Abstract
BackgroundConstitutive expression of the CBF/DREB1 for increasing freezing tolerance in woody plants is often associated with other phenotypic changes including dwarf plant and delayed flowering. These phenotypic changes have been observed when Arabidopsis DWARF AND DELAYED FLOWERING 1 (DDF1) was overexpressed in A. thaliana plants. To date, the DDF1 orthologues have not been studied in woody plants. The aim of this study is to investigate transcriptomic responses to the overexpression of blueberry (Vaccinium corymbosum) DDF1 (herein, VcDDF1-OX).ResultsThe VcDDF1-OX resulted in enhanced freezing tolerance in tetraploid blueberry plants and did not result in significant changes in plant size, chilling requirement, and flowering time. Comparative transcriptome analysis of transgenic ‘Legacy-VcDDF1-OX’ plants containing an overexpressed VcDDF1 with non-transgenic highbush blueberry ‘Legacy’ plants revealed the VcDDF1-OX derived differentially expressed (DE) genes and transcripts in the pathways of cold-response, plant flowering, DELLA proteins, and plant phytohormones. The increase in freezing tolerance was associated to the expression of cold-regulated genes (CORs) and the ethylene pathway genes. The unchanged plant size, dormancy and flowering were due to the minimal effect of the VcDDF1-OX on the expression of DELLA proteins, flowering pathway genes, and the other phytohormone genes related to plant growth and development. The DE genes in auxin and cytokinin pathways suggest that the VcDDF1-OX has also altered plant tolerance to drought and high salinity.ConclusionA DDF1 orthologue in blueberry functioned differently from the DDF1 reported in Arabidopsis. The overexpression of VcDDF1 or its orthologues is a new approach to increase freezing tolerance of deciduous woody plant species with no obvious effect on plant size and plant flowering time.
Highlights
Constitutive expression of the CBF/DREB1 for increasing freezing tolerance in woody plants is often associated with other phenotypic changes including dwarf plant and delayed flowering
VcDDF1 and VcDDF1-OX in blueberry The VcDDF1 was initially designated as BB-CBF (GenBank: FJ222601.1) due to its similarity to A. thaliana CBF2, and this reasoning is valid when DELAYED FLOWERING 1 (DDF1) is not included in phylogenetic analysis [50]
Our designation of BB-CBF as VcDDF1 is the result of the phylogenetic analysis of A. thaliana CBF/DREB1 (i.e., CBF1, CBF2, CBF3, DDF1, and DDF2) and the blueberry-derived DRE1E_ARATH, DRE1A_ARATH, DRE1B_ARATH, and DRE1F_ORYSJ, which showed that BB-CBF is 52.5% similar to DDF1 compared 45.9% to CBF2 (Fig. 1a)
Summary
Constitutive expression of the CBF/DREB1 for increasing freezing tolerance in woody plants is often associated with other phenotypic changes including dwarf plant and delayed flowering These phenotypic changes have been observed when Arabidopsis DWARF AND DELAYED FLOWERING 1 (DDF1) was overexpressed in A. thaliana plants. Studies suggest that all plant species undergo cold acclimation through a similar process that belongs, at least partially, to the CBF/DREB1mediated cold-response pathway [1, 18,19,20,21]. This CBF/ DREB1 pathway has been documented in Arabidopsis thaliana [16, 22,23,24]. As global warming poses abiotic stresses (e.g., temperature changes and drought) to numerous plant species and threatens the world’s sustainable food production for a growing population, numerous studies have been done to evaluate the potential use of AP2/ERF transcription factors to enhance plant tolerance to abiotic stresses [28]
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