The rice bZIP transcriptional activator RITA-1 is highly expressed during seed development.

Abstract

Systematic protein-DNA binding studies have shown that plant basic leucine zipper (bZIP) proteins exhibit a differential binding specificity for ACGT motifs. Here, we show that the rice transcription activator-1 (RITA-1) displays a broad binding specificity for palindromic ACGT elements, beíng able to bind A-, C-, and G-box but not T-box elements. By using gel mobility shift assays with probes differing in sequences flanking the hexameric core, we identified high-affinity A-, C-, and G-box binding sites. Quantitative and competition DNA binding studies confirmed RITA-1 specificity for these sites. Using rice protoplasts as a transient expression system, we demonstrated that RITA-1 can transactivate reporter genes possessíng high-affinity but not low-affinity RITA-1 binding sites. Our results established a direct relationship between in vivo transactivation and in vitro binding actívity. Transient expression assays that demonstrated the ability of RITA-1 to transactivate a construct containing rita-7 Sflanking sequences suggest that the factor may be autoregulated. Histochemical analysis of transgenic rice plants showed that a rifa-7-P-glucuronidase transgene is expressed in aleurone and endosperm cells of developing rice seeds. We propose that RITA-1 plays a role in the regulation of rice genes expressed in developing rice seeds.

DNA-Binding Study Identifies C-Box and Hybrid C/G-Box or C/A-Box Motifs as High-Affinity Binding Sites for STF1 and LONG HYPOCOTYL5 Proteins

“…which is a C-box binding protein (Cheong et al, 1994), the binding of STF1 to the G-box, coupled with its ability to form heterodimers with GBFs, makes it a novel member of the bZIP protein family because of its capability to recognize both C-box and G-box motifs. Many researchers have also reported the importance of the flanking sequences for DNA-binding of bZIP proteins (Schindler et al, 1992b;Williams et al, 1992;Izawa et al, 1993Izawa et al, , 1994Niu and Guiltinan, 1994;Hong et al, 1995;Martinez-Garcia et al, 1998). However, this study stresses the importance of a single base at position 24 for STF1 binding, which is in contrast to other bZIP proteins that interact with these C-box sequences in an overlapping manner (Fig.…”

The GCN4 motif in a rice glutelin gene is essential for endosperm‐specific gene expression and is activated by Opaque‐2 in transgenic rice plants

“…In transiently transfected rice protoplasts, SPA activates transcription from the rice GCN4 motif to a level similar to that obtained from O2 (Takaiwa et al, unpublished data). The rice bZIP transcriptional activator RITA-1 is highly expressed in aleurone cells of rice endosperm, being able to bind A-, C-and G-boxes (Izawa et al, 1994). Another rice bZIP-type protein, REB, similar to the O2 heterodimerizing partner OHP and sharing limited but significant homology to SPA, binds to a rice α-globulin promoter through a G-box (Nakase et al, 1997).…”

The wheat transcriptional activator SPA: a seed-specific bZIP protein that recognizes the GCN4-like motif in the bifactorial endosperm box of prolamin genes.

“…A potential functional relationship between 02 and SPA may be reflected by the level of sequence conservation within the DNA binding domain of SPA and 02. However, this degree of sequence similarity is also shared by the parsley CPRF-2 protein (Weisshaar et al, 1991), the rice seed protein Osbzippa, and the rice transcriptional activator RITA-1 (Izawa et al, 1994). Little information is available about the tissue specificity and transcription targets of Osbzippa.…”