Comparative transcriptome analysis of nonchilled, chilled, and late-pink bud reveals flowering pathway genes involved in chilling-mediated flowering in blueberry

Guo-Qing Song,Qiuxia Chen

doi:10.1186/s12870-018-1311-8

Abstract

BackgroundBlueberry cultivars require a fixed quantity of chilling hours during winter endo-dormancy for vernalization. In this study, transcriptome analysis using RNA sequencing data from nonchilled, chilled, and late pink buds of southern highbush blueberry ‘Legacy’ was performed to reveal genes associated with chilling accumulation and bud break.ResultsFully chilled ‘Legacy’ plants flowered normally whereas nonchilled plants could not flower. Compared to nonchilled flower buds, chilled flower buds showed differential expression of 89% of flowering pathway genes, 86% of MADS-box genes, and 84% of cold-regulated genes. Blueberry orthologues of FLOWERING LOCUS T (FT) did not show a differential expression in chilled flower buds (compared to nonchilled flower bud) but were up-regulated in late-pink buds (compared to chilled flower bud). Orthologoues of major MADS-box genes were significantly up-regulated in chilled flower buds and down-regulated in late-pink buds. Functional orthologues of FLOWERING LOCUS C (FLC) were not found in blueberry. Orthologues of Protein FD (FD), TERMINAL FLOWER 1 (TFL1), and LEAFY (LFY) were down-regulated in chilled flower buds and in late-pink buds compared to nonchilled flower bud.ConclusionsThe changes from nonchilled to chilled and chilled to late-pink buds are associated with transcriptional changes in a large number of differentially expressed (DE) phytohormone-related genes and DE flowering pathway genes. The profile of DE genes suggests that orthologues of FT, FD, TFL1, LFY, and MADS-box genes are the major genes involved in chilling-mediated blueberry bud-break. The results contribute to the comprehensive investigation of the vernalization-mediated flowering mechanism in woody plants.

Highlights

Blueberry cultivars require a fixed quantity of chilling hours during winter endo-dormancy for vernalization
Orthologues of Protein FD (FD), TERMINAL FLOWER 1 (TFL1), and LEAFY (LFY) were down-regulated in chilled flower buds and in late-pink buds compared to nonchilled flower bud
The changes from nonchilled to chilled and chilled to late-pink buds are associated with transcriptional changes in a large number of differentially expressed (DE) phytohormone-related genes and DE flowering pathway genes

Summary

Introduction

Blueberry cultivars require a fixed quantity of chilling hours during winter endo-dormancy for vernalization. Under inductive low temperatures in the fall, deciduous woody fruit and nut crops are acclimated to develop freezing tolerance; accumulation of effective chilling hours is stimulated [3]. Climate change in the last 40 years has caused earlier shifts in the onset of the growing season for trees (e.g., 2.3 days/decade in temperate Europe) and increased temperature fluctuation [4]. Onset of the growing season causes insufficient chilling hours and prevents bud-break in fruit trees. Increased temperature fluctuation during plant bloom turns early season frosts into a danger, with freezing injuries to flowers and young fruits [5]. Plant breeding to manipulate chilling requirements and develop improved freeze tolerant cultivars are considered to be long-term solutions to mitigate reduced

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