Genome-wide identification and characterization of the IPT family members in nine Rosaceae species and a functional analysis of MdIPT5b in cold resistance

Cytokinins are members of a group of phytohormones involved in various growth and developmental processes in plants.Isopentenyl transferase(IPT)is the rate-limiting enzyme in catalyzing the biosynthesis of cytokinins.In this study,to understand the role of IPT family in cold resistance,78 IPT candidates were identified and characterized in nine Rosaceae genomes.The expansion of IPT families in the Rosaceae primarily occurred through segmental duplication rather than tandem duplication.In general,purifying selection controlled the evolution of IPT families in the Rosaceae,with IPT3 and IPT5 homologs as the primary drivers of evolution.Cis-elements,which are involved in the re-sponses to many environmental stresses or phytohormone signals,were identified in the promoters of MdIPT members.This was consistent with the trends of expression of the MdIPT genes in apple(Malus domestica)calli.MdIPT5b was also found to exhibit multiple responses to phytohormones and stress signals.The ectopic expression of MdIPT5b resulted in an increase in cold resistance in transformed apple calli and tomato(Solanum lycopersicum)plantlets.The redox balance was partially stabilized through the accumulation of proline under cold stress.However,the ascorbate-glutathione cycle cannot be stabilized in the cold.All physiological and biochemical assays are preformed in spec-trophotometer.These results showed that regulating the expression of IPT genes for moderate cytokinin improvement could enhance the accumulation of proline to stabilize the osmotic and redox balances to improve resistance to cold stress.