AUTHOR=Song Guo-qing , Carter Benjamin B. , Zhong Gan-Yuan 

TITLE=Multiple transcriptome comparisons reveal the essential roles of FLOWERING LOCUS T in floral initiation and SOC1 and SVP in floral activation in blueberry

JOURNAL=Frontiers in Genetics

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/genetics/articles/10.3389/fgene.2023.1105519

DOI=10.3389/fgene.2023.1105519

ISSN=1664-8021

ABSTRACT=<p>The flowering mechanisms, especially chilling requirement-regulated flowering, in deciduous woody crops remain to be elucidated. Flower buds of northern highbush blueberry cultivar Aurora require approximately 1,000 chilling hours to bloom. Overexpression of a blueberry <italic>FLOWERING LOCUS T</italic> (<italic>VcFT</italic>) enabled precocious flowering of transgenic “Aurora” mainly in non-terminated apical buds during flower bud formation, meanwhile, most of the mature flower buds could not break until they received enough chilling hours. In this study, we highlighted two groups of differentially expressed genes (DEGs) in flower buds caused by <italic>VcFT</italic> overexpression (VcFT-OX) and full chilling. We compared the two groups of DEGs with a focus on flowering pathway genes. We found: 1) In non-chilled flower buds, VcFT-OX drove a high <italic>VcFT</italic> expression and repressed expression of a major MADS-box gene, blueberry <italic>SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1</italic> (<italic>VcSOC1</italic>) resulting an increased <italic>VcFT</italic>/<italic>VcSOC1</italic> expression ratio; 2) In fully chilled flower buds that are ready to break, the chilling upregulated <italic>VcSOC1</italic> expression in non-transgenic “Aurora” and repressed <italic>VcFT</italic> expression in VcFT-OX “Aurora”, and each resulted in a decreased ratio of <italic>VcFT</italic> to <italic>VcSOC1</italic>; additionally, expression of a blueberry <italic>SHORT VEGETATIVE PHASE</italic> (<italic>VcSVP</italic>) was upregulated in chilled flower buds of both transgenic and non-transgenic’ “Aurora”. Together with additional analysis of <italic>VcFT</italic> and <italic>VcSOC1</italic> in the transcriptome data of other genotypes and tissues, we provide evidence to support that <italic>VcFT</italic> expression plays a significant role in promoting floral initiation and that <italic>VcSOC1</italic> expression is a key floral activator. We thus propose a new hypothesis on blueberry flowering mechanism, of which the ratios of <italic>VcFT-</italic>to-<italic>VcSOC1</italic> at transcript levels in the flowering pathways determine flower bud formation and bud breaking. Generally, an increased <italic>VcFT/VcSOC1</italic> ratio or increased <italic>VcSOC1</italic> in leaf promotes precocious flowering and flower bud formation, and a decreased <italic>VcFT/VcSOC1</italic> ratio with increased <italic>VcSOC1</italic> in fully chilled flower buds contributes to flower bud breaking.</p>