Wheat Granule-Bound Starch Synthase I and II Are Encoded by Separate Genes That Are Expressed in Different Tissues

Abstract

Studies of waxy mutations in wheat and other cereals have shown that null mutations in genes encoding granule-bound starch synthase I (GBSSI) result in amylose-free starch in endosperm and pollen grains, whereas starch in other tissues may contain amylose. We have isolated a cDNA from waxy wheat that encodes GBSSII, which is thought to be responsible for the elongation of amylose chains in non-storage tissues. The deduced amino acid sequences of wheat GBSSI and GBSSII were almost 66% identical, while those of wheat GBSSII and potato GBSSI were 72% identical. GBSSII was expressed in leaf, culm, and pericarp tissue, but transcripts were not detected in endosperm tissue. In contrast, GBSSI expression was high in endosperm tissue. The expression of GBSSII mRNA in pericarp tissue was similar at the midpoints of the day and night periods. The GBSSII genes were mapped to chromosomes 2AL, 2B, and 2D, whereas GBSSI genes are located on group 7 chromosomes. Gelblot analysis indicated that genes related to GBSSII also occur in barley, rice, and maize. The possible role of GBSSII in starch synthesis is discussed.Starch is composed of two distinct polymers; amylopectin, which consists of long chains of (1-4)-linked ␣-Dglucopyranosyl units with extensive branching resulting from (1-6) linkages, and amylose, which is a relatively linear molecule of (1-4)-linked ␣-d-glucopyranosyl units (Whistler and Daniel, 1984). Both types of chains are elongated by starch synthases that transfer ␣-d-Glc from ADPGlc to the growing chain, and specific starch synthases are active in the synthesis of each type of polymer. Whereas a number of starch synthases are thought to catalyze amylopectin synthesis (Dry et al

Starch accumulation, activities of key enzyme and gene expression in starch synthesis of wheat endosperm with different starch contents

“…Gel-blot analysis indicated that genes related to GBSSII also occur in barley, rice, and maize. The possible role of GBSSII in starch synthesis is discussed (Vrinten and Nakamura 2000). Our study indicated that the change trend of high starch content, E8 and low starch content, Annong9912 were similar, and the expression of GBSS-I and GBSS-II genes exhibited significant different profiles during wheat endosperm development (Fig.…”

Spatiotemporal Profiling of Starch Biosynthesis and Degradation in the Developing Barley Grain

“…2B; noted also by Patron et al, 2002). Similarly, the ortholog GBSSII in wheat is expressed in pericarp and embryo as well as in vegetative organs (Vrinten and Nakamura, 2000). Based on the expression patterns in wheat, we assume that GBSS1b is also expressed in barley leaves, contributing there to amylose biosynthesis, while GBSS1a is a major enzyme involved in amylose synthesis in endosperm.…”

Discrete Forms of Amylose Are Synthesized by Isoforms of GBSSI in Pea[W]

“…One class consists entirely of GBSSI from monocots. The second class includes all of the GBSSI forms from dicots and one isoform from wheat, GBSSII, which is expressed in leaves (Vrinten and Nakamura, 2000). This second class is subdivided, with the pea embryo GBSSIa clustering with the GBSSI from another legume, bean.…”

“…A protein of similar molecular mass, antigenic properties, and N-terminal sequence to GBSSI has been detected in the leaves of lam pea , and a cDNA encoding a GBSSI-like starch synthase has been isolated from waxy wheat and shown to be expressed in nonstorage tissues (Fujita and Taira, 1998;Nakamura et al, 1998;Vrinten and Nakamura, 2000).…”