The involvement of the induction of anthocyanin biosynthesis and transport in toxic boron responsive regulation in Arabidopsis thaliana

Abstract

Recently, boron (B) has been found to form a complex with anthocyanin, which could be evidence for the B tolerance mechanisms that reduce free B in the leaf tissues of plants. However, the molecular mechanism of anthocyanin biosynthesis and transport has not been satisfactorily elucidated in plants exposed to toxic B. Therefore, the changes in expression levels of some of the phenylpropanoid pathway genes, early and late flavonoid biosynthetic genes, and transcription factors related to anthocyanin biosynthesis and transport were determined in Arabidopsis thaliana under B toxicity. Accordingly, 1 mM boric acid treatment did not cause any significant change in the expression levels of anthocyanin biosynthesis genes such as PAL1, PAL2, C4H, 4CL3, CHS, ANS and transcription factors such as MYBD and TT8 in Arabidopsis thaliana. However, 3 mM boric acid treatment induced the expression levels of anthocyanin biosynthesis genes such as C4H, 4CL3 and transcription factors including MYB75, MYB114 and anthocyanin transporter genes such as TT13 and TT19. In addition to B-anthocyanin, B-anthocyanins conjugated with glutathione (GSH) complexes can also participate in the internal B tolerance mechanism in plants. Therefore, the direct role of the B-anthocyanin complex without GSH conjugation needs to be determined. For this purpose, anthocyanin accumulation was determined in slim1 mutant Arabidopsis thaliana exposed to excess B because SLIM1 transcription factor activates sulfate acquisition for S assimilation, which generates cysteine, the substrate for GSH. Accordingly, it was gradually increased through increasing toxic B levels in both wild type (WT) and slim1 mutant plants. slim1 mutant had more anthocyanin accumulation than WT under control and all toxic B conditions. In conclusion, increases in expression levels of MYB75, MYB114, TT13, TT19 and in anthocyanin level in slim1 mutant in response to increased toxic B levels showed that anthocyanins may play a primary role in B tolerance in plants.