No abstract

Earlier our colleagues detected that the genes related to jasmonate (JA), ethylene, and cell wall modification were significantly regulated under boron (B) toxicity in wheat. Determination of regulation mechanisms of these novel genes under B toxicity is very important in Arabidopsis thaliana as a model plant. As key regulators, the microRNAs (miRNAs) regulate gene expression at the posttranscriptional level and respond to numerous abiotic stresses in plants. In this study, expression levels of miRNAs such as miR159, miR172, miR319, and miR394 targeting JA and ethylene-related transcription factors and also miR397 targeting laccase were determined in Arabidopsis thaliana under toxic B conditions. Stem-loop quantitative reverse transcription polymerase chain reaction was used to amplify mature miRNAs for expression analyses. Expression levels of miRNAs targeting transcription factors related to JA and ethylene metabolisms were induced remarkably in moderate B toxicity (condition 1B) but not in severe B toxicity (condition 3B). Most remarkable regulations were obtained in miR172 and miR319 in Arabidopsis thaliana. Expression level of miR397 did not remarkably change under B toxicity, indicating a lack of posttranscriptional regulation of laccase related to cell wall modification. Moreover, miRNAs targeting transcription factors related to JA and ethylene metabolisms might be oxidative stress-adaptive responses of Arabidopsis to B toxicity.

Post transcriptional gene regulation in wheat cultivars caused by boron (B) toxicity has not been reported to date. In this study, two wheat cultivars Bolal-2973 (B-tolerant) and Atay-85 (Bsensitive) were compared with regard to the transcriptional regulation of miR319, miR172 and miR398 and their plausible target genes in order to address differences in their performances under high B levels. The expression levels of Cu/ZnSOD gene were found to be greater in Atay exposed to toxic B compared to Bolal, as verified by stable expression level of miR398. In wheat cultivars, both toxic B concentrations might cause an induction of leaf senescence mechanism due to stable level of JA and ethylene-related miRNAs, miR172 and miR319. miR172 targeting transcription factor TOE1 was only induced under B toxicity in sensitive cultivar Atay. However, MYB3 as target of miR319 were significantly upregulated under toxic B in both cultivars. Also, computational prediction of these miRNA targets in wheat was performed and their orthologs in Arabidopsis thaliana were determined. Functional protein association networks of proteins encoded by miRNA targets and gene ontology enrichment analyses of these genes were identified. We identified new sets of genes that are targets of miR172, miR319 and miR398 in T. aestivum. In addition, miR172, miR319 and miR398 are responsive to different nutrient deficiencies or toxicities such as Fe, P, B, S and Cu, suggesting crosstalk between the post-transcriptional regulatory mechanisms involving miRNAs in plants.

No abstract

The fine-tuned regulation of the Halliwell-Asada cycle (ascorbate-glutathione pathway) in Arabidopsis thaliana under boron (B) toxicity was shown in our previous report. In this study, we investigated the expression levels of some members of the glutathione S-transferase (GST) superfamily, such as phi (GSTF2, GSTF6, GSTF7, and GSTF8), tau (GSTU19), and zeta (GSTZ1) classes in Arabidopsis thaliana that were exposed to 1 mM boric acid (1B) and 3 mM boric acid (3B). Additionally, the expression levels of genes for glutathione (GSH) and phytochelatin biosynthesis as well as miR169 and miR156 were evaluated in Arabidopsis thaliana exposed to 1B and 3B. Moreover, changes in the levels of total GST activity; GSH; and total, protein-bound, and nonprotein thiols were spectrophotometrically determined. GSH levels and nonprotein thiol content did not change significantly following both B-toxicity conditions. Expression levels of GSH1 and GSH2 stayed stable under 1B toxicity; however, GSH1 expression increased significantly under 3B conditions in Arabidopsis thaliana. The expression levels of four genes from phi class members of GST were not dramatically changed under B-toxicity conditions. However, the transcript levels of miR169, ATGSTU19, and ATGSTZ1 were significantly increased after 1B and 3B exposure. These GST genes may have a role in the dramatic increase of total GST activity under toxic B. To the best of our knowledge, this is the first report displaying an integrative view of high-B-induced regulation of GSH-dependent enzymatic machinery at different biological organization levels in Arabidopsis thaliana.