 stress pathways. In the development of floral organs, the expression of MADS-box genes also shows tissue specificity - some duplicated genes are highly expressed in the floral part, indicating that they may be directly involved in the reproductive development process (Pan et al., 2022). These cases together show that gene duplication not only increases the amount of genetic material, but also brings "upgrade packages" at the functional level. 5.3 Evolutionary significance of tandem duplication and whole genome duplication In the genome evolution path of pineapple, tandem duplication and whole genome duplication (WGD) have left traces to varying degrees. But it is worth noting that pineapple has not experienced an ancient WGD event that grass plants have. Even so, it still achieved the expansion of multiple gene families through high-frequency tandem duplication. For example, the expansion of the FRS gene family is largely due to this mechanism (Yow et al., 2021). In addition, tandem duplication also plays a role in the development of floral organs and the formation of reproductive functions. It is worth emphasizing that the transition of pineapple from C₃ to CAM photosynthesis was not achieved by large-scale genome reconstruction, but through the evolution of multiple small and precise regulatory levels (Pan et al., 2022). The accumulation of these changes enables pineapple to adapt to different ecological environments and show strong survival and evolution capabilities. 6 Case Study: The Conserved Karyotype of Pineapple Reveals a Unique Evolutionary Path Involving Chromosomal Rearrangement Without Recent Whole-Genome Duplications 6.1 Background Although whole genome duplication (WGD) is generally considered to be an important mechanism for the expansion of plant gene function, pineapple (Ananas comosus) seems to have chosen another evolutionary path. Pineapples, orchids, and rice differ greatly in flower morphology. Pineapple is a perennial monocotyledonous plant in the Bromeliaceae family. Each pineapple flower consists of three broad ovate fleshy sepals in whorl 1, three oblong petals in whorl 2, six stamens in whorl 3, and one pistil in whorl 4 from the outside to the inside, with three fused carpels (Figure 1). Compared with other monocots such as rice and orchids, pineapple has not experienced recent WGD events, and its MADS-box gene family has fewer members and a more conservative structure. The stability of this gene family indicates that pineapple did not rely on large-scale genome duplication during evolution, but maintained the ancient chromosome framework through a series of specific chromosome structure rearrangements. This conservation provides us with a new perspective to understand how plants achieve diversification in a "non-replication" context, and also suggests that changes in chromosome microstructure also play an important role in plant evolution. 6.2 Conserved karyotype and absence of recent WGD Hu et al. (2021) finds that pineapple and rice both share an old WGD event that happened early in monocot history. But after they split, pineapple shows no sign of any new WGD events. In fact, only one pair of genes (AcFUL1 and AcFUL2) seems to come from that ancient duplication. Another pair (AcAGL11a and AcAGL11c) likely formed from a small duplication inside pineapple itself. Most of the other MADS-box genes in pineapple exist as single copies. This is very different from rice and orchids, which show large gene expansions. Pineapple also has only 43 MADS-box genes, and 32 of them are type II. That number is much lower than in orchids. This limited number of genes is closely tied to the stable structure of pineapple’s chromosomes. 6.3 Conserved seven-chromosome karyotype and evolutionary significance Hu et al. (2021) shows that pineapple’s ABCDE MADS-box genes are spread across seven chromosome groups. This means it kept a very stable chromosome structure, with no recent chromosome splits or fusions. In rice, however, similar genes are found on many more chromosomes.
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