BACKGROUND The morphological diversity of flower organs is closely related to functional divergence within the MADS-box gene family. Bryophytes and seedless vascular plants have MADS-box genes but do not have ABCDE or AGAMOUS-LIKE6 (AGL6) genes. ABCDE and AGL6 genes belong to the subgroup of MADS-box genes. Previous works suggest that the B gene was the first ABCDE and AGL6 genes to emerge in plant but there are no mentions about the probable origin time of ACDE and AGL6 genes. Here, we collected ABCDE and AGL6 gene 381 protein sequences and 361 coding sequences from gymnosperms and angiosperms and reconstructed a complete Bayesian phylogeny of these genes. In this study, we want to clarify the probable origin time of ABCDE and AGL6 genes is a great help for understanding the role of the formation of the flower, which can decipher the forming order of MADS-box genes in the future. RESULTS These genes appeared to have been under purifying selection and their evolutionary rates are not significantly different from each other. Using the Bayesian evolutionary analysis by sampling trees (BEAST) tool, we estimated that: the mutation rate of the ABCDE and AGL6 genes was 2.617 × 10-3 substitutions/site/million years, and that B genes originated 339 million years ago (MYA), CD genes originated 322 MYA, and A genes shared the most recent common ancestor with E/AGL6 296 MYA, respectively. CONCLUSIONS The phylogeny of ABCDE and AGL6 genes subfamilies differed. The APETALA1 (AP1 or A gene) subfamily clustered into one group. The APETALA3/PISTILLATA (AP3/PI or B genes) subfamily clustered into two groups: the AP3 and PI clades. The AGAMOUS/SHATTERPROOF/SEEDSTICK (AG/SHP/STK or CD genes) subfamily clustered into a single group. The SEPALLATA (SEP or E gene) subfamily in angiosperms clustered into two groups: the SEP1/2/4 and SEP3 clades. The AGL6 subfamily clustered into a single group. Moreover, ABCDE and AGL6 genes appeared in the following order: AP3/PI → AG/SHP/STK → AGL6/SEP/AP1. In this study, we collected candidate sequences from gymnosperms and angiosperms. This study highlights important events in the evolutionary history of the ABCDE and AGL6 gene families and clarifies their evolutionary path.

中文翻译：

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裸子植物和被子植物中 ABCDE 和 AGL6 亚家族 MADS-box 基因的起源和选择。

背景技术花器官的形态多样性与MADS-box基因家族的功能分化密切相关。苔藓植物和无籽维管植物具有 MADS-box 基因，但没有 ABCDE 或 AGAMOUS-LIKE6 (AGL6) 基因。ABCDE 和 AGL6 基因属于 MADS-box 基因亚组。之前的研究表明B基因是植物中最早出现的ABCDE和AGL6基因，但没有提及ACDE和AGL6基因的可能起源时间。在这里，我们收集了来自裸子植物和被子植物的ABCDE和AGL6基因的381个蛋白序列和361个编码序列，并重建了这些基因的完整贝叶斯系统发育。在本研究中，我们希望阐明ABCDE和AGL6基因的可能起源时间，对于理解花的形成的作用有很大帮助，从而可以破译未来MADS-box基因的形成顺序。结果这些基因似乎经过了纯化选择，它们的进化速度彼此之间没有显着差异。利用抽样树贝叶斯进化分析（BEAST）工具，我们估计：ABCDE和AGL6基因的突变率为2.617×10-3个替换/位点/百万年，B基因起源于3.39亿年前（MYA） ），CD基因起源于322 MYA，A基因分别与E/AGL6 296 MYA共享最近的共同祖先。结论 ABCDE 和 AGL6 基因亚家族的系统发育不同。APETALA1（AP1 或 A 基因）亚家族聚集为一组。APETALA3/PISTILLATA（AP3/PI 或 B 基因）亚家族分为两组：AP3 和 PI 进化枝。AGAMOUS/SHATTERPROOF/SEEDSTICK（AG/SHP/STK 或 CD 基因）亚家族聚集成一个组。被子植物中的 SEPALLATA（SEP 或 E 基因）亚家族分为两组：SEP1/2/4 和 SEP3 进化枝。AGL6 亚家族聚集成一个组。此外，ABCDE和AGL6基因按以下顺序出现：AP3/PI→AG/SHP/STK→AGL6/SEP/AP1。在这项研究中，我们收集了来自裸子植物和被子植物的候选序列。这项研究重点介绍了ABCDE和AGL6基因家族进化史上的重要事件，并阐明了它们的进化路径。