SURE (sugar responsive) is a cis element in plant sugar signaling. The SURE element was reported first for potato, in which it confers sugar responsiveness to the patatin promoter. A SURE binding transcription factor has not been isolated. We have isolated a transcription factor cDNA from barley and purified the corresponding protein. The transcription factor, SUSIBA2 (sugar signaling in barley), belongs to the WRKY proteins and was shown to bind to SURE and W-box elements but not to the SP8a element in the iso1 promoter. Nuclear localization of SUSIBA2 was demonstrated in a transient assay system with a SUSIBA2:green fluorescent protein fusion protein. Exploiting the novel transcription factor oligodeoxynucleotide decoy strategy with transformed barley endosperm provided experimental evidence for the importance of the SURE elements in iso1 transcription. Antibodies against SUSIBA2 were produced, and the expression pattern for susiba2 was determined at the RNA and protein levels. It was found that susiba2 is expressed in endosperm but not in leaves. Transcription of susiba2 is sugar inducible, and ectopic susiba2 expression was obtained in sugar-treated leaves. Likewise, binding to SURE elements was observed for nuclear extracts from sugar-treated but not from control barley leaves. The temporal expression of susiba2 in barley endosperm followed that of iso1 and endogenous sucrose levels, with a peak at ف 12 days after pollination. Our data indicate that SUSIBA2 binds to the SURE elements in the barley iso1 promoter as an activator. Furthermore, they show that SUSIBA2 is a regulatory transcription factor in starch synthesis and demonstrate the involvement of a WRKY protein in carbohydrate anabolism. Orthologs to SUSIBA2 were isolated from rice and wheat endosperm.
Pig small intestine was used as starting material for a batchwise isolation of a peptide fraction enriched in antibacterial activities against Escherichia coli (anti-Ec factor) and against Bacillus megaterium (anti-Bm factor). Separation and further purification were by different types of chromatography. Sequence analysis showed the anti-Bm factor to be apparently similar to vasoactive intestinal peptide. The anti-Ec factor was found to have a 31-residue sequence that was cecropin-like. It was named cecropin P1 and its structure was confirmed by solid-phase synthesis. Synthetic cecropin P1 with and without C-terminal amide was assayed on eight different bacteria. Mobility comparison between synthetic and natural cecropin P1 indicates that the natural peptide has a free C-terminal carboxyl group.
The sbeIIa and sbeIIb genes, encoding starch-branching enzyme (SBE) IIa and SBEIIb in barley (Hordeum vulgare L.), have been isolated. The 5 portions of the two genes are strongly divergent, primarily due to the 2064-nucleotide-long intron 2 in sbeIIb. The sequence of this intron shows that it contains a retro-transposonlike element. Expression of sbeIIb but not sbeIIa was found to be endosperm specific. The temporal expression patterns for sbeIIa and sbeIIb were similar and peaked around 12 d after pollination. DNA gel-blot analysis demonstrated that sbeIIa and sbeIIb are both single-copy genes in the barley genome. By fluorescence in situ hybridization, the sbeIIa and sbeIIb genes were mapped to chromosomes 2 and 5, respectively. The cDNA clones for SBEIIa and SBEIIb were isolated and sequenced. The amino acid sequences of SBEIIa and SBEIIb were almost 80% identical. The major structural difference between the two enzymes was the presence of a 94-amino acid N-terminal extension in the SBEIIb precursor. The (/ ␣) 8 -barrel topology of the ␣-amylase superfamily and the catalytic residues implicated in branching enzymes are conserved in both barley enzymes.Starch is a mixture of amylose and amylopectin, both of which are Glc polymers. Amylose is a mostly linear polymer of 200 to 2000 ␣-1,4-bonded Glc moieties with rare ␣-1,6 branch points (for reviews, see Martin and Smith, 1995; Ball et al., 1996). Amylopectin is highly ␣-1,6-branched, with a complex structure of 10 6 to 10 8 M r and up to 3 ϫ 10 6 Glc subunits, making it one of the largest biological molecules in nature. In the plant, starch is deposited as starch granules in chloroplasts of photosynthetic tissues or in amyloplasts of endosperm, embryos, tubers, and roots. In most plants, starch consists of 20% to 30% amylose and 70% to 80% amylopectin. In photosynthetic and nonphotosynthetic tissues the Glc moiety of ADP-Glc is incorporated in the growing amylose