Functional characterization of the root-specific promoter of RcbHLH120 in Rosa chinensis and its ABA response properties

To elucidate the spatiotemporal expression and hormonal responsiveness of the bHLH transcription factor RcbHLH120 and its native promoter, and to provide a theoretical basis for root-targeted stress-resistance breeding in rose.

R. chinensis ‘Old Blush’ was used as material. The RcbHLH120 (GenBank: PP358758) and its 1.2 kb promoter sequence proRcbHLH120 (GenBank: PP358763) were cloned. Spatiotemporal expression profiles were determined by qRT-PCR, cis-acting elements were predicted in silico, and the binary vector pBI121-proRcbHLH120::GUS was constructed and introduced into Arabidopsis thaliana. Promoter activity was subsequently verified through histochemical GUS staining, GUS protein activity assay and quantitative analyses under exogenous ABA treatment.

RcbHLH120 encodes 306 amino acids, and its mRNA is specifically enriched in the root of rose. The promoter proRcbHLH120 contains 19 root-specific cis-elements (including OSE1ROOTNODULE, ROOTMOTIFTAPOX1, etc.) and one ABA response element ABRE. Heterologous transformation assays revealed that proRcbHLH120 drives the specific expression of the gus gene in the roots of transgenic Arabidopsis, and the GUS protein activity in the roots significantly increased after exogenous ABA treatment compared to the wild type, confirming the promoter's dual functions of root tissue specificity and ABA induction.

This study identified the first root-specific bHLH transcription factor RcbHLH120 in Rosa chinensis and found that its promoter proRcbHLH120 integrated multiple cis-elements to orchestrate root-restricted expression and ABA responsiveness, the promoter can be used as a versatile tool for spatiotemporally precise and stress-inducible root engineering.