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STOP1 Regulates LKS1 Transcription and Coordinates K + /NH 4 + Balance in Arabidopsis Response to Low-K + Stress.

Zhi-Fang WangTing-Wei MiYong-Qiang GaoHan-Qian FengWei-Hua WuYi Wang
Published in: International journal of molecular sciences (2021)
Potassium and nitrogen are essential mineral elements for plant growth and development. The protein kinase LKS1/CIPK23 is involved in both K + and NH 4 + uptake in Arabidopsis root. The transcripts of LKS1 can be induced by low K + (0.1 mM) and high NH 4 + (30 mM); however, the molecular mechanism is still unknown. In this study, we isolated the transcription factor STOP1 that positively regulates LKS1 transcription in Arabidopsis responses to both low-K + and high-NH 4 + stresses. STOP1 proteins can directly bind to the LKS1 promoter, promoting its transcription. The stop1 mutants displayed a leaf chlorosis phenotype similar to lks1 mutant when grown on low-K + and high-NH 4 + medium. On the other hand, STOP1 overexpressing plants exhibited a similar tolerant phenotype to LKS1 overexpressing plants. The transcript level of STOP1 was only upregulated by low K + rather than high NH 4 + ; however, the accumulation of STOP1 protein in the nucleus was required for the upregulation of LKS1 transcripts in both low-K + and high-NH 4 + responses. Our data demonstrate that STOP1 positively regulates LKS1 transcription under low-K + and high-NH 4 + conditions; therefore, LKS1 promotes K + uptake and inhibits NH 4 + uptake. The STOP1/LKS1 pathway plays crucial roles in K + and NH 4 + homeostasis, which coordinates potassium and nitrogen balance in plants in response to external fluctuating nutrient levels.
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