Expression patterns of the gene encoding starch branching enzyme II in the storage roots of cassava (Manihot esculenta Crantz)

Abstract Spatial and temporal expression patterns of the sbeII and sbeI genes, encoding starch branching enzyme II and I, respectively, in cassava ( Manihot esculenta Crantz) were studied at different phenological stages of the crop. A partial cDNA for sbeII in cassava was cloned and used along with a cDNA-specific fragment of sbeI. As the cassava plant aged, the transcriptional activity of the sbeII and sbeI genes in the underground storage roots increased, whereas the activity in other organs remained the same or declined. At 180 days after planting (d.a.p.), levels of sbeII and sbeI transcripts in storage roots were very low, whereas at 360 d.a.p., the levels had increased dramatically. The 360 d.a.p. old storage roots also accumulated gbssII and gbssI transcripts, as well as a longer gbssI transcript, gbssI′. The difference between the gbssI and gbssI′ transcripts was shown to be due to differential splicing, whereby the gbssI′ transcript retained the first three introns. Unexpectedly, expression of sbeII and sbeI in the 360 d.a.p. storage roots exhibited fluctuations during the 24 h cycle, both under the normal light/dark regime and under continuous light or continuous dark conditions.