Abstract
BackgroundAdverse environmental conditions severely influence various aspects of plant growth and developmental processes, causing worldwide reduction of crop yields. The C-repeat binding factors (CBFs) are critical transcription factors constituting the gene regulatory network that mediates the acclimation process to low temperatures. They regulate a large number of cold-responsive genes, including COLD-REGULATED (COR) genes, via the CBF-COR regulon. Recent studies have shown that the CBF transcription factors also play a role in plant responses to drought and salt stresses. Putative CBF gene homologues and their downstream genes are also present in the genome of Brachypodium distachyon, which is perceived as a monocot model in recent years. However, they have not been functionally characterized at the molecular level.ResultsThree CBF genes that are responsive to cold were identified from Brachypodium, designated BdCBF1, BdCBF2, and BdCBF3, and they were functionally characterized by molecular biological and transgenic approaches in Brachypodium and Arabidopsis thaliana. Our results demonstrate that the BdCBF genes contribute to the tolerance response of Brachypodium to cold, drought, and salt stresses by regulating downstream targets, such as DEHYDRIN5.1 (Dhn5.1) and COR genes. The BdCBF genes are induced under the environmental stress conditions. The BdCBF proteins possess transcriptional activation activity and bind directly to the promoters of the target genes. Transgenic Brachypodium plants overexpressing the BdCBF genes exhibited enhanced resistance to drought and salt stresses as well as low temperatures, and accordingly endogenous contents of proline and soluble sugars were significantly elevated in the transgenic plants. The BdCBF transcription factors are also functional in the heterologous system Arabidopsis. Transgenic Arabidopsis plants overexpressing the BdCBF genes were also tolerant to freezing, drought, and salt stresses, and a set of stress-responsive genes was upregulated in the transgenic Arabidopsis plants.ConclusionsTaken together, our results strongly support that the BdCBF transcription factors are key regulators of cold stress responses in Brachypodium and the CBF-mediated cold stress signaling pathway is conserved in this plant species. We believe that this study would confer great impact on stress biology in monocot species and could be applied to engineer abiotic stress tolerance of bioenergy grass species.
Highlights
Adverse environmental conditions severely influence various aspects of plant growth and developmental processes, causing worldwide reduction of crop yields
Through BLAST searches using the Arabidopsis CBF1, CBF2, and CBF3 proteins as baits, we identified 19 potential C-repeat binding factors (CBFs) homologues that have sequence similarities of higher than 50% throughout the full amino acid sequences to the Arabidopsis CBF proteins (Additional file 1)
We found that the BdCBF1 protein is a bona fide transcription factor, which binds to the promoters of cold-responsive genes from Arabidopsis and barley, suggesting that the BdCBF genes would be affected by abiotic stresses
Summary
Adverse environmental conditions severely influence various aspects of plant growth and developmental processes, causing worldwide reduction of crop yields. The C-repeat binding factors (CBFs) are critical transcription factors constituting the gene regulatory network that mediates the acclimation process to low temperatures. They regulate a large number of cold-responsive genes, including COLD-REGULATED (COR) genes, via the CBF-COR regulon. Putative CBF gene homologues and their downstream genes are present in the genome of Brachypodium distachyon, which is perceived as a monocot model in recent years They have not been functionally characterized at the molecular level. Plants frequently encounter abrupt environmental changes, such as temperature extremes and drought and salt stresses, in their natural habitats They have developed versatile defense mechanisms to cope with adverse growth conditions, which would underlie the astonishing diversity in plant architecture and physiology [1]. The promoters of many COR genes contain one or more copies of the widely conserved cis-acting element, C-repeat/ dehydration response element (CRT/DRE) having the CCGAC core sequence [9], indicating that multiple cold responses are coordinately regulated by common regulators
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