Abstract
BackgroundThe 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.ResultsThese 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.ConclusionsThe 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.
Highlights
The morphological diversity of flower organs is closely related to functional divergence within the MADS-box gene family
Identification of 381 ABCDE and AGL6 genes To examine the evolutionary history of ABCDE and AGL6 genes, we retrieved 381 sequences (Fig. 1, Table 1, Additional files 1, 2) from databases using known ABCDE and AGL6 protein sequences from A. thaliana and rice (O. sativa) as well as tomato MADS-box gene 6 (TM6) of S. lycopersicum as query sequences [2, 4, 6, 12, 29, 38, 41, 42] (Additional files 1, 2) in a Basic Local Alignment Search Tool (BLAST) search [43]
(2) An ancient duplication may have generated the ancestral (Ba) AP3 and PI lineages, and the AP3 lineage was lost in gymnosperms after a subsequent duplication
Summary
The morphological diversity of flower organs is closely related to functional divergence within the MADS-box gene family. 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. The MIKC-type TFs form two main groups: the MIKC* and the MIKCC type [12] After these genes emerged, flowering plants diversified substantially during the Cretaceous period to become the largest plant group on earth [7]. Their remarkable evolutionary success was primarily due to the newly evolved reproductive structures and is similar to the success of gymnosperms which use seeds as a new propagation system [13]. The appearance of MIKCC-type genes seems to be closely associated with the successful evolution of flowering plants
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