The effect of 24-epibrassinolide on gene expression related to cell walls under boron deficiency and toxicity in the leaves of Arabidopsis thaliana

The changing composition of plant cell walls allows for the continuation of the existing structure under normal conditions and also the protection of physical integrity under altering environmental conditions. In this study, the possible effects of the 24-Epibrassinolide (EBL) hormone under boron (B) deficiency and toxicity conditions on the expression of cell wall-related genes [cellulose synthase (CESA), expansin (EXP), xyloglucan endotransglucosylase/hydrolase (XTH) and pectin methylesterase (PME)] were investigated in the rosette leaves of Arabidopsis thaliana. For this purpose, 0 or 3000 µM of boric acid (BA) and/or 1 µM of EBL were applied to the plants which were grown in a hydroponic medium for five and ten weeks. While B-toxicity elevated the mRNA levels of the CESA4 and CESA8 genes in the leaves of the five-week-old plants, B-stress (B-deficiency and -toxicity) caused an increase in the expression of the CESA4, CESA6, and CESA8 genes in the ten-weekold plants. The transcript levels of the EXPA5 gene increased under B-stress in the ten-week-old plants whereas the expression of the EXPA8 gene decreased when compared to the control at two developmental stages. Co-treatment of EBL and Bstress strongly elevated the transcript level of the EXPA5 gene in the ten-week-old plants and the EXPA8 gene at both developmental stages. The EXPA14 and XTH23 genes exhibited distinct expression profiles under B-deficiency and -toxicity in both the five- and ten-week-old plants. The transcript level of the XTH21 gene was upregulated in the leaves of the plants exposed to B-stress. The mRNA level of the PME2 and PME41 genes was generally upregulated in response to B-stress in both the five- and ten-week-old plants. 24-Epibrassinolide alone and in combination with B-stress led to a remarkable increase in the expression of the XTH and PME genes compared to the control. These results demonstrate that cell wall genes generally show a similar pattern of expression at both developmental stages and the EBL hormone induces changes in the expression levels of cell wall-related genes under B-stress.