| Summary: | Potassium (K<sup>+</sup>) deficiency is a key factor limiting maize growth and yield. Auxin plays an important role in maize adaptation to K<sup>+</sup> deficiency, but its physiological and molecular mechanisms are largely unclear. In this study, the exogenous application of 0.01 μmol·L<sup>–1</sup> α-Naphthalene acetic acid (NAA) could effectively alleviate the growth inhibition of maize roots caused by K<sup>+</sup> deficiency, especially in the low-K-sensitive maize inbred line D937. The transcriptome results showed that 3924 and 5458 genes were differentially expressed by exogenous NAA in D937 (sensitive to K<sup>+</sup> deficiency) and 90-21-3 (tolerant to K<sup>+</sup> deficiency) under K<sup>+</sup> deficiency, respectively. The exogenous application of NAA to D937 results in maintenance of the indole acetic acid (IAA) levels by inducing an upregulation in the expression of YUCCA-encoding genes and decreases abscisic acid (ABA) content by inducing the differential expression of genes encoding NCED (downregulated), ABA2 (downregulated), and PP2C (upregulated), thereby reducing growth damage caused by K<sup>+</sup> deficiency. In 90-21-3, exogenous NAA can decrease ABA content and increase IAA/ABA by inducing the differential expression of CYP707- and ABF-related genes, inhibiting the excess accumulation of reactive oxygen species by inducing the differential expression of genes encoding antioxidant enzymes, and maintain cellular K<sup>+</sup> homeostasis by regulating the expression of genes encoding K<sup>+</sup> channels and transporters, thus enhancing plant tolerance to K<sup>+</sup> deficiency. This study lays the foundation for understanding the molecular mechanisms underlying maize adaptation to K<sup>+</sup> deficiency.
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