Identification and Expression Profiling of the Cytokinin Synthesis Gene Family IPT in Maize

Isopentyltransferase (<i>IPT</i>) is a key rate-limiting enzyme in cytokinin synthesis, playing a crucial role in plant growth, development, and response to adverse conditions. Although the IPT gene family has been studied in various plants, comprehensive identification and functional characterization of <i>IPT</i> genes in maize (<i>Zea mays</i>) remain underexplored. In this study, ten <i>IPT</i> gene family members (<i>ZmIPT1</i>-<i>ZmIPT10</i>) were identified in the maize genome, and their gene structure, physicochemical properties, evolutionary relationships, expression patterns, and stress response characteristics were systematically analyzed. The <i>ZmIPT</i> genes were found to be unevenly distributed across six chromosomes, with most proteins predicted to be basic and localized primarily in chloroplasts. Phylogenetic analysis grouped the <i>ZmIPT</i> family into four subfamilies, showing close evolutionary relationships with rice IPT genes. Conserved motif and gene structure analyses indicated that the family members were structurally conserved, with five collinear gene pairs being identified. Ka/Ks analysis revealed that these gene pairs underwent strong purifying selection during evolution.Cis-element analysis of promoter regions suggested that <i>ZmIPT</i> genes are widely involved in hormone signaling and abiotic stress responses. Tissue-specific expression profiling showed that <i>ZmIPT5</i>, <i>ZmIPT7</i>, and <i>ZmIPT8</i> were highly expressed in roots, with <i>ZmIPT5</i> exhibiting consistently high expression under multiple abiotic stresses. qRT-PCR validation confirmed that <i>ZmIPT5</i> expression peaked at 24 h after stress treatment, indicating its key role in long-term stress adaptation. Protein interaction analysis further revealed potential interactions between <i>ZmIPT5</i> and cytokinin oxidases (<i>CKX1</i>, <i>CKX5</i>), as well as FPP/GGPP synthase family proteins, suggesting a regulatory role in cytokinin homeostasis and stress adaptation. Overall, this study provides comprehensive insights into the structure and function of the <i>ZmIPT</i> gene family and identifies <i>ZmIPT5</i> as a promising candidate for improving stress tolerance in maize through molecular breeding.