CBF/DREB转录因子与植物矮化的相关性研究进展

CBF/DREB转录因子即干旱应答元件结合蛋白,是一类可以调控多个与干旱、高盐及低温耐性有关的功能基因表达的转录因子家族。很多报道称CBF/DREB转录因子的过量表达使转基因植株产生矮化、晚花现象。着重探讨CBF/DREB转录因子与植物矮化现象相关性与其矮化机理,并对草坪草育种新方向进行展望。     

Organization and expression of two Arabidopsis DREB2 genes encoding DRE-binding proteins involved in dehydration- and high-salinity-responsive gene expression

In plants, a cis-acting element, DRE/CRT, is involved in ABA-independent gene expression in response to dehydration and low-temperature stress. To understand signal transduction pathways from perception of the dehydration stress signal to gene expression, we characterized a gene family for DRE/CRT-binding proteins DREB2A and DREB2B in Arabidopsis thaliana. Northern analysis showed that both genes are induced by dehydration and high-salt stress. Organ-specific northern analysis with gene-specific probes showed that these genes are strongly induced in roots by high-salt stress and in stems and roots by dehydration stress. The DREB2A gene is located on chromosome 5, and DREB2B on chromosome 3. We screened an Arabidopsis genomic DNA library with cDNA fragments of DREB2A and DREB2B as probes, and isolated DNA fragments that contained 5-flanking regions of these genes. Sequence analysis showed that both genes are interrupted by a single intron at identical positions in their leader sequence. Several conserved sequences were found in the promoter regions of both genes. The -glucuronidase (GUS) reporter gene driven by the DREB2 promoters was induced by dehydration and high-salt stress in transgenic Arabidopsis plants.     

Characterization of the novel gene BjDREB1B encoding a DRE-binding transcription factor from Brassica juncea L

A novel DREB (dehydration responsive element binding protein) gene, designated BjDREB1B, was isolated from Brassica juncea L. BjDREB1B contains a conserved EREBP/AP2 domain and was classified into the A-1 subgroup of the DREB subfamily based on phylogenetic tree analysis. RT-PCR showed that BjDREB1B was induced by abiotic stresses and exogenous phytohormones, such as drought, salt, low temperature, heavy metals, abscisic acid, and salicylic acid. Gel shift assay revealed that BjDREB1B specifically bound to the DRE element in vitro. Yeast one-hybrid assay showed that full-length BjDREB1B or its C-terminal region functioned effectively as a trans-activator. Furthermore, overexpression of BjDREB1B in tobacco up-regulated the expression of NtERD10B, and BjDREB1B transgenic plants accumulated higher levels of proline than control plants under normal and saline conditions, together showing that BjDREB1B plays important roles in improving plant tolerance to drought and salinity.     

A novel calcium-dependent protein kinase gene from Populus euphratica, confers both drought and cold stress tolerance

Populus species are the most important timber trees over the Northern hemisphere. Most of them are cold- and drought-sensitive except the Populus euphratica Oliv. Here, a calcium-dependent protein kinase (CDPK) gene cloned from P. euphratica, designated as PeCPK10, was rapidly induced by salt, cold, and drought stresses. The protein encoded by PeCPK10 was localized within the nucleus and cytosol, which may be important for its specific regulation in cellular functions. To elucidate the physiological functions of PeCPK10, we generated transgenic Arabidopsis plants overexpressing PeCPK10. The results showed that PeCPK10-transgenic lines experienced better growth than vector control plants when treated with drought. Stronger abscisic acid-induced promotion of stomatal closing has been showed in transgenic lines. Particularly, overexpression of PeCPK10 showed enhanced freezing tolerance. Constitutive expression of PeCPK10 enhanced the expression of several abscisic acid-responsive genes and multiple abiotic stress-responsive genes such as RD29B and COR15A. Accordingly, a positive regulator responsive to cold and drought stresses in P. euphratica is proposed.     

CbCBF from Capsella bursa-pastoris enhances cold tolerance and restrains growth in Nicotiana tabacum by antagonizing with gibberellin and affecting cell cycle signaling

Plant cells respond to cold stress via a regulatory mechanism leading to enhanced cold acclimation accompanied by growth retardation. The C-repeat binding factor (CBF) signaling pathway is essential for cold response of flowering plants. Our previously study documented a novel CBF-like gene from the cold-tolerant Capsella bursa-pastoris named CbCBF, which was responsive to chilling temperatures. Here, we show that CbCBF expression is obviously responsive to chilling, freezing, abscisic acid, gibberellic acid (GA), indoleacetic acid or methyl jasmonate treatments and that the CbCBF:GFP fusion protein was localized to the nucleus. In addition, CbCBF overexpression conferred to the cold-sensitive tobacco plants enhanced tolerance to chilling and freezing, as well as dwarfism and delayed flowering. The leaf cells of CbCBF overexpression tobacco lines attained smaller sizes and underwent delayed cell division with reduced expression of cyclin D genes. The dwarfism of CbCBF transformants can be partially restored by GA application. Consistently, CbCBF overexpression reduced the bioactive gibberellin contents and disturbed the expression of gibberellin metabolic genes in tobacco. Meanwhile, cold induced CbCBF expression and cold tolerance in C. bursa-pastoris are reduced by GA. We conclude that CbCBF confers cold resistance and growth inhibition to tobacco cells by interacting with gibberellin and cell cycle pathways, likely through activation of downstream target genes.     

Mutations in AP22.65 accelerate flowering in Arabidopsis thaliana

Identification of the gene(s) responsible for flowering time in Arabidopsis has significant implications. We used the T-DNA insertion library of Arabidopsis thaliana to screen an early-flowering mutant that exhibits accelerated flowering under short-day conditions. AP22.65, a novel flowering-time gene in that species, was isolated and identified via genome-walking and bioinformatics analysis. The flowering time of AP22.65-complementing plants was similar to that of the Col-0 wild type (WT). Conversely, its overexpression delayed flowering. Consistent with this phenotype, expression of AP22.65 was decreased in the ap22.65-1 mutant, recovered in AP22.65-complementing plants, and increased in AP22.65-overexpressing plants. Compared with the WT, expression levels of critical genes in different flowering pathways, i.e., SPY, FLC, GI, CO, FT, and LFY, were down-regulated in loss-of-function mutants. Expression of AP22.65 was distributed in flowers, siliques, rosette leaves, and whole seedlings. Therefore, this gene may be a negative regulator of Arabidopsis flowering.