Genome-wide identification and functional characterization of Isopentenyl Transferase (IPT) genes in mulberry (Morus...

Cytokinins (CKs) orchestrate a myriad of developmental and adaptive processes in plants, with their biosynthesis initiated by isopentenyl transferases (IPTs), the key enzymes catalyzing the first and rate-limiting step. Although indispensable for cytokinin biosynthesis, IPTs remain poorly characterized in Morus species. Here, we performed a genome-wide identification and comparative analysis of the IPT gene family in Morus notabilis, Morus alba, and Morus indica cv. K2. Six IPT loci were identified in M. notabilis and M. alba, whereas seven were found in M. indica. Phylogenetic reconstruction and structure analyses classified them into adenylate-type IPTs (Ad-IPTs) and tRNA-derived IPTs (tRNA-IPTs). Ad-IPTs are intronless and exhibit discrete, tissue-specific expression, whereas tRNA-IPTs contain multiple introns and display constitutive transcription, reflecting divergent evolutionary trajectories. Expression profiling revealed strong induction of Ad-IPTs by cytokinin and auxin, and marked up-regulation under drought, while tRNA-IPTs were transcriptionally repressed, implicating functional partitioning in cytokinin homeostasis under environmental constraints. Subcellular localization demonstrated MiIPT1 colocalization with a CFP-tagged plastid marker, confirming its plastid localization. Collectively, these findings provide the first integrative characterization of IPTs in mulberry, delineating lineage-specific diversification and stress-responsive regulation, and identify promising genetic targets for enhancing growth and drought resilience in perennial crops.