A cytochrome P450 monooxygenase commonly used for negative selection in transgenic plants causes growth anomalies by disrupting brassinosteroid signaling

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 P450SU1 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.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.Cytochrome P450 monooxygenases (CYPs) form a large superfamily composed of many genes from many organisms. The reactions catalyzed by these enzymes are extremely diverse, but generally involve the transfer of one atom from molecular oxygen to a substrate and reduction of the other atom to form water at the expense of NADPH or NADH [1,2]. CYPs are therefore classified as monooxygenases, but in addition to hydroxylation [3], CYPs can catalyze oxidation [4], dealkylation [5], deamination, dehalogenation and sulfoxide formation [6]. Arabidopsis thaliana has 272 predicted CYP genes (246 predicted full-length genes and 26 pseudogene fragments) making it one of the largest gene families in higher plants. The encoded enzymes participate in the anabolism or catabolism of membrane sterols, structural polymers, hormones and many secondary metabolites functioning as pigments, antioxidants and defense compounds. CYP enzymes can also detoxify exogenous molecules such as pesticides and pollutants [1].CYP enzymes are important regulators of plant growth because they catalyze the synthesis or degradation of several hormones includ