TheArabidopsisRoot Hair Cell Wall Formation Mutantlrx1Is Suppressed by Mutations in theRHM1Gene Encoding a UDP-L-Rhamnose Synthase

Abstract

Cell and cell wall growth are mutually dependent processes that must be tightly coordinated and controlled. LRR-extensin1 (LRX1) of Arabidopsis thaliana is a potential regulator of cell wall development, consisting of an N-terminal leucine-rich repeat domain and a C-terminal extensin-like domain typical for structural cell wall proteins. LRX1 is expressed in root hairs, and lrx1 mutant plants develop distorted root hairs that often swell, branch, or collapse. The aberrant cell wall structures found in lrx1 mutants point toward a function of LRX1 during the establishment of the extracellular matrix. To identify genes that are involved in an LRX1-dependent developmental pathway, a suppressor screen was performed on the lrx1 mutant, and two independent rol1 (for repressor of lrx1) alleles were isolated. ROL1 is allelic to Rhamnose Biosynthesis1, which codes for a protein involved in the biosynthesis of rhamnose, a major monosaccharide component of pectin. The rol1 mutations modify the pectic polysaccharide rhamnogalacturonan I and, for one allele, rhamnogalacturonan II. Furthermore, the rol1 mutations cause a change in the expression of a number of cell wall-related genes. Thus, the lrx1 mutant phenotype is likely to be suppressed by changes in pectic polysaccharides or other cell wall components.

Coexpression-Based Clustering of Arabidopsis Root Genes Predicts Functional Modules in Early Phosphate Deficiency Signaling

“…Homozygous mutants form short hairs under Pi-deficient conditions. The gene is closely correlated with LEUCINE-RICH REPEAT (LRR)/ EXTENSIN1 (LRX1), an important regulator of root hair development, and this gene is overexpressed in a lrx1 repressor of lrx1 (rol1) double mutant, together with a set of genes involved in the modification of pectic polysaccharides (Diet et al, 2006), suggesting a function of At3g01730 in pectin-related processes. Interestingly, in lrx1 rol1 plants, the length of primary roots, root hairs, and the longitudinal length of trichoblasts are affected, traits that are typically changed in Pideficient plants.…”

Comprehensive Flavonol Profiling and Transcriptome Coexpression Analysis Leading to Decoding Gene–Metabolite Correlations inArabidopsis

“…The mutants ugt75c1,ugt78d1,ugt78d2,ugt89c1,, and rhm2-1 were described previously (Jones et al, 2003;Usadel et al, 2004;Tohge et al, 2005;Diet et al, 2006;Yonekura-Sakakibara et al, 2007). The T-DNA-inserted knockout mutants of omt1 (CS25167) and tt7 (CS6509) were obtained from the ABRC.…”

7-Rhamnosylated Flavonols Modulate Homeostasis of the Plant Hormone Auxin and Affect Plant Development

“…rol1-2 seedlings are characterized by shorter roots and root hairs than in the wild type. The rol1-2 seedling shoot develops deformed trichomes and hyponastic cotyledons with brick-shaped pavement cells, whereas the wild type develops regular trichomes and epinastic cotyledons with puzzle-shaped jigsaw-like pavement cells (30,43). There is no obvious growth defect detectable in rol1-2 adult plants, presumably due to the functional redundancy among the three RHM genes (45).…”

“…The rol1-2 mutant was identified in a screen for alterations in cell wall structures and shows modifications in the Rha-rich cell wall component pectin (43). In addition, rol1-2 also shows changes in the flavonol glycosylation profile, mainly a reduction in the degree of rhamnosylation, whereas the overall quantity of flavonols is not affected (30,44).…”

“…The rol1-2 (repressor of lrx1) mutant is affected in one of three RHM genes, RHM1, encoding rhamnose synthase, which converts UDP-Glc to UDP-Rha (43). The rol1-2 mutant was identified in a screen for alterations in cell wall structures and shows modifications in the Rha-rich cell wall component pectin (43).…”