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Identification and Biosynthesis of C-24 Ethylidene Brassinosteroids in Arabidopsis thaliana
노지희,염현숭,장환희,김선영,윤지현,김성기 한국식물학회 2017 Journal of Plant Biology Vol.60 No.5
Isofucosterol is a major 4-demethylsterol whichhas an ethylidene group at C-24 in Arabidopsis thaliana. Toevaluate the presence of brassinosteroids (BRs) with thesame carbon skeleton as that of isofucosterol, a large quantity ofA. thaliana was extracted and purified. GC-MS/selected ionmonitoring analysis verified that 6-deoxohomodolichosteroneand homodolichosterone are present in Arabidopsis. Anenzyme solution prepared from wild type Arabidopsissuccessfully mediated conversion of 6-deoxohomodolichosteroneto homodolichosterone. However, a double mutant cyp85a1/cyp85a2 could not catalyze the conversion, implying that inA. thaliana the C-6 oxidation of 6-deoxohomodolichosteroneto homodolichosterone seems to be catalyzed by CYP85A1and/or CYP85A2. In yeast, both heterologously expressedCYP85A1 and CYP85A2 catalyzed the C-6 oxidation of 6-deoxohomodolichosterone to homodolichosterone, but theconversion rate in CYP85A2/V60/WAT21 was significantlyhigher than that in CYP85A1/V60/WAT21, indicating thatC-6 oxidation of 6-deoxohomodolichosterone to homodolichosteroneis mainly catalyzed by CYP85A2 in A. thaliana. Taken together, this study strongly suggests that a biosyntheticpathway for the production of 6-deoxohomodolichosteroneand homodolichosterone is functional, and CYP85As haveimportant roles in 24-ethylidene biosynthesis in A. thaliana.
Brassinosteroid signaling modulates submergence-induced hyponastic growth in Arabidopsis thaliana
윤지현,강승혜,노지희,이지은,염현숭,김성기 한국식물학회 2016 Journal of Plant Biology Vol.59 No.4
The role of brassinosteroids (BRs) in hyponastic growth induced by submergence was investigated in Arabidopsis thaliana. Under flooding conditions, exogenously applied BRs increased hyponastic growth of rosette leaves. This hyponastic growth was reduced in a BR insensitive mutant (bri1-5), while it was increased in a BR dominant mutant (bes1-D). Further, expression of hypoxia marker genes, HRE1 and HRE2, was elevated in submerged bes1-D. These results indicate that BRs exert a positive action on hyponastic growth of submerged Arabidopsis leaves. Expression of ethylene biosynthetic genes, such as ACS6, ACS8 and ACO1, which are up-regulated by submergence, was also activated by application of BRs and in bes1-D. The enhanced hyponastic growth in submerged bes1-D was significantly reduced by application of cobalt ion, suggesting that BRs control hyponastic growth via ethylene, which seems to be synthesized by ACO6 and ACO8 followed by ACO1 in submerged leaves. A double mutant, bes1-Dxaco1-1, showed hyponastic growth activity similar to that seen in aco1-1, demonstrating that the BR signaling for regulation of hyponastic growth seems to be an upstream event in ethylene-induced hyponastic growth under submergence in Arabidopsis.