Overexpression of a stress-responsive MYB transcription factor of Poncirus trifoliata confers enhanced dehydration tolerance and increases polyamine biosynthesis.

MYBs are an important family of transcription factors that play significant roles in plant development and stress response in plants. However, knowledge concerning the functions of MYBs in the non-model plants and the target genes is still limited. In this study, we isolated a stress-responsive R2R3-type MYB gene from trifoliate orange (Poncirus trifoliata (L.) Raf.), designated as PtsrMYB. PtsrMYB shares the highest degree of identity with AtMYB109. Subcellular localization using onion epidermal cells indicates that PtsrMYB is localized in the nucleus. Transcript levels of PtsrMYB were up-regulated by abiotic stresses such as dehydration, salt, cold and ABA treatment. Overexpression of PtsrMYB in tobacco confers enhanced dehydration tolerance, as indicated by less water loss, lower levels of malondialdehyde and reactive oxygen species. The transgenic tobacco lines displayed higher mRNA levels of two arginine decarboxylase (ADC) genes before and after dehydration treatment when compared with the wild type, concurrent with the greater levels of polyamines. Several MYB-recognizing cis-acting elements exist on the promoters of PtADC gene. Yeast one-hybrid assay demonstrated that PtsrMYB predominantly interact with two regions of the promoter, indicating the PtADC may be a target gene of PtsrMYB. Take together, PtsrMYB plays a positive role in dehydration tolerance, which may be, at least in part, due to the modulation of polyamine synthesis by regulating the ADC gene.