To investigate whether the reduction of the gene’s transcription level from mutated sscd1–1 in Arabidopsis is induced by splicing efficiency or its own promoter regulation, expression vectors of exogenous 35S promoter and endogenous promoter driven by normal SSCD1 gene and sscd1–1 mutated gene respectively were firstly constructed, then it was transformed into Arabidopsis sscd1–1 mutant, the expression of the sscd1–1 mutated gene was analyzed by RT–PCR. The results showed that its expression did not affected by 35S promoter driven by sscd1–1 mutated gene, however, the expression level of sscd1–1 mutated gene driven by its endogenous promoter was significantly decreased. Hence, the point mutation in sscd1–1 did not affect the splicing efficiency of the sscd1–1 gene, the reduction of sscd1–1 expression level was caused by its endogenous promoter.