Members of the legume genus Lupinus exude phloem ‘spontaneously’ from incisions made to the
vasculature. This feature was exploited to document macromolecules present in exudate of white lupin (Lupinus
albus [L.] cv Kiev mutant), in particular to identify proteins and RNA molecules, including microRNA (miRNA). Proteomic analysis tentatively identified 86 proteins from 130 spots collected from 2D gels analysed by partial amino acid sequence determination using MS/MS. Analysis of a cDNA library constructed from exudate
identified 609 unique transcripts. Both proteins and transcripts were classified into functional groups. The largest
group of proteins comprised those involved in metabolism (24%), followed by protein modification/turnover (9%),
redox regulation (8%), cell structural components (6%), stress and defence response (6%) with fewer in other
groups. More prominent proteins were cyclophilin, ubiquitin, a glycine-rich RNA-binding protein, a group of
proteins that comprise a glutathione/ascorbate-based mechanism to scavenge oxygen radicals, enzymes of
glycolysis and other metabolism including methionine and ethylene synthesis. Potential signalling macromolecules
such as transcripts encoding proteins mediating calcium level and the Flowering locus T (FT) protein were also
identified. From around 330 small RNA clones (18-25 nt) 12 were identified as probable miRNAs by homology with
those from other species. miRNA composition of exudate varied with site of collection (e.g. upward versus
downward translocation streams) and nutrition (e.g. phosphorus level). This is the first inventory of macromolecule composition of phloem exudate from a species in the Fabaceae, providing a basis to identify systemic signalling macromolecules with potential roles in regulating development, growth and stress response of legumes.
