Abstract
The Zingiberales is an order of tropical monocots that exhibits diverse floral morphologies. The evolution of petaloid, laminar stamens, staminodes, and styles contributes to this diversity. The laminar style is a derived trait in the family Cannaceae and plays an important role in pollination as its surface is used for secondary pollen presentation. Previous work in the Zingiberales has implicated YABBY2-like genes, which function in promoting laminar outgrowth, in the evolution of stamen morphology. Here, we investigate the evolution and expression of Zingiberales YABBY2-like genes in order to understand the evolution of the laminar style in Canna. Phylogenetic analyses show that multiple duplication events have occurred in this gene lineage prior to the diversification of the Zingiberales. Reverse transcription-PCR in Canna, Costus, and Musa reveals differential expression across floral organs, taxa, and gene copies, and a role for YABBY2-like genes in the evolution of the laminar style is proposed. Selection tests indicate that almost all sites in conserved domains are under purifying selection, consistent with their functional relevance, and a motif unique to monocot YABBY2-like genes is identified. These results contribute to our understanding of the molecular mechanisms underlying the evolution of floral morphologies.
Highlights
IntroductionLaminar outgrowth is a key process in the development of lateral organs, facilitating light capture and gas exchange (leaves), pollinator attraction (petals and sometimes other floral organs), and protection of the floral bud (sepals and bracts)
Laminar outgrowth is a key process in the development of lateral organs, facilitating light capture and gas exchange, pollinator attraction, and protection of the floral bud
We obtained sequences for YABBY2-like genes from representative taxa across the Zingiberales in order to investigate the evolution of this gene subfamily and its potential role in the evolution of floral morphology in this order, the evolution of laminarity in the gynoecium
Summary
Laminar outgrowth is a key process in the development of lateral organs, facilitating light capture and gas exchange (leaves), pollinator attraction (petals and sometimes other floral organs), and protection of the floral bud (sepals and bracts). The YABBY gene family was believed to be specific to seed plants, but YABBY genes have been found in the green alga Micromonas pusilla (Worden et al, 2009). Since these genes have not been found in any other non-seed plants, it is unclear when this gene family evolved in plants. Members of this family encode transcription factors characterized by two domains, a zinc finger domain at the N terminus and a YABBY domain at the C terminus (Bowman and Smyth, 1999; Sawa et al, 1999a). Four gene duplication events in this gene family have occurred prior to the diversification of the angiosperms (Bartholmes et al, 2012), leading to genes with both novel and redundant functions
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