Constitutive expression of an apple gene promotes flowering in transgenic blueberry under nonchilling conditions

Authors: ZONG, XIAOJUAN - Michigan State University; ZHANG, YUGANG - Michigan State University; WALWORTH, AARON - Michigan State University; TOMASZEWSKI, ELISE - Michigan State University; CALLOW, PETE - Michigan State University; Zhong, Gan-Yuan; SONG, GUO-QING - Michigan State University

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2019
Publication Date: 6/6/2019
Citation: Zong, X., Zhang, Y., Walworth, A., Tomaszewski, E.M., Callow, P., Zhong, G., Song, G. 2019. Constitutive expression of an apple FLC3-like gene promotes flowering in transgenic blueberry under nonchilling conditions. International Journal of Molecular Sciences. 20(11):2775. https://doi.org/10.3390/ijms20112775.
DOI: https://doi.org/10.3390/ijms20112775

Interpretive Summary: Climate changes have resulted in early onset of growing seasons and increased temperature fluctuations. Consequently, early onset of the growing seasons causes insufficient chilling (not enough chill hours to stimulate dormancy release and seasonal growth of vegetative and floral buds) for fruit trees, and increased temperature fluctuations during plant blooming turn early-season frosts into freezing injuries to flowers and young fruits. To secure deciduous fruit production, manipulating chilling requirements and cold/freezing tolerance through plant breeding is considered to be a long-term solution to mitigate the potential threats of climate changes. Developing cultivars with a low chilling requirement may help expand the cultivation areas of temperate deciduous fruit trees in warm areas and may also secure high profitability of protected cultivation in greenhouses. Apples and highbush blueberries both need sufficient chilling exposure to release bud dormancy. We identified a gene (an FLC-like MADS-box) likely involved in chilling responses from columnar apple trees and evaluated it in transgenic highbush blueberry cv. Legacy. Surprisingly, we found for the first time that expression of the FLC-like gene in transgenic blueberry plants promoted flowering under non-chilling conditions where control could not flower. The results provided an important understanding of chilling-mediated flowering mechanisms in woody plants.

Technical Abstract: 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.