Macromolecular composition of phloem exudate from white lupin (Lupinus albusL.)

Caren Rodriguez-Medina,Craig A Atkins,Megan E Jordan,Penelope Mc Smith,Anthea J Mann

doi:10.1186/1471-2229-11-36

Caren Rodriguez-Medina, Craig A Atkins + Show 3 more

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https://doi.org/10.1186/1471-2229-11-36

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Abstract

BackgroundMembers 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).ResultsProteomic 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).ConclusionsThis 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.

Highlights

Members of the legume genus Lupinus exude phloem ‘spontaneously’ from incisions made to the vasculature
Proteomic analyses of phloem exudates collected from incisions to the vasculature of a number of species that either ‘bleed’ spontaneously, or, in which exudation is aided by application of a chelator have shown a broad range of proteins, a small number of which are common with those identified in phloem exudate collected by stylectomy [9]
Additional file 2 shows the full list of identified proteins as well as the partial amino acid sequences used for identification and the BLAST search results

Summary

Introduction

Members of the legume genus Lupinus exude phloem ‘spontaneously’ from incisions made to the vasculature. It is generally believed that the enucleate SE has lost the Proteomic analyses of phloem exudates collected from incisions to the vasculature of a number of species that either ‘bleed’ spontaneously (e.g. castor bean [5], cucurbits [6,7] and Brassica napus [8]), or, in which exudation is aided by application of a chelator have shown a broad range of proteins, a small number of which are common with those identified in phloem exudate collected by stylectomy [9] While together these data indicate that the phloem stream contains many proteins, it is not clear which of these are translocated and, more importantly, which have a function dependent on their long distance transport

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