Abstract: For screening phloem-specific promoters in citrus，the plant expression vectors containing
GUS reporter cassette driven by Glycine-rich protein gene promoter （GRP）from Vigna unguiculata（Linn.）
Walp（bean），Agrobacterium Rhizogenes RolC gene promoter（Rolc）from Agrobacterium rhizogenes and
Sucrose synthase 1 gene（RSSl）promoter from Oryza sativa（rice）were constructed，and introduced into
the Poncirus trifoliata（L.）Raf. seedling epicotyls by Agrobacterium-mediated transformation.
Histochemical β-glucuronidase（GUS）analysis revealed vascular-specific expression of the GUS protein in
citrus. The GRP promoter displayed strong and strict phloem-specific expression pattern in this study while
the RSS1 promoter could drive low levels of GUS gene expression in citrus. Strong constitutive expression of GUS driven by the Rolc promoter was detected in root and stem. These results were further confirmed
by reverse transcription real-time polymerase chain reaction and quantitative GUS enzyme activity assays.
The strong vascular-specific promoter i.e. GRP promoter provides a good candidate for targeting
expression of antibacterial constructs to battle Citrus huanglongbing disease（HLB or citrus greening
disease），associated with a phloem-limited Gram-negative bacterium

Key words: Poncirus trifoliata, phloem-specificity promoter, genetic transformation, GUS