title: A cytochrome P450 monooxygenase commonly used for negative selection in transgenic plants causes growth anomalies by disrupting brassinosteroid signaling.
abstract: BACKGROUND
  Cytochrome P450 monooxygenases form a large superfamily of enzymes that catalyze diverse reactions. The P450 SU1 gene from the soil bacteria Streptomyces griseolus encodes CYP105A1 which acts on various substrates including sulfonylurea herbicides, vitamin D, coumarins, and based on the work presented here, brassinosteroids. P450 SU1 is used as a negative-selection marker in plants because CYP105A1 converts the relatively benign sulfonyl urea pro-herbicide R7402 into a highly phytotoxic product. Consistent with its use for negative selection, transgenic Arabidopsis plants were generated with P450 SU1 situated between recognition sequences for FLP recombinase from yeast to select for recombinase-mediated excision. However, unexpected and prominent developmental aberrations resembling those described for mutants defective in brassinosteroid signaling were observed in many of the lines.
  
  
  RESULTS
  The phenotypes of the most affected lines included severe stunting, leaf curling, darkened leaves characteristic of anthocyanin accumulation, delayed transition to flowering, low pollen and seed yields, and delayed senescence. Phenotype severity correlated with P450 SU1 transcript abundance, but not with transcript abundance of other experimental genes, strongly implicating CYP105A1 as responsible for the defects. Germination and seedling growth of transgenic and control lines in the presence and absence of 24-epibrassinolide indicated that CYP105A1 disrupts brassinosteroid signaling, most likely by inactivating brassinosteroids.
  
  
  CONCLUSIONS
  Despite prior use of this gene as a genetic tool, deleterious growth in the absence of R7402 has not been elaborated. We show that this gene can cause aberrant growth by disrupting brassinosteroid signaling and affecting homeostasis.
authors.affiliation: University of North Texas, Department of Biological Sciences, 1155 Union Circle #305220, Denton, TX 76203-5017, USA.
authors.forename: Kasturi
authors.initials: K
authors.lastname: Dasgupta
authors.forename: Savita
authors.initials: S
authors.lastname: Ganesan
authors.forename: Sindhu
authors.initials: S
authors.lastname: Manivasagam
authors.forename: Brian G
authors.initials: BG
authors.lastname: Ayre
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D005818:Genetic Engineering; D010937:Plant Growth Regulators / Q000096:biosynthesis*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D015398:Signal Transduction; D013302:Streptomyces / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D010937:Plant Growth Regulators; D003577:Cytochrome P-450 Enzyme System