Transcriptional profiling of pea ABR17 mediated changes in gene expression in Arabidopsis thaliana

Abstract

Background: Pathogenesis-related proteins belonging to group 10 (PR10) are elevated in response to biotic and abiotic stresses in plants. Previously, we have shown a drastic salinity-induced increase in the levels of ABR17, a member of the PR10 family, in pea. Furthermore, we have also demonstrated that the constitutive expression of pea ABR17 cDNA in Arabidopsis thaliana and Brassica napus enhances their germination and early seedling growth under stress. Although it has been reported that several members of the PR10 family including ABR17 possess RNase activity, the exact mechanism by which the aforementioned characteristics are conferred by ABR17 is unknown at this time. We hypothesized that a study of differences in transcriptome between wild type (WT) and ABR17 transgenic A. thaliana may shed light on this process.

Results: The molecular changes brought about by the expression of pea ABR17 cDNA in A. thaliana in the presence or absence of salt stress were investigated using microarrays consisting of 70-mer oligonucleotide probes representing 23,686 Arabidopsis genes. Statistical analysis identified number of genes which were over represented among up- or down-regulated transcripts in the transgenic line. Our results highlight the important roles of many abscisic acid (ABA) and cytokinin (CK) responsive genes in ABR17 transgenic lines. Although the transcriptional changes followed a general salt response theme in both WT and transgenic seedlings under salt stress, many genes exhibited differential expression patterns when the transgenic and WT lines were compared. These genes include plant defensins, heat shock proteins, other defense related genes, and several transcriptional factors. Our microarray results for selected genes were validated using quantitative real-time PCR.

Conclusion: Transcriptional analysis in ABR17 transgenic Arabidopsis plants, both under normal and saline conditions, revealed significant changes in abundance of transcripts for many stress responsive genes, as well as those related to plant growth and development. Our results also suggest that ABR17 may mediate stress tolerance through the modulation of many ABA- and CK-responsive genes and may further our understanding of the role of ABR17 in mediating plant stress responses.

Figure 1

Appearance of WT and ABR17 transgenic A. thaliana at various growth stages: Seedlings at 5, 14 days (A), 21 days (B), 28 days (C) and MS-grown 14-day-old seedlings (D) are shown.

Figure 2

Appearance of WT and ABR17 transgenic A. thaliana in response to treatments. (A) Appearance of WT and transgenic ABR17 A. thaliana seedlings grown on MS media with 100 mM NaCl (B) Appearance of 7-day-old WT and ABR17 transgenic A. thaliana seedlings grown under dark.

Figure 3

Pea ABR17-modulated transcriptional changes of selected genes. Transcriptional changes of a selected number of transcripts as identified by microarrays, and their validation using qRT- PCR and effects of CK on these genes in WT A. thaliana is given here. The values represented in the graph are fold changes of transcript abundance between transgenic ABR17-A. thaliana seedlings versus WT seedlings grown under normal conditions. Error bars are standard error of fold changes driven from (n = 3) three biological replicates. The AGI annotations are as follows: At5g44420-Plant defensin protein family member PDF1.2, Low-molecular-weight cysteine-rich (LCR77); At3g45970-ATEXLA1 (A. thaliana expansin-like A1); At1g07135-Glycine rich protein; and At1g01560-ATMPK11.

Figure 4

Transcript abundance of selected genes in salt treated-WT and ABR17 transgenic A. thaliana seedlings. The values represented in the graph are fold changes of transcript abundance as identified by microarrays and their validation using qRT-PCR, between salt treated (100 mM) seedlings versus untreated seedlings either in wild type or in ABR17 transgenic A. thaliana. Error bars are standard error of fold changes driven from (n = 3) three biological replicates. The AGI annotations are as follows:At3g02480-ABA-responsive protein-related; At5g43650-basic helix-loop-helix (bHLH) family protein; At5g24640-unknown protein; At4g25810-XTR6: Xyloglucan endotransglycosylase 6; At1g43160-ethylene-responsive transcription factor Related to Apetala 2.6 (Protein RAP2.6); At3g15500-ATNAC3 (A. thaliana NAC domain containing protein 55); At4g14400-ACD6 (Accelerated cell death 6); At1g14880-PLAC8 domain containing protein; At5g44420-Plant defensin protein family member PDF1.2; At3g45970- ATEXLA1 (A. thaliana expansin-like A1); At1g07135-Glycine rich protein; and At1g01560: ATMPK11 (A. thaliana MAP kinase 11). † : the fold change in here is 272.27 ± 58.5.