Combined metabolomic and genetic approaches reveal a link between the polyamine pathway and albumin 2 in developing pea seeds.

Helene Vigeolas,Claire Domoney,Catherine Chinoy,Bernard Blessington,Peter Geigenberger,Ellen Zuther

doi:10.1104/pp.107.111369

Abstract

Several legume seed proteins that are potentially allergenic, poorly digested by farm animals, and/or have undesirable functional properties, have been described. One of these is the albumin protein in pea (Pisum sativum) called PA2. A naturally occurring mutant line that lacks PA2 has been exploited in studies to determine the biological function of this nonstorage protein in seed development. The mutant, which has a small seed, a tall plant phenotype, and lacks most of the PA2-encoding genes, has been crossed with a standard cultivar, 'Birte,' which contains PA2 to give rise to a recombinant inbred (RI) population. An F(3) line carrying the mutation and having a short plant phenotype has been used to generate backcross (BC) lines with 'Birte.' Despite having a lower albumin content, seeds from the mutant parent and RI lines lacking PA2 have an equivalent or higher seed nitrogen content. Metabolite profiling of seeds revealed major differences in amino acid composition and polyamine content in the two parent lines. This was investigated further in BC lines, where the effects of differences in seed size and plant height between the two parents were eliminated. Here, differences in polyamine synthesis were maintained as was a difference in total seed protein between the BC line lacking PA2 and 'Birte.' Analysis of enzyme activities in the pathways of polyamine synthesis revealed that the differences in spermidine content were attributable to changes in the overall activities of spermidine synthase and arginine decarboxylase. Although the genes encoding spermidine synthase and PA2 both localized to the pea linkage group I, the two loci were shown not to be closely linked and to have recombined in the BC lines. A distinct locus on linkage group III contains a gene that is related to PA2 but expressed predominantly in flowers. The results provide evidence for a role of PA2 in regulating polyamine metabolism, which has important functions in development, metabolism, and stress responses in plants.

Highlights

Several legume seed proteins that are potentially allergenic, poorly digested by farm animals, and/or have undesirable functional properties, have been described
The results indicate that metabolic changes occur in the polyamine pathway with altered amounts of spermidine in the PA2-deficient parent and backcross (BC) mutant lines compared with ‘Birte.’ Polyamines have been implicated in a wide range of biological processes in plants, including growth, development, and stress responses; the regulation of their metabolism is still unknown (Kumar et al, 1997)
One recombinant inbred (RI) line (RIL; le) was selected to introgress the PA2 mutation into ‘Birte.’ A DNA marker was developed to follow the mutation in RI and BC lines (Fig. 1, A–C)

Summary

Introduction

Several legume seed proteins that are potentially allergenic, poorly digested by farm animals, and/or have undesirable functional properties, have been described. RIL pools showed that lines lacking PA2 have an elevated N content compared with those that contain PA2 in both Le and le backgrounds (Fig. 2A), suggesting a compensatory increase in other seed proteins in the mutant background.

Results

Conclusion