The UGT73C5 of Arabidopsis thaliana glucosylates brassinosteroids

Abstract

Steroid hormones are essential for development, and the precise control of their homeostasis is a prerequisite for normal growth. UDP-glycosyltransferases (UGTs) are considered to play an important regulatory role in the activity of steroids in mammals and insects. This study provides an indication that a UGT accepting plant steroids as substrates functions in brassinosteroid (BR) homeostasis. The UGT73C5 of Arabidopsis thaliana catalyses 23-Oglucosylation of the BRs brassinolide (BL) and castasterone. Transgenic plants overexpressing UGT73C5 displayed BR-deficient phenotypes and contained reduced amounts of BRs. The phenotype, which was already apparent in seedlings, could be rescued by application of BR. In feeding experiments with BL, wild-type seedlings converted BL to the 23-O-glucoside; in the transgenic lines silenced in UGT73C5 expression, no 23-O-glucoside was detected, implying that this UGT is the only enzyme that catalyzes BL-23-O-glucosylation in seedlings. Plant lines in which UGT73C5 expression was altered also displayed hypocotyl phenotypes previously described for seedlings in which BR inactivation by hydroxylation was changed. These data support the hypothesis that 23-O-glucosylation of BL is a function of UGT73C5 in planta, and that glucosylation regulates BR activity.glucosylation ͉ glycosyltransferase ͉ homeostasis ͉ plant ͉ steroid

TheArabidopsisC2H2 Zinc Finger INDETERMINATE DOMAIN1/ENHYDROUS Promotes the Transition to Germination by Regulating Light and Hormonal Signaling during Seed Maturation

“…In RAB18:ENY imbibed seeds, both BAS1 and SOB7 were downregulated, consistent with ENY being a promoter of growth, in this case via BRs. BRs are also inactivated by glucosylation through the DOGT1 gene product (Poppenberger et al, 2005), which was downregulated in RAB18: ENY seeds. However, the biosynthetic gene BRASSINOSTE-ROID-6-OXIDASE2 (BR6ox2), which catalyzes the last committed steps to active brassinolide, was also downregulated in RAB18: ENY imbibed seeds; however, this could be the result of feedback inhibition.…”

Functional genomics of family 1 glycosyltransferases in Arabidopsis

“…For example, UGT73C6 (At2g36790) cross hybridized with the adjacent UGT73C5 (At2g36800). UGT73C6 is a flavonol 7-O-glucosyltransferase (Jones et al 2003) while UGT73C5 is a brassinosteroid glucosyltransferase (Poppenberger et al 2005). None of the flavonoid biosynthetic genes had correlation coefficients greater than 0.4 against UGT73C6 probably due to cross hybridization with these two genes.…”

The Arabidopsis geneATST4ais not a typical brassinosteroids catabolic gene

“…[11][12][13][14] Genetic analyses of knockout or knockdown mutants of most of these BR catabolic genes show a reduction in hypocotyl-elongation inhibition in white light in Arabidopsis seedlings. 1,3,6,7,9 The knockout or knockdown approach may in some cases fail to provide any evidence of involvement in BR catabolism due to genetic redundancy or yet other unknown reasons. 6 In vivo and in vitro biochemical assays of the enzymes encoded by some of these genes were also used to confirm their role in BR catabolism.…”

“…In all cases, in planta overexpression of BR catabolic genes leads to characteristic BR-deficient phenotypes at both seedling and adult stages of Arabidopsis. [1][2][3][4][5][6][7][8][9][10] These BR-deficient phenotypes typified by a BR biosynthetic mutant de-etiolated 2-1 (det2-1), include small organ size, small round and dark green leaves, and delayed flowering. [11][12][13][14] Genetic analyses of knockout or knockdown mutants of most of these BR catabolic genes show a reduction in hypocotyl-elongation inhibition in white light in Arabidopsis seedlings.…”

“…The discovery of multiple independent BR-catabolic pathways and their enzymes in Arabidopsis demonstrates the importance of this process in plant growth and development. [1][2][3][4][5][6][7][8][9][10] These BR catabolic pathways were mainly discovered and latter characterized using genetic manipulation of the genes involved. In all cases, in planta overexpression of BR catabolic genes leads to characteristic BR-deficient phenotypes at both seedling and adult stages of Arabidopsis.…”