Insight into the early steps of root hair formation revealed by the procuste1 cellulose synthase mutant of Arabidopsis thaliana.
BACKGROUND
Formation of plant root hairs originating from epidermal cells involves selection of a polar initiation site and production of an initial hair bulge which requires local cell wall loosening. In Arabidopsis the polar initiation site is located towards the basal end of epidermal cells. However little is currently understood about the mechanism for the selection of the hair initiation site or the mechanism by which localised hair outgrowth is achieved. The Arabidopsis procuste1 (prc1-1) cellulose synthase mutant was studied in order to investigate the role of the cell wall loosening during the early stages of hair formation.


RESULTS
The prc1-1 mutant exhibits uncontrolled, preferential bulging of trichoblast cells coupled with mislocalised hair positioning. Combining the prc1-1 mutant with root hair defective6-1 (rhd6-1), which on its own is almost completely devoid of root hairs results in a significant restoration of root hair formation. The pEXPANSIN7::GFP (pEXP7::GFP) marker which is specifically expressed in trichoblast cell files of wild-type roots, is absent in the rhd6-1 mutant. However, pEXP7::GFP expression in the rhd6-1/prc1-1 double mutant is restored in a subset of epidermal cells which have either formed a root hair or exhibit a bulged phenotype consistent with a function for EXP7 during the early stages of hair formation.


CONCLUSIONS
These results show that RHD6 acts upstream of the normal cell wall loosening event which involves EXP7 expression and that in the absence of a functional RHD6 the loosening and accompanying EXP7 expression is blocked. In the prc1-1 mutant background, the requirement for RHD6 during hair initiation is reduced which may result from a weaker cell wall structure mimicking the cell wall loosening events during hair formation.
Singh
Sunil K
SK
Department of Forest Genetics and Plant Physiology, SLU, 901 83 Umeå, Sweden. Sunil.Kumar.Singh@plantphys.umu.se
Fischer
Urs
U
Singh
Manoj
M
Grebe
Markus
M
Marchant
Alan
A
D017360:Arabidopsis / Q000166:cytology / Q000196:embryology* / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism; D016764:Cell Polarity / Q000187:drug effects; D005030:Ethylenes / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005964:Glucosyltransferases / Q000235:genetics / Q000378:metabolism*; D005966:Glucuronidase / Q000378:metabolism; D009154:Mutation / Q000235:genetics*; D019441:Plant Epidermis / Q000166:cytology / Q000187:drug effects; D018517:Plant Roots / Q000166:cytology / Q000187:drug effects / Q000196:embryology* / Q000201:enzymology; D011401:Promoter Regions, Genetic / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects
D029681:Arabidopsis Proteins; D051792:Basic Helix-Loop-Helix Proteins; D005030:Ethylenes; D019204:GTP-Binding Proteins; D005964:Glucosyltransferases; D005966:Glucuronidase; C472142:AtEXP7 protein, Arabidopsis; C520580:RHD6 protein, Arabidopsis; C036216:ethylene; C457769:PRC1 protein, Arabidopsis; C478648:cellulose synthase