Diurnal regulation of the brassinosteroid-biosynthetic CPD gene in Arabidopsis.
Plant steroid hormones, brassinosteroids (BRs), are essential for normal photomorphogenesis. However, the mechanism by which light controls physiological functions via BRs is not well understood. Using transgenic plants carrying promoter-luciferase reporter gene fusions, we show that in Arabidopsis (Arabidopsis thaliana) the BR-biosynthetic CPD and CYP85A2 genes are under diurnal regulation. The complex diurnal expression profile of CPD is determined by dual, light-dependent, and circadian control. The severely decreased expression level of CPD in phytochrome-deficient background and the red light-specific induction in wild-type plants suggest that light regulation of CPD is primarily mediated by phytochrome signaling. The diurnal rhythmicity of CPD expression is maintained in brassinosteroid insensitive 1 transgenic seedlings, indicating that its transcriptional control is independent of hormonal feedback regulation. Diurnal changes in the expression of CPD and CYP85A2 are accompanied by changes of the endogenous BR content during the day, leading to brassinolide accumulation at the middle of the light phase. We also show that CPD expression is repressed in extended darkness in a BR feedback-dependent manner. In the dark the level of the bioactive hormone did not increase; therefore, our data strongly suggest that light also influences the sensitivity of plants to BRs.
Institute of Plant Biology, Biological Research Center of the Hungarian Academy of Sciences, H-6701 Szeged, Hungary.
Simona
S
Bancos
Anna-Mária
AM
Szatmári
Julie
J
Castle
László
L
Kozma-Bognár
Kyomi
K
Shibata
Takao
T
Yokota
Gerard J
GJ
Bishop
Ferenc
F
Nagy
Miklós
M
Szekeres
D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002940:Circadian Rhythm; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics* / Q000378:metabolism; D025461:Feedback, Physiological; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D008027:Light; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D010834:Phytochrome / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism
D029681:Arabidopsis Proteins; D011993:Recombinant Fusion Proteins; D010834:Phytochrome; D003577:Cytochrome P-450 Enzyme System; C474079:brassinosteroid-6 oxidase 2, Arabidopsis; D008156:Luciferases; C113844:CPD protein, Arabidopsis; D013250:Steroid Hydroxylases