Small Cyclic Amphipathic Peptides (SCAmpPs) genes in citrus provide promising tools for more effective tissue specific transgenic expression
A gene family of Small Cyclic Amphipathic Peptides (SCAmpPs) has been identified in citrus. The citrus genomes include 100-150 SCAmpPs genes, and ~50 are represented in the citrus EST database. These genes encode small ~50 residue precursor proteins that are post-translationally processed, releasing 5-10 residue cyclic peptides. The SCAmpPs genes structures are highly conserved, with the small coding domains interrupted by a single intron and relatively extended untranslated regions. Some family members are very highly transcribed in specific tissues, as determined by representation in tissue-specific cDNA libraries, with specificity identified in phloem, root, and ovary tissue. Thus far, the function of SCAmpPs remains undetermined, though their structures are consistent with membrane binding and K+ ionophore function has been identified through LC-MS-MS. High concentrations of phloem-specific SCAmpPs have been verified in citrus tissues using LC-MS. Remarkably, even though the final predicted peptide sequences of the phloem SCAmpPs are quite variable, there is almost complete identity in the promoter, first exon and intron. Constructs using phloem, root and ovary SCAmpPs' transcriptional control sequences have been used to express GUS reporter genes in Arabidopsis and Citrus. Reporter gene expression matched the predicted tissue-specific profiles from the individual SCAmpPs ESTs. Previously studied tissue-specific promoters have provided only modest expression, and it appears that SCAmpPs promoters will provide much greater expression with strong tissue specificity. Studies are underway to determine the function of upstream SCAmpPs sequence and value of SCAmpPs promoter/sequence in high phloem expression of anti-microbial peptides for control of phloem-limited bacteria.
Belknap, W.R., Thomson, J., Thilmony, R., McCue, K.F., Hao, G. and Stover, E. 2017. Small Cyclic Amphipathic Peptides (SCAmpPs) genes in citrus provide promising tools for more effective tissue specific transgenic expression. Acta Hort. (ISHS) 1172:85-90
breeding, Huanglonging, HLB, ovule specific, phloem specific, root specific