Abstract
BackgroundSome plants develop a breeding system that produces both chasmogamous (CH) and cleistogamous (CL) flowers. However, the underlying molecular mechanism remains elusive.ResultsIn the present study, we observed that Viola philippica develops CH flowers with short daylight, whereas an extended photoperiod induces the formation of intermediate CL and CL flowers. In response to long daylight, the respective number and size of petals and stamens was lower and smaller than those of normally developed CH flowers, and a minimum of 14-h light induced complete CL flowers that had no petals but developed two stamens of reduced fertility. The floral ABC model indicates that B-class MADS-box genes largely influence the development of the affected two-whorl floral organs; therefore, we focused on characterizing these genes in V. philippica to understand this particular developmental transition. Three such genes were isolated and respectively designated as VpTM6-1, VpTM6-2, and VpPI. These were differentially expressed during floral development (particularly in petals and stamens) and the highest level of expression was observed in CH flowers; significantly low levels were detected in intermediate CL flowers, and the lowest level in CL flowers. The observed variations in the levels of expression after floral induction and organogenesis apparently occurred in response to variations in photoperiod.ConclusionsTherefore, inhibition of the development of petals and stamens might be due to the downregulation of B-class MADS-box gene expression by long daylight, thereby inducing the generation of CL flowers. Our work contributes to the understanding of the adaptive evolutionary formation of dimorphic flowers in plants.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0832-2) contains supplementary material, which is available to authorized users.
Highlights
Some plants develop a breeding system that produces both chasmogamous (CH) and cleistogamous (CL) flowers
We revealed the variations in the development of petals and stamens, which are the major affected floral organs in the formation of dimorphic flowers in V. philippica under different photoperiods
Because the growth and differentiation of both petals and stamens were to some extent inhibited in the CHinCL-CL floral transition in V. philippica with extended photoperiods, we investigated the role of B-class MADS-box genes in the development of these twowhorl floral organs
Summary
Some plants develop a breeding system that produces both chasmogamous (CH) and cleistogamous (CL) flowers. Flowers are typically composed of four organ types: sepals, petals, stamens, and carpels, which run from the outside of the flower to the center. The ABC model of flower development explains how three major function class genes (A-, B-, and C-class) specify the identity of the four floral organ types. A-class alone controls sepals, A-class in combination with B-class controls petals, Bclass in combination with C-class controls stamens, and C-class alone controls carpels [1, 2]. Mutations in either the AP3/DEF or PI/ GLO genes results in similar phenotypic variations, wherein petals are transformed into sepals, and stamens into carpels [7,8,9]. The B-class lineages apparently underwent duplications and subsequent functional divergence in some core eudicots, possibly playing a role in
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