The Modified Flavonol Glycosylation Profile in the Arabidopsis rol1 Mutants Results in Alterations in Plant Growth and Cell Shape Formation

Abstract

Flavonoids are secondary metabolites known to modulate plant growth and development. A primary function of flavonols, a subgroup of flavonoids, is thought to be the modification of auxin fluxes in the plant. Flavonols in the cell are glycosylated, and the repressor of lrx1 (rol1) mutants of Arabidopsis thaliana, affected in rhamnose biosynthesis, have a modified flavonol glycosylation profile. A detailed analysis of the rol1-2 allele revealed hyponastic growth, aberrant pavement cell and stomatal morphology in cotyledons, and defective trichome formation. Blocking flavonoid biosynthesis suppresses the rol1-2 shoot phenotype, suggesting that it is induced by the modified flavonol profile. The hyponastic cotyledons of rol1-2 are likely to be the result of a flavonol-induced increase in auxin concentration. By contrast, the pavement cell, stomata, and trichome formation phenotypes appear not to be induced by the modified auxin distribution. Together, these results suggest that changes in the composition of flavonols can have a tremendous impact on plant development through both auxininduced and auxin-independent processes.

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

“…In fact, major six flavonol contents in flowers are ;10-to 70-fold higher than in leaves (YonekuraSakakibara et al, 2007). The role of RHM1 for UDP-rhamnose supply to flavonols was also supported by a recent report with young shoots of the rol1 mutants (Ringli et al, 2008) and our data with RHM1 knockdown mutants (SALK_027926 and SALK_143589; see Supplemental Figure 4 online).…”

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

“…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). This confirms the importance of RHM1, which is coexpressed with genes important for flavonol biosynthesis (26) and for flavonol glycosylation.…”

“…In vitro experiments show activity of flavonol aglycones, suggesting that these are the compounds active in modulating polar auxin transport (10,17,18,20). However, the identification of mutant phenotypes induced by changes in the flavonol glycosylation profile suggests function for at least some flavonol glycosides (30,31).…”

“…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).…”

Auxin and Ethylene Induce Flavonol Accumulation through Distinct Transcriptional Networks

“…Interestingly, preliminary analyses of acropetal transport with the alleles described here showed that the tt4-2 and tt7-2 phenotypes are not equivalent, with tt7-2 showing an intermediate phenotype between the wild type and tt4-2 (data not shown). Furthermore, kaempferol and its derivatives have been shown to have distinct developmental roles in leaves based on analysis of the rol1-3 mutant, which is defective in Rha biosynthesis and flavonoid glycosylation (Ringli et al, 2008). This suggests that, in other tissues and auxin transport streams, kaempferol and its derivatives may have a distinct function.…”