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

Abstract

Amyloses with distinct molecular masses are found in the starch of pea embryos compared with the starch of pea leaves. In pea embryos, a granule-bound starch synthase protein (GBSSIa) is required for the synthesis of a significant portion of the amylose. However, this protein seems to be insignificant in the synthesis of amylose in pea leaves. cDNA clones encoding a second isoform of GBSSI, GBSSIb, have been isolated from pea leaves. Comparison of GBSSIa and GBSSIb activities shows them to have distinct properties. These differences have been confirmed by the expression of GBSSIa and GBSSIb in the amylose-free mutant of potato. GBSSIa and GBSSIb make distinct forms of amylose that differ in their molecular mass. These differences in product specificity, coupled with differences in the tissues in which GBSSIa and GBSSIb are most active, explain the distinct forms of amylose found in different tissues of pea. The shorter form of amylose formed by GBSSIa confers less susceptibility to the retrogradation of starch pastes than the amylose formed by GBSSIb. The product specificity of GBSSIa could provide beneficial attributes to starches for food and nonfood uses.

Cloning and characterization of the granule-bound starch synthase�II gene in rice: gene expression is regulated by the nitrogen level, sugar and circadian rhythm

“…In waxy rice, while endosperm starch does not contain amylose, the starch fractions in the embryo, leaf blades, stems, and roots do contain amylose (Blakeney and Matheson 1984). Recent research has identified a new GBSS, designated GBSSII, in waxy wheat and amf pea, which is responsible for amylose synthesis in non-storage tissues Nakamura et al 1998;Vrinten and Nakamura 2000;Edwards et al 2002). Scheible et al (1997) reported that in tobacco, nitrate could be a signal that regulates starch synthesis by inhibiting the expression of the small subunit of ADPGlc pyrophosphorylase (AGPase) and decreasing the concentration of 3-phosphoglyceric acid (3PGA), the allosteric activator of AGPase.…”

Granule-bound starch synthase cDNA in Chlorella kessleri 11 h: cloning and regulation of expression by CO2 concentration

“…The eight conserved regions present in all plant GBSS (Cao et al 1999), were identified. Conserved regions 1 and 8 contain the KTGGL motif, which is considered to be the ADPglucose binding site (Furukawa et al 1993), and the KTGGL look-alike motif (Edwards et al 2002), respectively. The deduced amino acid sequence of the mature CkGBSS polypeptide shared higher identity with those of the GBSS from Chlamydomonas (65%) and Ostreococcus (59%) than with the GBSSI and GBSSII sequences of vascular plants (37-53%) (identities were obtained by BLASTP, in which N-and C-terminal ambiguous alignments were excluded).…”

“…In these mutants, amylose is not synthesized, and therefore, the starch granules are not stained blue-violet with iodine. Vascular plants have two GBSS isoforms, GBSSI which is involved in amylose synthesis in storage tissues (for review see Smith et al 1997) and GBSSII which is responsible for amylose synthesis in non-storage tissues such as leaves and stems (Denyer et al 1997;Fujita and Taira 1998;Nakamura et al 1998;Vrinten and Nakamura 2000;Edwards et al 2002;Dian et al 2003). …”

Genetic contributions to agricultural sustainability

“…There is evidence that other enzymes contribute to the synthesis of amylose, however GBSS is the only enzyme absolutely required for its synthesis (Ball & Morell 2003). There are separate GBSS genes expressed in endosperm and other parts of the plant providing a basis for observed differences in amylose content and structure between leaf and endosperm starches (Nakamura et al 1998;Edwards et al 2002).…”