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S45A, a double recessive mutant at both BnMs1 and BnMs2 loci in Brassica napus, produces no pollen in mature anthers and no seeds by self fertilization.The BnMs1 and BnMs2 genes, which have redundant functions in the control of male fertility, were positioned on the different linkage groups N7 and N16, respectively, and are located at the same locus on Arabidopsis chromosome 1 based on collinearity between Arabidopsis and Brassica.Complementation tests indicated one candidate gene, a member of the cytochrome P450 family, BnCYP704B1 that functioned to restore the male sterility.Scanning electron (SEM) and transmission electron microscopy (TEM) of the developing anther showed that the mutant was severely compromised in pollen wall formation because it apparently lacked sporopollenin or exine.The phenotype was first evident at the tetrad stage (stage 7) of anther development coinciding with maximum BnCYP704B1 mRNA accumulation observed in tapetal cells at stage 7 to 8 (haploid stage).TEM also suggested that the development of the tapetum was seriously defective due to the disturbed lipid metabolism in the S45A mutant.TUNEL (for terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling) assay indicated that the programmed cell death (PCD) pattern of the S45A mutant tapetum was defect.Lipid analysis revealed that the total fatty acids reduced in the S45A mutant, which showed that BnCYP704B1 was involved in lipid metabolism.These data suggest that BnCYP704B1 is participation in a vital tapetum -specific metabolic pathway not only involved in exine formation, but also required for basic tapetal cell development and function.