International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.6, 286-293 http://ecoevopublisher.com/index.php/ijmec 290 Figure 1 Floral organs of pineapple and floral diagrams of pineapple, rice, and the ancestral monocot (Adopted from Hu et al., 2021) Image caption: (A) Inflorescence of pineapple. Dense pineapple flowers are arranged in a spiral at the periphery of the spadix rachis. Each flower comprises sepals, petals, stamens, and pistils and is protected by one thick bract. (B) Floral diagrams of pineapple, rice, and the proposed ancestral monocot. Individual pineapple flowers are trimerous with three sepals (green) and petals (purple) in the two outer whorls, six stamens arranged in two whorls with three organs in each, and one pistil with three fused carpels in the center. In rice, there are two outer perianth organs (green, adaxial palea and abaxial lemma); two lodicules (red) internal to the lemma, corresponding to petals in non-grasses; six stamens in one whorl; and a single carpel. The floral structure of the ancestral monocot is similar to that of pineapple, except for the two outer whorls of perianth organs. Se sepal, pe petal, sta stamen, pa palea, le lemma, lo lodicule, ca carpel (Adopted from Hu et al., 2021) Their research also shows that although pineapple is related to other monocots like rice and banana—plants that went through many WGD events - it doesn’t have signs of recent duplications. This supports the idea that pineapple’s chromosome number and shape stayed mostly the same for a very long time. 6.4 Coordinated evolution via chromosomal rearrangement and functional conservation Even though pineapple didn’t duplicate genes often, its MADS-box genes still work very well. For example, genes like AcAG (C-class), AcAGL11a–c (D-class), AcSEP1/3 (E-class), and AcAGL6 show strong and flower-specific activity in all floral parts (see Figure 8C, page 10). This matches an old and steady flower development pattern. So instead of growing gene families through WGD, pineapple used changes in chromosome structure to keep its old gene network working. This helped keep its flower traits similar to those of early monocots, making pineapple a good plant for studying how flowers evolved in early angiosperms. 6.5 Conclusion and implications Pineapple followed a “low duplication, high stability” strategy in its genome. Without many duplication events or big jumps in gene numbers, it managed to keep its genome steady by changing chromosome structure instead. This makes pineapple a great model for studying early monocot flower evolution. It also gives helpful ideas for building stable genome systems in today’s crop gene editing work. 7 Comparative Genomics and Evolutionary Insights 7.1 Comparative genomics of pineapple, maize, and other monocots In the evolution of monocots, pineapple occupies a special position. It is often used as a model species for studying the evolution of Gramineae plants. Unlike corn, which uses C₄ photosynthesis, pineapple uses CAM (crassulacean acid metabolism) photosynthesis, and this key feature has become one of the highlights of its genome research (Ming et al., 2016).
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