Characterization of Ricinus communis phloem profilin, RcPRO1

Characterization of Ricinus communis phloem profilin, RcPRO1 The mature, functional sieve tube, which forms the conduit for assimilate distribution in higher plants, is dependent upon protein import from the companion cells for maintenance of the phloem long-distance translocation system. Using antibodies raised against proteins present in the sieve-tube exudate of Ricinus communis (castor bean) seedlings, a cDNA was cloned which encoded a putative profilin, termed RcPRO1. Expression and localization studies indicated that RcPRO1 mRNA encodes a phloem profilin, with some expression occurring in epidermal, cortex, pith and xylem tissue. Purified, recombinant RcPRO1 was functionally equivalent to recombinant maize profilin ZmPRO4 in a live cell nuclear displacement assay. The apparent equilibrium dissociation constant for RcPRO1 binding to plant monomeric (G-)actin was lower than the previously characterized maize profilins. Moreover, the affinity of RcPRO1 for poly-L-proline (PLP) was significantly higher than that for recombinant maize profilins. Within the sieve-tube exudate, profilin was present in 15-fold molar excess to actin. The data suggest that actin filament formation is prevented within the assimilate stream. These results are discussed in terms of the unique physiology of the phloem. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Plant Molecular Biology Springer Journals

Characterization of Ricinus communis phloem profilin, RcPRO1

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Publisher
Springer Journals
Copyright
Copyright © 2000 by Kluwer Academic Publishers
Subject
Life Sciences; Biochemistry, general; Plant Sciences; Plant Pathology
ISSN
0167-4412
eISSN
1573-5028
D.O.I.
10.1023/A:1006391508429
Publisher site
See Article on Publisher Site

Abstract

The mature, functional sieve tube, which forms the conduit for assimilate distribution in higher plants, is dependent upon protein import from the companion cells for maintenance of the phloem long-distance translocation system. Using antibodies raised against proteins present in the sieve-tube exudate of Ricinus communis (castor bean) seedlings, a cDNA was cloned which encoded a putative profilin, termed RcPRO1. Expression and localization studies indicated that RcPRO1 mRNA encodes a phloem profilin, with some expression occurring in epidermal, cortex, pith and xylem tissue. Purified, recombinant RcPRO1 was functionally equivalent to recombinant maize profilin ZmPRO4 in a live cell nuclear displacement assay. The apparent equilibrium dissociation constant for RcPRO1 binding to plant monomeric (G-)actin was lower than the previously characterized maize profilins. Moreover, the affinity of RcPRO1 for poly-L-proline (PLP) was significantly higher than that for recombinant maize profilins. Within the sieve-tube exudate, profilin was present in 15-fold molar excess to actin. The data suggest that actin filament formation is prevented within the assimilate stream. These results are discussed in terms of the unique physiology of the phloem.

Journal

Plant Molecular BiologySpringer Journals

Published: Oct 16, 2004

References

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