Hybrid proline-rich proteins: novel players in plant cell elongation?
OBJECTIVE
Hybrid proline-rich proteins (HyPRPs) represent a large family of putative cell-wall proteins characterized by the presence of a variable N-terminal domain and a conserved C-terminal domain that is related to non-specific lipid transfer proteins. The function of HyPRPs remains unclear, but their widespread occurrence and abundant expression patterns indicate that they may be involved in a basic cellular process.


METHODS
To elucidate the cellular function of HyPRPs, we modulated the expression of three HyPRP genes in tobacco (Nicotiana tabacum) BY-2 cell lines and in potato (Solanum tuberosum) plants.


RESULTS
In BY-2 lines, over-expression of the three HyPRP genes with different types of N-terminal domains resulted in similar phenotypic changes, namely increased cell elongation, both in suspension culture and on solid media where the over-expression resulted in enhanced calli size. The over-expressing cells showed increased plasmolysis in a hypertonic mannitol solution and accelerated rate of protoplast release, suggesting loosening of the cell walls. In contrast to BY-2 lines, no phenotypic changes were observed in potato plants over-expressing the same or analogous HyPRP genes, presumably due to more complex compensatory mechanisms in planta.


CONCLUSIONS
Based on the results from BY-2 lines, we propose that HyPRPs, more specifically their C-terminal domains, represent a novel group of proteins involved in cell expansion.
Charles University in Prague, Faculty of Science, Department of Experimental Plant Biology, Czech Republic.
Lenka
L
Dvoráková
Miroslav
M
Srba
Zdenek
Z
Opatrny
Lukas
L
Fischer
D049108:Cell Enlargement; D049109:Cell Proliferation; D002473:Cell Wall / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D059828:Plant Cells / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011392:Proline / Q000378:metabolism*; D055232:Proline-Rich Protein Domains; D011198:Solanum tuberosum / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D014026:Nicotiana / Q000166:cytology / Q000235:genetics / Q000378:metabolism
D010940:Plant Proteins; D011392:Proline