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Research article2006Peer reviewed

Transcriptional regulation of the sbellb genes in sorghum (Sorghum bicolor) and barley (Hordeum vulgare): Importance of the barley sbellb second intron

Mutisya, J; Sun, CX; Palmqvist, S; Baguma, Y; Odhiambo, B; Jansson, C

Abstract

The transcriptional activity of the sorghum sbellb gene, encoding starch branching enzyme IIb, is seed specific, with expression in both the endosperm and the embryo. In comparison, expression of barley sbellb is confined to the endosperm, whereas that of barley sbella occurs in endosperm, embryonic and vegetative tissues. It has been suggested that the second intron of barley sbellb may be instrumental in conferring endosperm-specific expression. Therefore, to further investigate the regulatory mechanisms of barley and sorghum sbe, we examined the tissue-specific activity of the sorghum sbe promoter in transient assays of green fluorescent protein (gfp) reporter constructs. We found that, when linked to the barley sbellb second intron, the sorghum sbellb promoter could not drive gfp transcription in sorghum or barley embryonic cells. Similar results were obtained for the barley sbella promoter. Database searches showed that sequences homologous to the barley sbellb intron also exist in introns and flanking regions of some other grass genes. Deletion mutagenesis of the sorghum sbellb promoter identified the minimal promoters required for high and low-level expression, respectively, but did not reveal any putative promoter elements crucial for expression. A sequence with similarity to the SURE element, implicated in sugar signaling, was located in the distal promoter region of sorghum sbellb, upstream of the minimal promoters. SURE elements are present in the proximal promoter regions of the sugar-regulated barley iso1 gene, and barley sbellb. In keeping in line with these observations, RNA-gel blot analyses demonstrated that expression of barley sbellb was sugar inducible, whereas that of sorghum sbellb was not. (c) 2005 Elsevier GmbH. All rights reserved

Keywords

barley; intron; sbellb; sorghum

Published in

Journal of Plant Physiology
2006, Volume: 163, number: 7, pages: 770-780
Publisher: ELSEVIER GMBH, URBAN & FISCHER VERLAG