Abstract
In the plant kingdom, the flower is one of the most relevant evolutionary novelties. Floral symmetry has evolved multiple times from the ancestral condition of radial to bilateral symmetry. During evolution, several transcription factors have been recruited by the different developmental pathways in relation to the increase of plant complexity. The MYB proteins are among the most ancient plant transcription factor families and are implicated in different metabolic and developmental processes. In the model plant Antirrhinum majus, three MYB transcription factors (DIVARICATA, DRIF, and RADIALIS) have a pivotal function in the establishment of floral dorsoventral asymmetry. Here, we present an updated report of the role of the DIV, DRIF, and RAD transcription factors in both eudicots and monocots, pointing out their functional changes during plant evolution. In addition, we discuss the molecular models of the establishment of flower symmetry in different flowering plants.
Highlights
The success of flowering plants is strictly related to the evolutionary innovations enclosed in the flower, whose ancestral form can be dated back ≈ 140–250 million years ago (Mya) [1,2,3,4]
Advances have been made in understanding the role of the MYB transcription factors (TFs) in the molecular network regulating flower symmetry
The MYB proteins DIV, DRIF, and RAD have assumed new functions, and the DDR regulatory module has been recruited for the establishment of flower symmetry
Summary
The success of flowering plants is strictly related to the evolutionary innovations enclosed in the flower, whose ancestral form can be dated back ≈ 140–250 million years ago (Mya) [1,2,3,4]. The MADS-box TFs are involved in a wide range of developmental pathways, from spore germination [14], gametophyte and sporophyte generation [14,15], the formation of motile flagella in sperms of non-seed plants [16], to root development [17,18,19], abiotic stress responses [20], tuber dormancy [21], and fruit expansion [22] They have been recruited in the pathway that drives the determination of flower organs, as explained by the canonical ABCDE model (mainly in eudicots) and its modifications (e.g., the fading borders in basal angiosperms, magnoliids, and basal eudicots, and the orchid code model in orchids) [23,24,25,26,27,28]
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