|ShuaiZhao,Mei-Ling Zhang,Tian-LiMa,and Yi Wang.Phosphorylation of ARF2 Relieves Its Repression of Transcription of the K+ Transporter Gene HAK5 in Response to Low Potassium Stress.The Plant Cell.DOI:10.1105/tpc.16.00684|
Phosphorylation of ARF2 Relieves Its Repression of Transcription of the K+ Transporter Gene HAK5 in Response to Low Potassium Stress
ShuaiZhao,Mei-Ling Zhang,Tian-LiMa,and Yi Wang
The Plant Cell
Potassium (K+)plays crucial roles inplant growth and development. Innatural environments, K+ availability in soils isrelatively low and ﬂuctuating. Transcriptional regulation of K+ transporter genes is one of the most important mechanisms in the plant’s response to K+ deﬁciency. In this study, we demonstrated that the transcription factor ARF2 (Auxin Response Factor 2) modulates the expression of the K+ transporter gene HAK5 (High Afﬁnity K+ transporter 5) in Arabidopsis thaliana. The arf2 mutant plants showed a tolerant phenotype similar to the HAK5-overexpressing lines on low-K+ medium, whose primary root lengths were longer than those of wild-type plants. High-afﬁnity K+ uptake was signiﬁcantly increased in these plants. ARF2overexpressing lines and the hak5 mutant were both sensitive to low-K+ stress. Disruption of HAK5 in the arf2 mutant abolished the low-K+-tolerant phenotype of arf2. As a transcriptional repressor, ARF2 directly bound to the HAK5 promoter and repressed HAK5 expression under K+ sufﬁcient conditions. ARF2 can be phosphorylated after low-K+ treatment, which abolished its DNA binding activity to the HAK5 promoter and relieved the inhibition on HAK5 transcription. Therefore, HAK5 transcript could be induced, and HAK5-mediated high-afﬁnity K+ uptake was enhanced under K+ deﬁcient conditions. The presented results demonstrate that ARF2 plays important roles in the response to external K+ supply in Arabidopsis and regulates HAK5 transcription accordingly.