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Progress in the Molecular Mechanism of the Parallel Loss of Petals


Progress in the Molecular Mechanism of the Parallel Loss of Petals Inquiry

Petals are an important medium for angiosperms to attract pollinators, showing diversity in morphology and structure. Studies have shown that petals evolved independently from bracts or stamens, but lost in different branches, leading to the independent origin of multiple petalless groups. However, so far, the molecular mechanism that causes the parallel loss of petals and the independent origin of the petalless groups is still unclear.

 

The Hongzhi Kong Research Group of the Institute of Botany, Chinese Academy of Sciences has long been engaged in the study of the molecular mechanisms of the origin and diversification of flowers and floral organs. Previous studies have found that the nearest common ancestor of Ranunculaceae plants has petals, but a petalless group evolved independently in nine branches; the “non-expression” of the petal identity gene APETALA3-3 (AP3-3) is closely related to the loss of petals, although the mechanism leading to its “non-expression” is not the same in different branches. However, due to limited sampling, the expression of the AP3-3 gene in other petalless branches of Ranunculaceae and its relationship with the loss of petals in parallel is not clear.

 

 

Recently, the research team used all nine representative species without petal branches as materials to systematically explore the molecular mechanism of the parallel loss of petals in Ranunculaceae through transcriptome, molecular evolution, comparative morphological, and functional studies. The study found that the non-expression or down-regulation of AP3-3 is indeed closely related to the complete loss of petals; among the nine petalless branches, AP3-3 may have been completely lost in the genus Hydrastis, Thalictrum, and Marsh marigold (Caltha). It exists in Enemion and Calathodes but does not express. In the three branches of Beesia and Clematis (Clematis) and Glaucidium are present and expressed, but the expression level is significantly reduced. It is normally expressed in Trautvetteria. Compared with the close relatives with petals, the number of sepals in wild petalless species often does not increase, but the number of stamens is relatively increased, indicating that the loss of petals is caused by the homologous conversion of petals to stamens; in a newly originated petalless group of Pseudomonas, the homologous conversion of petals to stamens may be the same as that of C The mutation in the regulatory region of functional gene AGAMOUS1 (AG1) and the resulting increase in the expression are related to the expansion of the expression range. These findings indicate that the loss of petals in most of the petalless branches of Ranunculaceae may be caused by the expansion of AG1 expression, and the loss, silence, and down-regulation of AP3-3 may be the result. This research is helpful to comprehensively understand the molecular mechanism of the parallel loss of petals in Ranunculaceae, and provides new ideas for understanding the problem of petal loss in other groups of angiosperms.

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