Growth monitoring indicated that the height of ‘Kanshu’ plants with ‘Nantong-xiaofangshi’ as an interstock was significantly shorter than that of ‘Kanshu’ plants with no interstock. A transcriptome analysis of the two graft combinations (‘Kanshu’/Diospyros lotus and ‘Kanshu’/‘Nantong-xiaofangshi’/Diospyros lotus) was conducted to explore the dwarfing genes related to the use of the ‘Nantong-xiaofangshi’ interstock. Hormone levels and water conductance were also measured in these two graft combinations. The results indicated that the levels of both IAA and GA were lower in ‘Kanshu’ that had been grafted onto the ‘Nantong-xiaofangshi’ interstock than in ‘Kanshu’ with no interstock; additionally, the water conductance was lower in grafts with interstocks than in grafts without interstocks. The expression of AUX/IAA and auxin-responsive GH3 genes was enhanced in scions grafted on the interstock and was negatively correlated with the IAA content and growth of scions. The expression of GA2ox, DELLA, and SPINDLY genes were also upregulated and associated with a decrease in the level of GA in scions grafted on the interstock. Since one of the GA2ox unigenes was annotated as DkGA2ox1 in Diospyros kaki, but was not functionally validated, a functional analysis was conducted in transgenic tobacco. Overexpression of DkGA2ox1 in transgenic plants resulted in a dwarf phenotype that could be recovered by the exogenous application of GA₃. We conclude that the ‘Nantong-xiaofangshi’ interstock affects the water conductance and expression of genes related to the metabolism and transduction of IAA and GA in the grafted scion and thus regulates phytohormone levels, producing dwarfing.

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