Os02g0709400

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Annotated Information

Function

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   The rice (Oryza sativa L.) basic leucine Zipper factor RISBZ1 and rice prolamin box binding factor (RPBF) are transcriptional activators of rice seed storage protein (SSP) genes in vivo. Storage lipids were accumulated at reduced levels in KD-RISBZ1 and KD-RISBZ1/KD-RPBF seeds. KD-RPBF and KD-RISBZ1/KD-RPBF seeds exhibited multi-layered aleurone cells. Gene expression of DEFECTIVE KERNEL1 (OsDEK1), CRINKLY4 (OsCR4) and SUPERNUMERARY ALEURONE LAYER 1 (OsSAL1) rice homologues was decreased in the KD mutants, suggesting that these genes are regulated by RISBZ1 and RPBF. These phenotypes suggest that combinatorial interactions between RISBZ1 and RPBF play an essential role during grain filling. The functional redundancy and compensation between RISBZ1 and RPBF possibly account for weak effects on the SSP levels in single KD mutants, and help maintain various processes during seed development in rice. Physical interaction between RISBZ1 and RPBF may ensure that these processes are carried out properly.
   DEK1 and is a calpain-like proteinase and a receptor-like kinase,(Becraft et al., 1996; Lid et al., 2002). Both DEK1 binds to the plasma membrane, and is involved in the production of the aleurone layer specification signal. The multiple aleurone layer phenotype in sal1 is thought to be caused by an overabundance of aleurone membrane signaling proteins, such as DEK1 and CR4 (Tian et al., 2007).Previous studies on maize and Arabidopsis,CRINKLY 4 (CR4), DEFECTIVE KERNEL 1 (DEK1) and SUPERNUMERARY ALEURONE LAYER 1 (SAL1) have shown them to be key players in determining the number of aleurone layers (Becraft et al., 1996; Lid et al., 2002; Shen et al., 2003).The expression of both positive (OsCR4 and OsDEK1) and negative (OsSAL1) determining genes for the aleurone layer number was decreased in KD-RISBZ1 and KD-RPBF, and significantly decreased in KD-RISBZ1/KD-RPBF seeds, suggesting that both RISBZ1 and RPBF are positive regulators of these genes.
   Plant seed storage proteins (SSPs) are specifically synthesized during seed maturation, then stored in the seed as a nitrogen source for the germinating seedling, and thus serve as nutrients for humans and livestock. Aside from their physiological and agricultural importance, SSP genes provide an important model system for investigating the temporal and spatial patterns of gene regulation in plants (Goldberg et al., 1994; Kroj et al., 2003). A hallmark of SSP

expression is that it is restricted to maturing seeds (i.e. cotyledons and embryos in dicots, or the endosperm in cereals). Additionally, as SSP genes are expressed at extremely high levels during specific stages in seed development, much of what is known about seed-specific expression can be applied to the production of high-value recombinantproteins in the seeds of transgenic crops (Stoger et al., 2005; Takaiwa et al., 2007). Most cereals, such as maize (Zea mays L.), barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.),produce prolamins as their major SSP (Shewry and Tatham, 1999), but rice (Oryza sativa L.) accumulates glutelins, which are homologous with the 11S globulins of legumes (Takaiwa et al., 1999), as the major component. Irrespective of the evolutionary divergence between the prolamin and glutelin genes, cereal SSP genes are expressed in the endosperm. Several motifs, including GCN4, a prolamin box (P box), AACA and ACGT, have been identified as cis-regulatory elements involved in the endosperm-specific expression of cereal SSP genes (Zheng et al., 1993; Takaiwa et al., 1996; Washida et al., 1999; Wu et al., 2000).

Expression

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   DEK1 and CR4 are a calpain-like proteinase and a receptor-like kinase, respectively (Becraft et al., 1996; Lid et al., 2002). Both DEK1 and CR4 bind to the plasma membrane, and are involved in the production of the aleurone layer specification signal. The multiple aleurone layer phenotype in sal1 is thought to be

caused by an overabundance of aleurone membrane signaling proteins, such as DEK1 and CR4 (Tian et al., 2007).

Evolution

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Labs working on this gene

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References

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