FUNCTIONAL CHARACTERIZATION OF ZmHAK1 PROMOTERAND ITS REGULATORY TRANSCRIPTION FACTORS IN MAIZE
Potassium (K<sup>+</sup>) deficiency in the soil may seriously affect the yield and quality of plants, which usually satisfy their potassium requirements by engaging their K<sup>+</sup> transporters and/or channels. High-affinity potassium transporter (ZmHAK) family members play crucial role in the uptake and distribution of K<sup>+</sup> in maize (Zea mays L.). Here, we describe the function of ZmHAK1 promoter and its upstream regulatory transcription factors in maize. In this plant, HAK gene family includes 34 protein-encoding members, with their phylogenetic tree analysis showing both evolutionary conservativeness and diversity. ZmHAK1 gene promoter contains many functional elements related to abiotic stress. Reporter construct pCambia1301:ProZmHAK1:GUS shows that the ZmHAK1 gene is active in the roots, stems, and leaves. Using yeast one-hybrid experiment, we showed that the ZmHAK1 promoter interacts with the transcription factors ZmRAP2.11 and ZmARF2, and that these interactions occur on different fragments of the ZmHAK1 promoter. Transcription factor ZmRAP2.11 localizes in the nucleus, while ZmARF2 is found both in the nucleus and in the cell cytoplasm. In conclusion, our results suggest that the ZmHAK1 regulation has an important role in the process of absorbing potassium ions, and possibly in the response of maize to abiotic stress.