Isolation and characterization of a Citrus FT/TFL1 homologue (CuMFT1), which shows quantitatively preferential expression in Citrus seeds

Abstract

A Citrus FT/TFL1 homologue (CuMFT1) was isolated from Satsuma mandarin (Citrus unshiu Marc.), and a high degree of expression was detected in mature seeds, indicating that its promoter is expected to induce the expression of a target gene in the late embryonic stage of Citrus seed. To obtain a seed-specific promoter useful for Citrus transgenic research, the 5′ upstream region of CuMFT1 was isolated from the BAC library, and its promoter activity was characterized using particle bombardment and transgenic Arabidopsis. The 2.4 kbp in the 5′ upstream region (CuMFT1 promoter) contained RY (CATGCAT), E-box (CANNTG), and distant B-box (GCCACTTGTC) cis-elements, which have been reported to promote seed-specific gene expression in plants. The CuMFT1 promoter fused to the uidA gene was directly incorporated into tissues from Citrus and its relatives using particle bombardment. The results showed that the CuMFT1 promoter conferred high β-glucronidase (GUS) activity in seed. The CuMFT1 promoter-GUS fusion construct was also incorporated into Arabidopsis, and transgenic Arabidopsis was evaluated by histochemical staining and fluorometric GUS analysis. The experiments revealed that the CuMFT1 promoter conferred quantitatively preferential expression in Arabidopsis seeds; thus, it was suggested that the cis-elements in the CuMFT1 promoter required for expression in Citrus seed were functionally conserved in the heterologous Arabidopsis plant. The CuMFT1 promoter could be utilized as a promoter regulating the quantitatively preferential expression in seed, and is useful for studies of seed development and manipulation by genetic engineering in Citrus and Arabidopsis. JSHS © 2008.