POLYMORPHISM IN THE PROMOTER REGION OF THE SUCROSE SYNTHASE-2 GENE OF SACCHARUM GENOTYPES

Authors: Lingle, Sarah; Dyer, John

Submitted to: American Society of Sugar Cane Technologists
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2004
Publication Date: 11/22/2004
Citation: Lingle, S.E., Dyer, J.M. 2004. Polymorphism in the promoter region of the sucrose synthase-2 gene of Saccharum genotypes. Journal of the American Society of Sugar Cane Technologists. 24:241-249.

Interpretive Summary: Sucrose synthase is a protein that may contribute to sucrose accumulation in sugarcane. We isolated the gene that codes for sucrose synthase in sugarcane, and determined its sequence. This is the first gene entirely sequenced in sugarcane. The promoter of the gene is the first part of the sequence that determines how much, when and where the gene is turned on. We compared the sequences of the promoter in different species that are crossed to make commercial sugarcane varieties. There were significant differences in the sequence within each species, because it has more than the usual two copies of each chromosome, and also between species. These differences may explain differences between species in how much the gene is expressed, or turned on, in different parts of the plant. They will also be useful as markers for the sucrose gene, so that sugarcane breeders can select seedlings with greater likelihoods of having high sucrose concentrations.

Technical Abstract: Sucrose synthase (E.C. 2.4.1.13) is an important enzyme of sucrose metabolism in sugarcane (Saccharum spp. hybrids). We isolated and sequenced the entire gene encoding one of the forms of sucrose synthase, Sus2, in sugarcane. This gene is homologous to Sh1 in maize (Zea mays L.). The entire sequence is 7771 base pairs long (GenBank accession AY118266), and contains 16 exons. It shares many of the features of the maize Sh1 gene, including a long leader intron and evidence of two polyadenylation sites. We compared sequences of the promoter region of Sus2 from 'Muntok Java,' a high sucrose S. officinarum x S. spontaneum hybrid, and 'PIN 84-1,' a low sucrose S. spontaneum. Their promoter regions were polymorphic primarily due to the presence of different large inserts ranging in size from 233 to 247 base pairs, which were identified as repetitive elements. The repetitive elements contain sequences that have been shown to be cis-acting regulatory elements in genes of other plants, and thus may differentially regulate the expression of Sus2 in different genotypes. Quantitative PCR was used to estimate gene copy number in different Saccharum species and showed four or more copies per basic number, suggesting ancient multiplication of the sugarcane genome, as has been hypothesized for maize and sorghum. Quantitative RT-PCR showed greater relative expression of Sus2 in PIN 84-1 than in Muntok Java. The promoter inserts, and a microsatellite in intron 14, may be useful molecular markers for identifying different Sus2 alleles.