polymer with the help of starch synthases. The formation of ␣-1,6 linkages in amylopectin is catalyzed by SBEs (EC 2.4.1.18). The final structure of amylopectin is governed by the activities of different SBEs, starch synthases, and a debranching enzyme (Ball et al., 1996).SBEs exist as several isoforms in developing storage tissues of maize, rice, pea (for review, see Martin and Smith, 1995), barley (Sun et al., 1996(Sun et al., , 1997, wheat (Morell et al., 1997), potato (Larsson et al., 1996), and Arabidopsis (Fisher et al., 1996). SBEs can be separated into two major groups based on structural and catalytic properties. One group, referred to as SBE family II or A (Martin and Smith, 1995), comprises SBEII from maize (Fisher et al., 1993; Gao et al., 1997), wheat (Nair et al., 1997), and potato (Larsson et al., 1996), SBE3 from rice (Mizuno et al., 1993), SBEI from pea (Bhattacharyya et al., 1990), and SBE2 from Arabidopsis (Fisher et al., 1996). The other group, SBE family I or B (Martin and Smith, 1995), comprises SBEI from maize (Baba at al., 1991), wheat (Morell et al., 1997), potato (Kossm...
SummarySugar signalling cascades are important components of regulatory networks in cells. Compared with the situation in bacteria, yeast and animals, participants of the sugar signalling pathways in plants are poorly understood. Several genes involved in starch synthesis are known to be sugar inducible, although the signal transduction pathways remain undisclosed. We reported recently the isolation of SUSIBA2, a transcription factor involved in sugar-mediated regulation of starch synthesis. Here, we used antisense oligodeoxynucleotide (ODN) inhibition, a powerful approach in medical sciences, to block the effects of SUSIBA2 in sugartreated barley leaves. The uptake and intracellular trafficking of an 18-mer susiba2 antisense ODN in leaves were followed by confocal microscopy. Administration of the antisense ODN to the leaves impeded susiba2 expression by RNase H activation. This dramatically diminished the ectopic expression of the iso1 and sbeIIb genes and resulted in altered starch synthesis. This study illustrates the successful exploitation of the antisense ODN technology in plant biology, e.g. as a rapid antecedent to time-consuming transgenic studies, and identifies SUSIBA2 as a transcriptional activator in plant sugar signalling. Based on our findings, we propose a model for sugar-signalling control of starch synthesis.
Atmospheric methane is the second most important greenhouse gas after carbon dioxide, and is responsible for about 20% of the global warming effect since pre-industrial times. Rice paddies are the largest anthropogenic methane source and produce 7-17% of atmospheric methane. Warm waterlogged soil and exuded nutrients from rice roots provide ideal conditions for methanogenesis in paddies with annual methane emissions of 25-100-million tonnes. This scenario will be exacerbated by an expansion in rice cultivation needed to meet the escalating demand for food in the coming decades. There is an urgent need to establish sustainable technologies for increasing rice production while reducing methane fluxes from rice paddies. However, ongoing efforts for methane mitigation in rice paddies are mainly based on farming practices and measures that are difficult to implement. Despite proposed strategies to increase rice productivity and reduce methane emissions, no high-starch low-methane-emission rice has been developed. Here we show that the addition of a single transcription factor gene, barley SUSIBA2 (refs 7, 8), conferred a shift of carbon flux to SUSIBA2 rice, favouring the allocation of photosynthates to aboveground biomass over allocation to roots. The altered allocation resulted in an increased biomass and starch content in the seeds and stems, and suppressed methanogenesis, possibly through a reduction in root exudates. Three-year field trials in China demonstrated that the cultivation of SUSIBA2 rice was associated with a significant reduction in methane emissions and a decrease in rhizospheric methanogen levels. SUSIBA2 rice offers a sustainable means of providing increased starch content for food production while reducing greenhouse gas emissions from rice cultivation. Approaches to increase rice productivity and reduce methane emissions as seen in SUSIBA2 rice may be particularly beneficial in a future climate with rising temperatures resulting in increased methane emissions from paddies.
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