Synergism between RPBF Dof and RISBZ1 bZIP Activators in the Regulation of Rice Seed Expression Genes

Abstract

The Dof (DNA binding with one finger) transcriptional activator rice (Oryza sativa) prolamin box binding factor (RPBF), which is involved in gene regulation of rice seed storage proteins, has been isolated from rice cDNA expressed sequence tag clones containing the conserved Dof. RPBF is found as a single gene per haploid genome. Comparison of RPBF genomic and cDNA sequences revealed that the genomic copy is interrupted by one long intron of 1,892 bp in the 5# noncoding region. We demonstrated by transient expression in rice callus protoplasts that the isolated RPBF trans-activated several storage protein genes via an AAAG target sequence located within their promoters, and with methylation interference experiments the additional AAAG-like sequences in promoters of genes expressed in maturing seeds were recognized by the RPBF protein.Binding was sequence specific, since mutation of the AAAG motif or its derivatives decreased both binding and transactivation by RPBF. Synergism between RPBF and RISBZ1 recognizing the GCN4 motif [TGA(G/C)TCA] was observed in the expression of many storage protein genes. Overexpression of both transcription factors gave rise to much higher levels of expression than the sum of individual activities elicited by either RPBF or RISBZ1 alone. Furthermore, mutation of recognition sites suppressed reciprocal trans-activation ability, indicating that there are mutual interactions between RISBZ1 and RPBF. The RPBF gene is predominantly expressed in maturing endosperm and coordinately expressed with seed storage protein genes, and is involved in the quantitative regulation of genes expressed in the endosperm in cooperation with RISBZ1.

AP2-ERF Transcription Factors Mediate Nod Factor–Dependent MtENOD11Activation in Root Hairs via a Novelcis-Regulatory Motif

“…These flanking or overlapping nucleotides can contribute to the binding affinity of transcription factors to the central GC-rich region, as reported previously for other factors (Tournier et al, 2003;Xue and Loveridge, 2004). Alternatively, the GCC-like motif may act in cooperation with neighboring cis motifs to specify expression, as has been reported for a number of plant genes (Buttner and Singh, 1997;Riechmann and Meyerowitz, 1998;Diaz et al, 2002;Brown et al, 2003;Yamamoto et al, 2006). The future characterization of the core cis-regulatory elements specifically recognized by ERN factors should make it possible to scan the M. truncatula genome to discover NF-dependent regulons.…”

Genome-wide identification and characterization of the Dof gene family in Medicago truncatula

“…In cereal seeds, most Dof genes are expressed during both seed germination and maturation, recognizing the 5'-TGTAAAG-3' motif, and are termed Prolamin-box binding factors (PBF). These Dof genes have a high degree of sequence similarity to other Dof genes, including ZmPBF from maize (Schneidereit et al, 2008), OsPBF from rice (Yamamoto et al, 2006), WPBF from wheat (Mena et al, 1998;Dong et al, 2007), BPBF from barley (Mena et al, 1998), and FMPBF from finger millet . These genes have similar expression profiles with similar functions in the development of the endosperm during the seed-filling phase.…”

Combinatorial Networks Regulating Seed Development and Seed Filling

“…Nonetheless, part of the seed maturation program is regulated by indirect means mediated by STF. In rice, mutual interactions have been demonstrated between two transcriptional activators, a DOF-related rice prolamin box binding protein (RPBF) and a RISBZ1 bZIP factor (Yamamoto et al, 2006). In barley, the formation of binary or ternary complexes with PBF and DOF regulatory proteins are important for controlling SSP gene expression (Rubio-Somoza et al, 2006a;2006b;Yamamoto et al, 2006).…”

“…In rice, mutual interactions have been demonstrated between two transcriptional activators, a DOF-related rice prolamin box binding protein (RPBF) and a RISBZ1 bZIP factor (Yamamoto et al, 2006). In barley, the formation of binary or ternary complexes with PBF and DOF regulatory proteins are important for controlling SSP gene expression (Rubio-Somoza et al, 2006a;2006b;Yamamoto et al, 2006). In Arabidopsis, mutation of LEC-type regulators (LEC1, LEC2 and FUS3) led to reduced accumulation of SSPs and major seed lipid TAGs, while ectopic expression in seedlings caused SSPs and TAGs to accumulate in vegetative tissues (Kagaya et al, 2005b;SantosMendoza et al, 2005;Braybrook et al, 2006;Wang et al, 2007).…”