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

• Main Authors: Xiaojuan Zong, Yugang Zhang, Aaron Walworth, Elise M. Tomaszewski, Pete Callow, Gan-yuan Zhong, Guo-qing Song
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: International Journal of Molecular Sciences
• Subjects: chilling requirement; dormancy release; FLOWERING LOCUS C; flowering time; MADS-box gene; woody plants
• Online Access: https://www.mdpi.com/1422-0067/20/11/2775

MADS-box transcription factors <i>FLOWERING LOCUS C</i> (<i>FLC</i>) and <i>APETALA1</i> (<i>AP1</i>)/<i>CAULIFLOWER</i> (<i>CAL</i>) have an opposite effect in vernalization-regulated flowering in <i>Arabidopsis</i>. In woody plants, a functional <i>FLC-like</i> 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 <i>FLC-like</i> proteins of apple and found that these proteins are grouped more closely to <i>Arabidopsis AP1</i> than the <i>FLC</i> group. An <i>FLC3-like</i> MADS-box gene from columnar apple trees (<i>Malus domestica</i>) (<i>MdFLC3-like</i>) was cloned for functional analysis through a constitutive transgenic expression. The <i>MdFLC3-like</i> shows 88% identity to pear&#8217;s <i>FLC-like</i> genes and 82% identity to blueberry&#8217;s <i>CAL1</i> gene (<i>VcCAL1</i>). When constitutively expressed in a highbush blueberry (<i>Vaccinium corymbosum</i> L.) cultivar &#8216;Legacy&#8217;, the <i>MdFLC3-like</i> induced expressions of orthologues of three MADS-box genes, including <i>APETALA1</i>, <i>SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1</i>, and <i>CAL1</i>. As a consequence, in contrast to the anticipated late flowering associated with an overexpressed <i>FLC-like</i>, the <i>MdFLC3-like</i> promoted flowering of transgenic blueberry plants under nonchilling conditions where nontransgenic &#8216;Legacy&#8217; plants could not flower. Thus, the constitutively expressed <i>MdFLC3-like</i> in transgenic blueberries functioned likely as a blueberry&#8217;s <i>VcCAL1</i>. The results are anticipated to facilitate future studies for revealing chilling-mediated flowering mechanisms in woody plants.