Constitutive Expression of an Apple FLC3-like Gene Promotes Flowering in Transgenic Blueberry under Nonchilling Conditions

MADS-box transcription factors FLOWERING LOCUS C (FLC) and APETALA1 (AP1)/CAULIFLOWER (CAL) have an opposite effect in vernalization-regulated flowering in Arabidopsis. In woody plants, a functional FLC-like gene has not been verified through reverse genetics. 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. An FLC3-like MADS-box gene from columnar apple trees (Malus domestica) (MdFLC3-like) was cloned for functional analysis through a constitutive transgenic expression. The MdFLC3-like shows 88% identity to pear’s FLC-like genes and 82% identity to blueberry’s CAL1 gene (VcCAL1). 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. 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. Thus, the constitutively expressed MdFLC3-like in transgenic blueberries functioned likely as a blueberry’s VcCAL1. The results are anticipated to facilitate future studies for revealing chilling-mediated flowering mechanisms in woody plants.