Transcriptome analyses of Populus x euramericana clone I-214 leaves exposed to excess zinc.
Zinc (Zn) is an essential element for plant growth and development, but at high levels this metal can become toxic. Hyperaccumulator species are often not suitable for phytoremediation technologies because they need to be fast growing and have high biomass production, such as those of the Populus genus. Comparative genomics studies of poplars subjected to stress conditions such as heavy metal contamination have generated resources useful for improving the annotation of genes and have provided novel insights in the defense/tolerance mechanisms governing adaptation in non-hyperaccumulator plants. Using a microarray-based comparative analysis, we identified functional gene sets that are differentially regulated in the leaves of Populus × euramericana clone I-214 subjected to an excess but sub-lethal dose of Zn (1 mM). Eco-physiological and chemical analyses confirmed the results obtained in previous similar experiments. A total of 3861 expressed sequence tags (ESTs) were differentially expressed and grouped into two distinct libraries of up-regulated (40%) and down-regulated (60%) putative genes. The annotation of genes and gene products according to the Gene Ontology vocabularies was performed using Blast2GO software. The two transcriptome data sets were used to query all known Kyoto Encyclopedia of Genes and Genomes (KEGG) biosynthetic pathways of the genes identified in this study. The most represented molecular functions and biological processes were nucleotide binding and transcription, transport and response to stress and abiotic and biotic stimuli. The chloroplast, mitochondrion and their membrane systems were the cellular components most affected by excess Zn, as well as the photosynthetic, defense, sulfur and glutathione (GSH) metabolic pathways. The most up-regulated genes encoded electron carriers associated with ferrodoxin, the small subunit of ribulose-bisphosphate carboxylase oxygenase, and enzymes involved in GSH metabolism. This study is the most in-depth transcriptome and gene-annotation analysis of a hybrid poplar to date. The results are presented and critically discussed in terms of poplar response/tolerance to Zn stress for the characterization of non-hyperaccumulator phenotypes and the identification of candidate genes in perennial plants. These genetic findings provide useful information on tree species' adaptation to metal stress and provide powerful tools for the selection and/or genetic manipulation of stress-tolerant poplar clones.
BioLabs, Life Sciences Institute, Scuola Superiore Sant'Anna, Piazza Martiri della Libertà 33, I-56127 Pisa, Italy. dibaccio@sssup.it
Daniela
D
Di Baccio
Giulio
G
Galla
Tania
T
Bracci
Andrea
A
Andreucci
Gianni
G
Barcaccia
Roberto
R
Tognetti
Luca
L
Sebastiani
D053898:Biosynthetic Pathways / Q000187:drug effects / Q000235:genetics; D002734:Chlorophyll / Q000378:metabolism; D003433:Crosses, Genetic; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism; D020411:Oligonucleotide Array Sequence Analysis; D018515:Plant Leaves / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development; D032107:Populus / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development; D019655:Quantitative Trait, Heritable; D015032:Zinc / Q000633:toxicity*
D002734:Chlorophyll; D005978:Glutathione; D015032:Zinc