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Series GSE7417

Query DataSets for GSE7417

Status

Public on Apr 03, 2007

Title

Gene expression profiling of chickpea responses to cold stress

Platform organisms

Cicer arietinum; Lathyrus sativus; Lens culinaris

Sample organism

Cicer arietinum

Experiment type

Expression profiling by array

Summary

‘Pulsechip’, a boutique cDNA microarray, generated from a set of chickpea (Cicer arietinum L.) unigenes, grasspea (Lathyrus sativus L.) ESTs and lentil (Lens culinaris Med.) resistance gene analogs, was employed to generate an expression profile of chickpea accessions tolerant and susceptible to cold stress. Two groups of a tolerant and susceptible accession were challenged with cold stress. The experiments were performed in three biological replications. The experiments were conducted in reference design where respective tissues from unstressed plants served as control. The leaves and flowers/buds/early pods tissues were collected and used for hybridization to measure changes in RNA abundance of treatment vs. control. The tissues from five experimental replicate plants per biological replication were pooled together (leaf and flower tissues separate) before RNA extraction. This RNA was used to prepare cDNA targets for expression analysis using microarray. The microarray had six technical replicate spots per EST. The transcript level for each EST/cDNA was firstly calculated as the average intensity of the six technical replicates and then the average intensity of three biological replicates. Data analysis included LOWESS normalization (LOcally WEighted polynomial regreSSion) to adjust for differences in quantity of initial RNA, labeling and detection efficiencies. A dye swap in one biological replicate adjusted dye bias, if any. The Differentially Expressed (DE) ESTs were identified as those with a 95% confidence interval for mean fold change (FC) that extended beyond the two-fold cut-off and also passed the Students t test (P<0.05) and FDR correction. These cut-offs translate into induced ESTs having a log2 ratio > 1 and repressed ESTs a ratio of < -1.
The analysis consisted of three fold comparison. Firstly, the ESTs that were differentially expressed between treatment and control plants of each accession were detected. Then the ESTs that were similarly expressed by tolerant and susceptible accessions were then eliminated by comparison. This included a two-way comparison, where tolerant and susceptible genotypes were compared within and between groups. Lastly, ESTs that were consensually differentially expressed between tolerant and susceptible accessions of the two batches were identified. The hypothesis was that if a putative gene was consistently expressed only in tolerant or susceptible genotype for a particular stress, it might be a candidate for tolerance/susceptibility for that stress.

Globally, the level of 221 transcripts was affected in response to cold stress in all the genotypes and tissue types studied. The DE transcripts in response to cold stress fell into various functional categories, indicating a broad response. Sixteen out of the 221 DE transcripts were consistently expressed in cold tolerant/susceptible genotypes. All these transcripts were repressed and none was found to be consistently induced in response to cold-stress. Most of the putative genes were identified in leaves of tolerant genotypes, and included a beta-galactosidase (DY475141) transcript that was possibly indicative of disaccharide (e. g. sucrose) retention with the effect of protecting cell membranes during cold stress. Several protein synthesis/modification and energy/metabolism transcripts were also repressed (e.g. DY475282, DY396371 and DY475555), which was likely due to the impairment of photosynthesis and respiration at low temperature. Other consistently repressed transcripts in tolerant genotypes included putative signalling (DY396262, DY475384 and DY396307) and defence-related proteins (CV793589 and DY396343), which may be involved in the repression of cell death mechanisms that are absent in tolerant genotypes. In susceptible genotypes, a putative superoxide dismutase precursor protein (DY475397) and sorting nexin protein (DY475523) were the only known transcripts to be consistently repressed.
Keywords: Chickpea, Cold stress, Tolerant, Susceptible, cDNA microarray

Overall design

Total RNA was extracted from separately pooled leaf and flowers/buds/early pods tissues for each genotype {Sonali (Tolerant1), Amethyst (Susceptible1), ILC 01276 (Tolerant2) and DOOEN (Susceptible2)} at each time-point (including control samples) using the RNeasy® Plant Mini Kit (Qiagen, Valencia, CA). The quantity and quality of the total RNA samples were assessed by OD260/OD280 ratios and gel electrophoresis respectively. Fluorescent-labeled targets were prepared and hybridized to array slides as described [Coram, TE. and Pang, ECK. 2006. Expression profiling of Chickpea genes differentially regulated during a resistance response to Ascochyta rabiei. Plant Biotechnology Journal. 4(6), 647–666]. All hybridizations were performed with six technical replicates and three biological replicates, incorporating dye-swapping (i.e. reciprocal labelling of Cy3 and Cy5) to eliminate any dye bias. Overall, 288 images were analyzed from 48 genotype x tissue type x treatment/control x biological replication condition.

Slides were scanned at 532 nm (Cy3 green laser) and 660 nm (Cy5 red laser) at 10 µm resolution using an Affymetrix® 428™ array scanner (Santa Clara, CA), and captured with the Affymetrix® Jaguar™ software (v. 2.0, Santa Clara, CA). Image analysis was performed using Imagene™ 5 (BioDiscovery, Marina Del Rey, CA) software. Quantified spot data was then compiled and transformed using GeneSight™ 3 (BioDiscovery, Marina Del Rey, CA). Data transformations consisted of a local background correction (mean intensity of background was subtracted from mean signal intensity for each spot), omitting flagged spots, LOWESS normalisation of the entire population, creating a Cy5/Cy3 mean signal ratio, taking a shifted log (base 2), and combination of duplicated spot data. To identify differentially expressed (DE) genes, expression ratio results were filtered to eliminate genes whose 95% confidence interval for mean fold change (FC) did not extend to 2-fold up or down, followed by Students t test with False Discovery Rate (FDR) multiple testing correction to retain only genes in which expression changes versus untreated control were significant at P < 0.05.

Contributor(s)

Mantri NL, Pang E, Ford R, Coram TE

Citation(s)

17764573

Submission date

Apr 01, 2007

Last update date

Mar 19, 2012

Contact name

Nitin Mantri

E-mail(s)

nitin_mantri@rediffmail.com