SRPP, a cell-wall protein is involved in development and protection of seeds and root hairs in Arabidopsis thaliana

Abstract

Enhancement of root hair development in response to phosphate (Pi) deficit has been reported extensively. Root hairs are involved in major root functions such as the absorption of water, acquisition of nutrients and secretion of organic acids and enzymes. Individual root hair cells maintain these functions and appropriate structure under various physiological conditions. We carried out a study to identify protein(s) which maintain the structure and function of root hairs, and identified a protein (SEED AND ROOT HAIR PROTECTIVE PROTEIN, SRPP) that was induced in root hairs under Pi-deficient conditions. Promoter assay and mRNA quantification revealed that SRPP was expressed in root hairs and seeds. A knockout mutant, srpp-1, consistently displayed defects in root hairs and seeds. Root hairs in srpp-1 were short and the phenotypes observed under Pi-deficient conditions were also detected in ethylene-treated srpp-1 plants. Propidium iodide stained most root hairs of srpp-1 grown under Pi-deficient conditions, suggesting cell death. In addition to root hairs, most srpp-1 seeds were withered and their embryos were dead. SRPP tagged with green fluorescent protein was detected in the cell wall. Electron microscopy showed abnormal morphology of the cell wall. Wild-type phenotypes were restored when the SRPP gene was expressed in srpp-1. These data strongly suggest that SRPP contributes to the construction of robust cell walls, whereby it plays a key role in the development of root hairs and seeds.

Enhancement of cell wall protein SRPP expression during emergent root hair development in Arabidopsis

“…(2) Two pectin methylesterase genes ( At5g04960 ; RHS12 ), which were listed as RHS genes co-expressed with SRPP in the ATTED-II database, were enhanced by Pi deficiency and suppressed in mutant lines with no or short root hairs. Consistent with a previous report, 7 the present observations suggest that SRPP is involved in the formation of cell walls during emergent root hair development induced by Pi deficiency, but not in root hair differentiation.…”

“…The SRPP protein was not detected in seedlings grown under normal conditions, 7 but SRPP mRNA was detected before Pi depletion treatment ( Fig. 3A ).…”

“…A unique protein, the seed and root hair protective protein (SRPP), was recently identified in the cell walls of root hairs and seeds. 7 The SRPP ( SEED AND ROOT HAIR PROTECTIVE PROTEIN ) gene was identified previously as root hair–specific 13 ( RHS13 ) by microarray analysis. 8 SRPP is highly expressed and the protein was detected in root hairs grown under phosphate (Pi)-deficient conditions.…”

“…SRPP knockout mutants have short, bent root hairs and root hair death as phenotypic properties. 7 SRPP consists of 165 amino-acid residues and is rich in basic residues (pI, 9.21). A protein linked to green fluorescent protein was detected in the cell wall spaces of root hairs.…”

Cell Wall Proteins Play Critical Roles in Plant Adaptation to Phosphorus Deficiency

“…So far, the functions of most CWPs in mediating plant root growth in responses to Pi starvation remain largely unknown, except for a small set of CWPs including expansins, PRPs, and some oxidoreductases [65,66,67,68,69].…”