Dataset Information

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-O-glucosylation 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.

SUBMITTER: Poppenberger B

PROVIDER: S-EPMC1257699 | biostudies-literature | 2005 Oct

REPOSITORIES: biostudies-literature

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The UGT73C5 of Arabidopsis thaliana glucosylates brassinosteroids.

Poppenberger Brigitte B Fujioka Shozo S Soeno Kazuo K George Gilu L GL Vaistij Fabián E FE Hiranuma Sayoko S Seto Hideharu H Takatsuto Suguru S Adam Gerhard G Yoshida Shigeo S Bowles Dianna D

Proceedings of the National Academy of Sciences of the United States of America 20051007 42

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-O-glucosylation of the BRs brassinolide (BL) and casta ...[more]

PMID: 16214889

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Project description:Brassinosteroids (BRs) are growth-promoting steroid hormones that regulate diverse physiological processes in plants. Most BR biosynthetic enzymes belong to the cytochrome P450 (CYP) family. The gene encoding the ultimate step of BR biosynthesis in Arabidopsis likely evolved by gene duplication followed by functional specialization in a dicotyledonous plant-specific manner. To gain insight into the evolution of BRs, we performed a genomic reconstitution of Arabidopsis BR biosynthetic genes in an ancestral vascular plant, the lycophyte Selaginella moellendorffii. Selaginella contains four members of the CYP90 family that cluster together in the CYP85 clan. Similar to known BR biosynthetic genes, the Selaginella CYP90s exhibit eight or ten exons and Selaginella produces a putative BR biosynthetic intermediate. Therefore, we hypothesized that Selaginella CYP90 genes encode BR biosynthetic enzymes. In contrast to typical CYPs in Arabidopsis, Selaginella CYP90E2 and CYP90F1 do not possess amino-terminal signal peptides, suggesting that they do not localize to the endoplasmic reticulum. In addition, one of the three putative CYP reductases (CPRs) that is required for CYP enzyme function co-localized with CYP90E2 and CYP90F1. Treatments with a BR biosynthetic inhibitor, propiconazole, and epi-brassinolide resulted in greatly retarded and increased growth, respectively. This suggests that BRs promote growth in Selaginella, as they do in Arabidopsis. However, BR signaling occurs through different pathways than in Arabidopsis. A sequence homologous to the Arabidopsis BR receptor BRI1 was absent in Selaginella, but downstream components, including BIN2, BSU1, and BZR1, were present. Thus, the mechanism that initiates BR signaling in Selaginella seems to differ from that in Arabidopsis. Our findings suggest that the basic physiological roles of BRs as growth-promoting hormones are conserved in both lycophytes and Arabidopsis; however, different BR molecules and BRI1-based membrane receptor complexes evolved in these plants.

Dataset Information

The UGT73C5 of Arabidopsis thaliana glucosylates brassinosteroids.

Publications

The UGT73C5 of Arabidopsis thaliana glucosylates brassinosteroids.

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