Phloem specific promoter from a satellite associated with a DNA virus.

DNAbeta is a satellite molecule associated with some monopartite begomoviruses and encodes a single gene (betaC1), which is highly conserved in position and size among DNAbeta molecules. A 955 nt fragment of Tomato yellow leaf curl China virus (TYLCCNV) DNAbeta, upstream of the translation start site of betaC1 gene was tested for its promoter activity with gus as a reporter gene. Analysis of beta-glucuronidase (GUS) activity following transient expression assays indicated that the 955 nt fragment had promoter activity and that 3'-deletions of 399 or 173 nt of the fragment resulted in complete loss of its promoter activity. The 5'-deletions of 782 or 556 nt of the fragment, however, did not affect its activity. Histochemical staining revealed that this fragment can be used to express gus gene specifically in phloem tissue of stably transformed tobacco plants. Further studies have indicated that a 173 nt segment from 3'-end of the 955 nt fragment was responsible for basic promoter activity and phloem-specific expression.