Abstract
The biological function of sterol glucosides (SGs), the most abundant sterol derivatives in higher plants, remains uncertain. In an effort to improve our understanding of these membrane lipids we examined phenotypes exhibited by the roots of Arabidopsis (Arabidopsis thaliana) lines carrying insertions in the UDP-Glc:sterol glucosyltransferase genes, UGT80A2 and UGT80B1. We show that although ugt80A2 mutants exhibit significantly lower levels of total SGs they are morphologically indistinguishable from wild-type plants. In contrast, the roots of ugt80B1 mutants are only deficient in stigmasteryl glucosides but exhibit a significant reduction in root hairs. Sub-cellular investigations reveal that the plasma membrane cell fate regulator, SCRAMBLED (SCM), is mislocalized in ugt80B1 mutants, underscoring the aberrant root epidermal cell patterning. Live imaging of roots indicates that SCM:GFP is localized to the cytoplasm in a non cell type dependent manner instead of the hair (H) cell plasma membrane in these mutants. In addition, we provide evidence for the localization of the UGT80B1 enzyme in the plasma membrane. These data lend further support to the notion that deficiencies in specific SGs are sufficient to disrupt normal cell function and point to a possible role for SGs in cargo transport and/or protein targeting to the plasma membrane.
Highlights
Among various sterol derivatives, the most abundant are steryl glucosides (SGs)[9,10,11,12]
The resulting profile for wild type roots was ~76% sitosteryl, ~13% campesteryl, ~10% stigmasteryl, ~0.4% brassicasteryl and ~0.1% cholesteryl glucosides, a profile similar to that observed in seeds16, 25. fk-J3158 mutants displayed a reduction in total SGs (58% of wild type levels), with significant decreases in both sitosteryl and campesteryl glucosides (~54% and ~44% of the wild type levels, respectively) (Fig. 1A; Supplementary Table S1)
There was a trend indicating a reduction in stigmasteryl glucosides in this mutant
Summary
The most abundant are steryl glucosides (SGs)[9,10,11,12]. While UGT80A2 appears to be responsible for the generation of the bulk of the SGs in aerial tissue and seeds, it is ugt80B1 mutants (and double mutants) that exhibit striking morphological phenotypes[15, 16]. In their 2009 study, DeBolt et al.[15] showed that ugt80B1 single mutants and ugt80A2,ugt80B1 double mutants exhibit growth defects during embryogenesis. In H cells, the expression of WER is inhibited, allowing CPC/TRY/ETC to form a transcriptional regulatory complex with GL3/EGL3/MYC1 and TTG This leaves RHD6 uninhibited, positively regulating H cell differentiation genes
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