A single copy gene has been isolated, termed GOS2, from rice. Sequence comparison revealed highly similar genes in mammals and yeast, indicating that GOS2 encodes an evolutionary conserved protein. GOS2 mRNA was detected in all tissues examined. When the upstream region was translationally fused to the reporter gene gusA it was found to drive expression in a variety of rice tissues and in cell suspensions of other monocot species following introduction by particle bombardment. Therefore, the GOS2promoter is potentially useful for genetic engineering of monoocots, A DNA-binding activity from rice, termed rice ASF-1, with similar binding specificity as the cloned tobacco transcription factor TGA-1a, was found to bind to a TGACG sequence motif in the GOS2promoter. Possible roles for rice ASF-1 in the transcriptional activation of the GOS2 promoter are discussed.
Many plant genes examined to date are regulated by various endogenous or environmental factors. Extensively studied examples are light-regulated and leaf-specific genes (Cuozzo et al., 1988) and seed-specific genes (Goldberg et al., 1989). In contrast, relatively little is known about plant genes that are ubiquitously expressed. Promoters that are active in many different plant tissues and that have been analysed in some detail are either from viral or bacterial origin: the 35S promoter from cauliflower mosaic virus (CaMV) (Benfey et al., 1989) and promoters of the octopine synthase (ocs) (Kononowicz et al., 1992)
Received 5 December 1991; revised 9 April 1992.
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and nopaline synthase (nos) (An et al., 1988) genes from the Agrobacterium tumefaciens T -DNA.
Sequence elements important for high-level expression of these promoters (Ellis et al., 198?; Fang et al., 1989; Mitra and An, 1989) contain the core motifTGACG. Transsacting factors binding to this motif have been characterized (Fromm etal., 1989; Lam etal., 1989, 1990; Lohmer etal., 1991; Prat et al., 1989; Singh et al., 1989; Tokuhisa et al., 1990) and cloned (Hartings et al., 1989; Katagiri et al., 1989; Singh et al., 1990; Tabata et al., 1989, 1991). Sequence analysis of the cDNA clones showed that the proteins belong to the leucine zipper (bZIP) class of trannscription factors (McKnight, 1991). The tobacco bZIP protein TGA-1 a was shown to function as a transcriptional activator in human and plant in vitro transcription systems (Katagiri et al., 1990; Yamazaki et al., 1990).
The CaMV 35S promoter and the nos promoter are widely used to monitor plant transformation procedures and to express useful traits. Since the number of promoters known to be active in many different plant tissues is very limited, isolation of other promoters, in particular ones that are active in monocots, is desirable. Knowledge about cissacting elements and trans-acting factors essential for the activity of such promoters increases their potential for sophisticated applications and in addition enhances our understanding of transcription processes in plants.
Here we describe the isolation of the rice gene GOS2, which is expressed in all tissues examined and we present an initial analysis of its promoter region.