PpIBH1-1 limits internode elongation of peach shoot in a dose-dependent manner

Peach [Prunus persica (L.) Batsch] annual shoots grow up quickly, which limits the lighting and ventilation of an orchard. Atypical bHLH proteins IBH1(INCREASED LEAF INCLINATION1 BINDING bHLH1) play substantial roles in regulating cell elongation and plant stature. In this study, three PpIBH1s (PpIBH1-1/-2/-3) were identified in peach genome and contain a conserved AS domain and a characteristic HLH domain. The transcript levels of three PpIBH1s positively correlated with internode length, which gradually increased from apex to base along the peach shoots. This positive correlation was further confirmed in apple and poplar shoots. And the PpIBH1s gene were highly expressed in the shoot tips collected from twelve dwarf peach cultivars (gid1c mutants). In tissue-specific expression analysis, PpIBH1-1 are more highly expressed in tissues at the growth-arrested stage than cell-elongating. Transgenic Arabidopsis lines showed that different plant heights depending on the dose of PpIBH1-1 transcripts. And the dwarfing PpIBH1-1 transgenic lines were caused by the shorted cell length. PpIBH1-1 interacted with two bHLH factors (PpACE2 and PpLP1). These results suggested that PpIBH1-1 probably prevents internode elongation of peach shoots in a dose-dependent manner. Our work provided a foundation for properly controlling the growth of annual peach branches.