Abstract
BackgroundFlower development is central to angiosperm reproduction and is regulated by a broad range of endogenous and exogenous stimuli. It has been well documented that ambient temperature plays a key role in controlling flowering time; however, the mechanisms by which temperature regulates floral organ differentiation remain largely unknown.ResultsIn this study, we show that low temperature treatment significantly increases petal number in rose (Rosa hybrida) through the promotion of stamen petaloidy. Quantitative RT-PCR analysis revealed that the expression pattern of RhAG, a rose homolog of the Arabidopsis thaliana AGAMOUS C-function gene, is associated with low temperature regulated flower development. Silencing of RhAG mimicked the impact of low temperature treatments on petal development by significantly increasing petal number through an increased production of petaloid stamens. In situ hybridization studies further revealed that low temperature restricts its spatial expression area. Analysis of DNA methylation level showed that low temperature treatment enhances the methylation level of the RhAG promoter, and a specific promoter region that was hypermethylated at CHH loci under low temperature conditions, was identified by bisulfite sequencing. This suggests that epigenetic DNA methylation contributes to the ambient temperature modulation of RhAG expression.DiscussionOur results provide highlights in the role of RhAG gene in petal number determination and add a new layer of complexity in the regulation of floral organ development.ConclusionsWe propose that RhAG plays an essential role in rose flower patterning by regulating petal development, and that low temperatures increase petal number, at least in part, by suppressing RhAG expression via enhancing DNA CHH hypermethylation of the RhAG promoter.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0623-1) contains supplementary material, which is available to authorized users.
Highlights
Flower development is central to angiosperm reproduction and is regulated by a broad range of endogenous and exogenous stimuli
We propose that r21">21]. The orthologue of AGAMOUS (RhAG) plays an essential role in rose flower patterning by regulating petal development, and that low temperatures increase petal number, at least in part, by suppressing RhAG expression via enhancing DNA CHH hypermethylation of the RhAG promoter
Flower patterning of RhAG-silencing flowers phenocopies low temperature treated flowers Since the expression of RhAG was reduced under low temperature conditions, we looked for evidence of causal relationship between RhAG function and the low temperature induced increase in petal number, by silencing RhAG in three month old rose plants using virusinduced gene silencing (VIGS)
Summary
Flower development is central to angiosperm reproduction and is regulated by a broad range of endogenous and exogenous stimuli. Genetic and molecular studies with several model plant species have shown that mutations in A-, B-, C-, and E-class genes all result in abnormal flowers, due to the replacement of one organ type by another [9,10,11]. Efforts have been made to characterize the genetic mechanisms involved in the formation of double flowers and studies of various species, including A. thaliana, have shown that loss of expression of AG results in the conversion of reproductive organs to perianth organs, as well as indeterminacy of the floral meristem, leading to showy double flowers [12,13,14,15]. Recent research has revealed that the microRNA miR172, which might be AG-independent, is a major factor in restricting AP2 activity, and that whether stamens or petals develop relies on the balance between AP2 and AG activity, rather than a mutual exclusion of the two genes [15]
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