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Transcriptome Profiling of Black Poplar under Boron Toxicity Revealed Genetic Regulation of Boron Uptake, Transport and Detoxification

ABSTRACT: Poplars are known to be highly tolerant species to boron toxicity and accumulation. However, genes and molecular networks responsible in boron toxicity tolerance have not been investigated yet. Therefore, we performed a pot experiment with 20 black poplar clones collected from the vicinity of boron mines and polluted areas to investigate its potential role in phytoremediation and to select the most boron toxicity tolerant genotype. Trees were treated with irrigation water containing seven elevated boron concentrations from 0 to 160 ppm. Then a microarray based comparative transcriptome profiling was conducted to identify boron toxicity regulated genes responsible in defence responses of black poplar. The results of the study indicated that black poplar is quite suitable for phytoremediation of boron pollution. It could resist 15 ppm soil B content and < 1600 mg/kg boron accumulation in leaves which are highly toxic concentrations for almost all agricultural plants. Transcriptomics results of study revealed totally 1625 and 1419 altered probe sets under boron toxicity in leaf and root tissues, respectively. The highest induction were recorded for the probes sets annotated to tyrosine aminotransferase, ATP binding cassette transporters, glutathione S transferases and metallochaperone proteins. Strong up regulation of these genes attributed to internal excretion of boron into the cell vacuole and existence of detoxification processes in black poplar. Many candidate genes functional in signalling, gene regulation, antioxidation, boron uptake, transport and detoxification processes were also identified in the current study. This is the first transcriptomic study identifying boron toxicity regulated poplar genes and their potential role in boron toxicity tolerance.

ORGANISM(S): Populus nigra Populus sp.

PROVIDER: GSE83745 | GEO | 2016/06/28

SECONDARY ACCESSION(S): PRJNA326913

REPOSITORIES: GEO

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Project description:Poplars are known to be highly tolerant species to boron toxicity and accumulation. However, genes and molecular networks responsible in boron toxicity tolerance have not been investigated yet. Therefore, we performed a pot experiment with 20 black poplar clones collected from the vicinity of boron mines and polluted areas to investigate its potential role in phytoremediation and to select the most boron toxicity tolerant genotype. Trees were treated with irrigation water containing seven elevated boron concentrations from 0 to 160 ppm. Then a microarray based comparative transcriptome profiling was conducted to identify boron toxicity regulated genes responsible in defence responses of black poplar. The results of the study indicated that black poplar is quite suitable for phytoremediation of boron pollution. It could resist 15 ppm soil B content and < 1600 mg/kg boron accumulation in leaves which are highly toxic concentrations for almost all agricultural plants. Transcriptomics results of study revealed totally 1625 and 1419 altered probe sets under boron toxicity in leaf and root tissues, respectively. The highest induction were recorded for the probes sets annotated to tyrosine aminotransferase, ATP binding cassette transporters, glutathione S transferases and metallochaperone proteins. Strong up regulation of these genes attributed to internal excretion of boron into the cell vacuole and existence of detoxification processes in black poplar. Many candidate genes functional in signalling, gene regulation, antioxidation, boron uptake, transport and detoxification processes were also identified in the current study. This is the first transcriptomic study identifying boron toxicity regulated poplar genes and their potential role in boron toxicity tolerance. Total RNA used in microarray experiment was isolated from the leaves and roots of black poplar clone; N.92.237 which accumulated the highest amount of boron its tissues. Total RNA used in the microarray experiment was isolated from leaves and roots of three black poplar saplings grown in ~ 2 ppm (control) and ~ 15 ppm (toxic) soil B contents. RNA isolation was made according to Lithium chloride precipitation method described in Chang et al. (1993). These three isolated RNAs (biological replicates) for each tissue loaded onto three Affymetrix poplar Gene Chips (technical replicates). Totally, 12 GeneChips (2 tissues Ã? 2 different B treatment Ã? 3 biological replicates) were used for transcriptional analysis.

Project description:Boron (B) is an essential nutrient for normal growth of plants. Despite its low abundance in soils, B pollution and toxicity have been reported to increase in especially arid and semi-arid environments. Poplars are known to be tolerant species to B toxicity and accumulation. In the current study, physiological, transcriptomic and hormonal regulations behind B toxicity response were investigated comparatively in poplar species. Previously identified clones of Populus nigra (P.n) and Populus alba (P.a) having contrasting B accumulation and leaf B toxicity symptoms were treated with elevated soil B supply in a pot trial. The physiological results of treatment indicated better biomass growth, higher leaf chlorophyll content and more than three folds lower B accumulation in leaves of P.a compared to P.n. Microarray based transcriptomic analysis revealed 1902 and 1006 differentially regulated transcripts for the leaves and roots of P.a, respectively. Several transcripts responsible in salicylic acid (SA) production (salicylic acid binding protein 2) and SA dependent gene regulation (chitinases, proteases, lipases and protease inhibitors) were strongly upregulated specifically in P.a tissues under B toxicity. Furthermore, endogenous SA content in the roots and leaves of P.a increased with a soil B concentration-dependent manner while there was no significant alteration in the same hormone for P.n tissues under B toxicity. Therefore, increase in endogenous SA concentration was strongly attributed to lower B uptake and B toxicity tolerance in P.a. In addition to SA mediated gene regulation, genes responsible in external excretion process was also supposed to be functional in P.a for reduction of tissue B content under toxic conditions. On the other hand, transcriptome profiling of P.n under B toxicity revealed 1624 and 1419 altered transcripts for the leaves and roots, respectively. Specific induction in transcripts annotated to ATP binding cassette B type transporters, glutathione S transferases and metallochaperones in P.n were linked to internal excretion of excess B in the species that could be related with much higher B uptake from the roots, directional transport to the leaves and detoxification under toxic B conditions.

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Transcriptome Profiling of Black Poplar under Boron Toxicity Revealed Genetic Regulation of Boron Uptake, Transport and Detoxification

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