The results are anticipated to facilitate future studies for revealing chilling-mediated flowering mechanisms in woody plants. Surprisingly, we found for the first time that constitutive expression of the MdFLC3-like in transgenic blueberry plants promoted flowering under nonchilling conditions where nontransgenic could not flower. Functional analysis of the MdFLC3-like through constitutive expression was conducted in transgenic highbush blueberry cv. To study the molecular mechanism of chilling-mediated flowering in woody plants, we cloned an FLC-like MADS-box gene from columnar apple trees ( MdFLC3-like). To date, functional FLC orthologues have not been identified in woody fruit crops. In apples, transcription profiling of chilled buds has revealed the potential roles of FLC-like, FT-like and TERMINAL FLOWER 1-like ( TFL1-like) genes. Modifying the flowering initiation pathway is one of the most important improvement properties for these two fruit crops. Īpples ( Malus domestica) and highbush blueberries ( Vaccinium corymbosum L.) need sufficient chilling exposure to release bud dormancy. Overexpression of birch BpAP1 in tobacco and birch also generated early flowering and dwarf phenotypes. Overexpression of apple AP1-like genes, MdMADS2 and MdMADS5, induced early flowering in both tobacco and Arabidopsis. For example, constitutive overexpression of AtAP1 in citrus showed flowering initiation in the first year. Ectopic expression AP1 genes in other plant species also showed early flowering phenotypes. Genetic evidence showed that either single or double AP1/CAL mutants led to abnormal floral morphology in flower development. Overexpression of AP1 gene promoted transition from apical or lateral shoots into flowers and early flowering phenotype in transgenic Arabidopsis. LFY was shown to directly activate the expression of AP1/CAL in floral primordial and then produce a positive feedback effect on its own expression. In contrast, AP1/CAL positively promotes the expression of floral meristem identity genes in synergy with FRUITFULL ( FUL) and LEAFY ( LFY). Constitutive expression of FLC often delays flowering and causes abnormal floral morphological changes, such as short stamens, reduction of pollen amount, and larger carpels in transgenic plants. FLC represses the expression of two major flowering genes, FLOWERING LOCUS T ( FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 ( SOC1). MADS-box transcription factors FLOWERING LOCUS C ( FLC) and APETALA1 ( AP1)/ CAULIFLOWER ( CAL) perform an opposite function in vernalization-regulated flowering initiation in Arabidopsis. The results are anticipated to facilitate future studies for revealing chilling-mediated flowering mechanisms in woody plants.Įxposure to low temperatures (i.e., vernalization) promotes the transition from vegetative to reproductive phase of plant development in most annually flowering species. Thus, the constitutively expressed MdFLC3-like in transgenic blueberries functioned likely as a blueberry’s VcCAL1. As a consequence, in contrast to the anticipated late flowering associated with an overexpressed FLC-like, the MdFLC3-like promoted flowering of transgenic blueberry plants under nonchilling conditions where nontransgenic ‘Legacy’ plants could not flower. When constitutively expressed in a highbush blueberry ( Vaccinium corymbosum L.) cultivar ‘Legacy’, the MdFLC3-like induced expressions of orthologues of three MADS-box genes, including APETALA1, SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1, and CAL1. The MdFLC3-like shows 88% identity to pear’s FLC-like genes and 82% identity to blueberry’s CAL1 gene ( VcCAL1). An FLC3-like MADS-box gene from columnar apple trees ( Malus domestica) ( MdFLC3-like) was cloned for functional analysis through a constitutive transgenic expression. To reveal chilling-regulated flowering mechanisms in woody fruit crops, we conducted phylogenetic analysis of the annotated FLC-like proteins of apple and found that these proteins are grouped more closely to Arabidopsis AP1 than the FLC group. In woody plants, a functional FLC-like gene has not been verified through reverse genetics. MADS-box transcription factors FLOWERING LOCUS C ( FLC) and APETALA1 ( AP1)/ CAULIFLOWER ( CAL) have an opposite effect in vernalization-regulated flowering in Arabidopsis.
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