Abstract: By using transgenic rice plants of 5′ deletion Pib promoter fragment-gus constructions, the relationships between the copy number of motif YTCANTYY in Pib promoter and activity of Pib promoter and its darkness induction attribute were systematically analyzed. The results from GUS histochemistry analysis revealed, after darkness induction the transgenic rice calli of Pib promoter fragments harboring 6, 3, or 1 copy of YTCANTYY motif were developed GUS blue to a different degree in X-gluc solution, but the 5′ deletion Pib promoter fragment without any YTCANTYY was unable to drive gus gene to show any GUS blue. Fluorescence quantitative analysis results showed that Pib promoter sequence had strong organ specificity. Even for the 222 bp fragment of 5′ deletion Pib promoter, which does not contain YTCANTYY motif, in its transgenic rice plants the Pib promoter activity of root was higher than that of above ground organs. But the activities of promotion and darkness inducing were increased with the increase of promoter fragments in length and the increase of this motif copy. These results indicated that YTCANTYY in Pib promoter is a functional motif for darkness induction and in other words this motif confers the darkness induction on Pib promoter. At least within 6 copies, the activity of darkness induction was positively correlated with the copy number of YTCANTYY. And the activity of darkness induction for each individual YTCANTYY motif seemed to be additive.

Key words: Rice, Pib gene, Promoter, Darkness inducing motif