THE PLANT CELL, Vol 6, Issue 9 1265-1275, Copyright © 1994 by American Society of Plant Biologists
A New Proline-Rich Early Nodulin from Medicago truncatula Is Highly Expressed in Nodule Meristematic Cells
R. C. Wilson, F. Long, E. M. Maruoka and J. B. Cooper
Department of Biological Sciences, University of California, Santa Barbara, California 93105
We cloned and characterized MtPRP4, a new member of the repetitive
proline-rich protein gene family in Medicago truncatula. The sequence of
MtPRP4 predicts a 62-kD protein consisting of a 22-amino acid N-terminal
signal peptide and a 527-amino acid repetitive proline-rich domain composed
of three repetitive pentapeptide motifs arranged into two decapeptide
repeats: PPVEKPPVHK and PPVEKPPVYK. MtPRP4 is the largest PRP described to
date and contains repeated motifs that have not previously been found
together in a single polypeptide. RNA gel blot experiments detected MtPRP4
transcripts in symbiotic root nodules, but not in roots, hypocotyls, or
leaves. Accumulation of MtPRP4 transcript was an early response to
Rhizobium inoculation and did not depend on nodule infection. In situ
hybridization experiments demonstrated that MtPRP4 was expressed early in
the development of the nodule meristem and that expression was highest in
the meristematic cells of mature indeterminate nodules. These data support
the proposition that an important early response of legume host roots to
Rhizobium involves remodeling the host extracellular matrix and that
proline-rich wall proteins play an important role in this architectural
modification.
