A carrot G-box binding factor-type basic region/leucine zipper factor DcBZ1 is involved in abscisic acid signal transduction in somatic embryogenesis.

Carrot (Daucus carota) somatic embryogenesis has been extensively used as an experimental system for studying embryogenesis. In maturing zygotic embryos, abscisic acid (ABA) is involved in acquisition of desiccation tolerance and dormancy. On the other hand, somatic embryos contain low levels of endogenous ABA and show desiccation intolerance and lack dormancy, but tolerance and dormancy can be induced by exogenous application of ABA. In ABA-treated carrot embryos, some ABA-inducible genes are expressed. We isolated the Daucus carota bZIP1 (DcBZ1) gene encoding a G-box binding factor-type basic region/leucine zipper (GBF-type bZIP) factor from carrot somatic embryos. The expression of DcBZ1 was detected in embryogenic cells, non-embryogenic cells, somatic embryos, developing seeds, seedlings, and true leaves. Notably, higher expression was detected in embryogenic cells, true leaves, and seedlings. The expression of DcBZ1 increased in seedlings and true leaves after ABA treatment, whereas expression was not affected by differences in light conditions. During the development of zygotic and somatic embryos, increased expression of DcBZ1 was commonly detected in the later phase of development. The recombinant DcBZ1 protein showed specific binding activity to the two ABA-responsive element-like motifs (motif X and motif Y) in the promoter region of the carrot ABA-inducible gene according to results from an electrophoretic mobility shift assay. Our findings suggest that the carrot GBF-type bZIP factor, DcBZ1, is involved in ABA signal transduction in embryogenesis and other vegetative tissues.

NtWBC1, an ABC transporter gene specifically expressed in tobacco reproductive organs.

To identify genes specifically or predominantly expressed in the stigmas/styles and to establish their possible function in the reproductive process of plants, a tobacco stigma/style cDNA library was constructed and differentially screened, resulting in the isolation of several cDNA clones. The molecular characterization of one of these clones is described here. After sequencing the cDNA and the isolated genomic clone, it was determined that the corresponding gene encodes a protein containing an ATP-binding cassette, characteristic of ABC transporters. This gene, designated as NtWBC1 (Nicotiana tabacum ABC transporter of the White-Brown Complex subfamily), encodes a protein that contains the typical structure of the 'half-transporters' of the White subfamily. To establish the spatial expression pattern of the NtWBC1 gene, northern blot and real-time RT-PCR analyses with total RNA from roots, stems, leaves, sepals, petals, stamens, stigmas/styles, ovaries, and seeds were performed. The result revealed a transcript of 2.5 kb present at high levels in stigmas and styles and a smaller transcript (2.3 kb) present at a lower level in stamens. NtWBC1 expression is developmentally regulated in stigmas/styles, with mRNA accumulation increasing toward anthesis. In situ hybridization experiments demonstrated that NtWBC1 is expressed in the stigmatic secretory zone and in anthers, at the stomium region and at the vascular bundle. NtWBC1 is the first ABC transporter gene with specific expression in plant reproductive organs to be identified and its expression pattern suggests important role(s) in the reproductive process.