Transcriptomic analysis of interstock-induced dwarfism in Sweet Persimmon (Diospyros kaki Thunb.)

Abstract

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'/<i>Diospyros lotus</i> and 'Kanshu'/'Nantong-xiaofangshi'/<i>Diospyros lotus</i>) 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 <i>AUX/IAA</i> and auxin-responsive <i>GH3</i> genes was enhanced in scions grafted on the interstock and was negatively correlated with the IAA content and growth of scions. The expression of <i>GA2ox</i>, <i>DELLA</i>, and <i>SPINDLY</i> genes were also upregulated and associated with a decrease in the level of GA in scions grafted on the interstock. Since one of the <i>GA2ox</i> unigenes was annotated as <i>DkGA2ox1</i> in <i>Diospyros kaki</i>, but was not functionally validated, a functional analysis was conducted in transgenic tobacco. Overexpression of <i>DkGA2ox1</i> 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.