Heterogeneous expression of the cotton R2R3-MYB transcription factor GbMYB60 increases salt sensitivity in transgenic Arabidopsis

MYB proteins form one of the largest transcription factor families in plants. Growing evidence has suggested that MYB has important roles in the regulation of plant growth and development, as well as responses to abiotic and biotic stresses. In the present study, the GbMYB60 gene isolated from Gossypium barbadense was heterogeneously expressed in Arabidopsis. GbMYB60 encodes a R2R3-MYB protein with transcriptional activation activity. Histochemical staining revealed that GbMYB60 was preferential expressed in the leaf vascular and meristem tissues of young seedlings and in the axillary bud tissue of mature plants. Expression pattern analysis indicated that GbMYB60 is induced by ABA, mannitol, and salt, but not H2O2. Transgenic Arabidopsis with constitutively higher expression of GbMYB60 exhibited reduced germination rates under salt and mannitol treatments as well as reduced tolerance to salt at the adult-plant stage. Transgenic Arabidopsis accumulates more reactive oxygen species compared to wild-type plants under stress conditions, corresponding with more severe cell death in transgenic plants. Additionally, ABA-related genes, including ABI5 and ABF3, were down-regulated in GbMYB60-overexpressing plants. This research has revealed that cotton GbMYB60 negatively regulates plant tolerance to salt stress, possibly through the inhibition of ABA signaling pathways and enhancing reactive oxygen species over-production.