J. Plant Physiol. 160. 921 – 930 (2003)  Urban & Fischer Verlag http://www.urbanfischer.de/journals/jpp Starch branching enzymes in sorghum (Sorghum bicolor ) and barley (Hordeum vulgare ): Comparative analyses of enzyme structure and gene expression Joel Mutisya 1, 2 , P. Sathish 3 , Chuanxin Sun 1 , Lena Andersson 4 , Staffan Ahlandsberg 1 , Yona Baguma 1, 5 , Sara Palmqvist 1 , Benjamin Odhiambo 2 , Per Åman 4 , Christer Jansson 1 * 1 Department of Plant Biology,The Swedish University ofAgricultural Sciences, P.O. Box 7080, SE-75007 Uppsala, Sweden 2 Kenya Agricultural Research Institute (KARI), P.O. Box 57811, Nairobi, Kenya 3 Genesis Research and Development Corporation Ltd, P.O. Box 50,Auckland, New Zealand 4 Department of Food Science,The Swedish University of Agricultural Sciences, P.O. Box 7051, S-75007, Uppsala, Sweden 5 Department of Crop Science, Makerere University, P.O. Box 7062, Kampala, Uganda Received October 21, 2002 · Accepted February 7, 2003 Summary A genomic clone for starch branching enzyme (SBE) IIb was isolated from a sorghum bacterial artifi- cial chromosome (BAC) library. The promoter and 5′ flanking sequence, the first four exons and int- rons as well as the last exon and the 3′ untranslated region were sequenced. The tentative transcrip- tion start site of sorghum sbeIIb was mapped based on alignment with the maize sbeIIb gene. The exon-intron structure of the 5′ portion of sorghum sbeIIb was similar to that of maize sbeIIb but dif- fered from that of barley sbeIIb. Specifically, the intronic Bbl element involved in the endosperm spe- cific expression of barley sbeIIb was lacking in the sorghum gene. A cDNA clone for sorghum sbeIIb was reverse PCR amplified and found to encode an 803 amino acids long protein. The amino acid sequence of sorghum SBEIIb was compared to that of sorghum SBEI and corresponding enzymes in barley. The overall identity in amino acid sequence was 54% in the central portion of the enzymes. A major difference between the SBEII and SBEI isoforms was a 67 amino acids-long C-terminal exten- sion in the SBEIs. The spatial and temporal expression patterns of sorghum sbeIIb was determined and compared with those of the sorghum gene for SBEI and the barley genes for SBEIIB and SBEI. All four genes exhibited a seed specific expression. However, while barley sbeIIb and sbeI tran- scripts were detected exclusively in the endosperm, the sorghum genes were expressed also in the embryo. The activity of sorghum sbeIIb and sbeI exhibited a late onset, with a peak of transcription at around 22 days after pollination. This is similar to the pattern of barley sbeI but different from that of barley sbeIIb, which showed a peak of transcription at 12 days after pollination. Key words: sorghum – starch branching enzyme Abbreviations: d.a.p. = days after pollination * E-mail corresponding author: christer.jansson@vbsg.slu.se The genomic and cDNA sequences of sorghum sbeIIb and the cDNA sequence of barley sbeI will appear in GenBank under the accession nos. AY304539, AY304540, and AY304541, respectively. 0176-1617/03/160/08-921 $ 15.00/0