­­­Response of Citrus CuCRTISO-Like Promoter to Hormones and Abiotic Stresses in Transgenic Arabidopsis

Previously we isolated a carotenoid isomerase gene, CuCRTISO, from Citrus unshiu and also determined the promoter region of CuCRTISO. The CuCRTISO promoter was regulated in a organ- and developmental-specific manner, and responded to hormones and abiotic stresses. Here, we identified an additional gene, CuCRTISO-like, showed homology with CRTISO gene identified from other plants, and also determined the promoter sequence. The CuCRTISO-like promoter and four truncated versions were analyzed by histochemical GUS staining and GUS expression using transgenic Arabidopsis plant harboring CuCRTISO-like promoter-glucuronidase synthase (GUS) reporter gene constructs. The CuCRTISO-like promoter contained several cis-acting elements involved in hormonal and environmental stress. Salicylic acid only induced GUS activity in the pCRTL-prom1 line. Ethylene and drought stress only induced the GUS activity in the pCRTL-Prom4 line, even though from pCRTL-Prom1 to pCRTL-Prom3 lines also contained the same cis-element involved in ethylene and drought stress. Heat stress induced the GUS activity more strongly as the promoter length shortened, except for no GUS activity of pCRTL-Prom5 line. In addition wounding treatment induced GUS activity in the pCRTL-Prom3 line, although pCRTL-Prom1 and pCRTL-Prom2 lines also have a wounding responsive element. The unexpected results of GUS activity suggest that unknown repressive element(s) might exist on the CuCRTISO-like promoter. Taken together, our results suggest that CuCRTISO-like promoter activity is regulated in a developmental and organ-specific manner, and responds to hormones and abiotic stresses.