BEN1, a gene encoding a dihydroflavonol 4‐reductase (DFR)‐like protein, regulates the levels of brassinosteroids in Arabidopsis thaliana

Abstract

SummaryThe ben1-1D (bri1-5 enhanced 1-1dominant) mutant was identified via an activation-tagging screen for bri1-5 extragenic modifiers. bri1-5 is a weak mutant allele of the brassinosteroid receptor gene, BRI1. Overexpression of BEN1 greatly enhances the defective phenotypes of bri1-5 plants. Removal of BEN1 by gene disruption in a Col-0 wild-type background, on the other hand, promotes the elongation of organs. Because BEN1 encodes a novel protein homologous to dihydroflavonol 4-reductase (DFR) and anthocyanidin reductase (BAN), BEN1 is probably involved in a brassinosteroid metabolic pathway. Analyses of brassinosteroid profiles demonstrated that BEN1 is indeed responsible for regulating the levels of several brassinosteroids, including typhasterol, castasterone and brassinolide. In vivo feeding and in vitro biochemical assays suggest that BEN1 is probably involved in a new mechanism to regulate brassinosteroid levels. These results provide additional insight into the regulatory mechanisms of bioactive brassinosteroids.

The Arabidopsis geneATST4ais not a typical brassinosteroids catabolic gene

“…This observation is significant since all the known BR catabolic genes characterized so far result in dramatic BR-deficient phenotypes both at seedling and at adult stages when overexpressed in Arabidopsis. [1][2][3][4][5][6][7][8][9][10] This suggests that ATST4a overexpression did not reduce BR content in the transgenic lines. In addition, quantitative transcript analysis of the feedback regulated genes DWF4 and BAS1 also suggests that BR content is not reduced in the ATST4a-OX lines when compared with wild type (Fig.…”

“…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.…”

“…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.…”

“…[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.…”

Cis-Regulatory Elements Determine Germline Specificity and Expression Level of an Isopentenyltransferase Gene in Sperm Cells of Arabidopsis

“…Following sequence verification, these truncated promoter fragments were in vitro recombined into pBIB-BASTA-GFP-GWR and pBIB-BASTA-GUS-GWR (Yuan et al, 2007) to create final binary transformation constructs. IPTPromPB2 was used as a reverse primer for all ten 59-deletions.…”