The Potassium-Dependent Transcriptome Analysis of Maize Provides Novel Insights into the Rescue Role of Auxin in Responses to Potassium Deficiency

Potassium (K⁺) deficiency is a key factor limiting maize growth and yield. Auxin plays an important role in maize adaptation to K⁺ deficiency, but its physiological and molecular mechanisms are largely unclear. In this study, the exogenous application of 0.01 μmol·L^–1 α-Naphthalene acetic acid (NAA) could effectively alleviate the growth inhibition of maize roots caused by K⁺ 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⁺ deficiency) and 90-21-3 (tolerant to K⁺ deficiency) under K⁺ 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⁺ 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⁺ homeostasis by regulating the expression of genes encoding K⁺ channels and transporters, thus enhancing plant tolerance to K⁺ deficiency. This study lays the foundation for understanding the molecular mechanisms underlying maize adaptation to K⁺ deficiency.