The promoter from the Citrus unshiu carotenoid isomerase gene directs differential GUS expression in transgenic Arabidopsis

Carotenoid isomerase (CRTISO) catalyzes the isomerization of prolycopene to all-trans-lycopene in the carotenoid biosynthetic pathway. We isolated a promoter region of CuCRTISO from Citrus unshiu. We determined whether the promoter encoded organ-specific or developmental-specific expression and identified possible cis-acting promoter elements. The promoter and two truncated versions were fused to the β-glucuronidase (GUS) gene and transformed into Arabidopsis thaliana. Transgenic lines expressing the 2501-bp promoter (pCiso-Prom1) and truncated promoters (pCiso-Prom2 and pCiso-Prom3) showed the same developmental and organ-specific activity. GUS expression was detected in the cotyledon and root at 5 and 10 days after germination, mature leaf, and anther. The CuCRTISO promoter contained several cis-acting elements involved in hormonal and environmental stress. Drought stress or abscisic acid treatment did not induce GUS expression in any transgenic lines. Heat stress induced GUS expression in the pCiso-Prom1 line; this promoter construct contains the heat stress-responsive element. Ethylene and cold stress treatments induced GUS expression only in the pCiso-Prom3 line, although all transgenic lines contained the same cis-acting ethylene and low-temperature response elements, which could indicate the existence of unknown repressor element(s) in the CuCRTISO promoter. The CuCRTISO expression of Citrus unshiu during fruit maturation showed that in the green stage, it was highly expressed and then subsequently decreased after the stage. These studies indicate that CuCRTISO promoter activity is regulated in a developmental and organ-specific manner that responds to heat, cold, and ethylene. These results provide new insights into the role of cis-acting element(s) in CuCRTISO promoter activity.