Deficiency of maize starch-branching enzyme i results in altered starch fine structure, decreased digestibility and reduced coleoptile growth during germination

Abstract

BackgroundTwo distinct starch branching enzyme (SBE) isoforms predate the divergence of monocots and dicots and have been conserved in plants since then. This strongly suggests that both SBEI and SBEII provide unique selective advantages to plants. However, no phenotype for the SBEI mutation, sbe1a, had been previously observed. To explore this incongruity the objective of the present work was to characterize functional and molecular phenotypes of both sbe1a and wild-type (Wt) in the W64A maize inbred line.ResultsEndosperm starch granules from the sbe1a mutant were more resistant to digestion by pancreatic α-amylase, and the sbe1a mutant starch had an altered branching pattern for amylopectin and amylose. When kernels were germinated, the sbe1a mutant was associated with shorter coleoptile length and higher residual starch content, suggesting that less efficient starch utilization may have impaired growth during germination.ConclusionsThe present report documents for the first time a molecular phenotype due to the absence of SBEI, and suggests strongly that it is associated with altered physiological function of the starch in vivo. We believe that these results provide a plausible rationale for the conservation of SBEI in plants in both monocots and dicots, as greater seedling vigor would provide an important survival advantage when resources are limited.

Starch Biosynthesis in the Developing Endosperms of Grasses and Cereals

“…Indeed, physical interactions between SBEI and SBEIIb have been reported in endosperm amyloplasts from a number of sources [288][289][290][291]. SBEI's role in determination of amylopectin structure may be rather more subtle, as suggested by one recent study showing reduced germination efficiency of SBEI-deficient maize kernels [292]. This work suggests that SBEI somehow produces a granule structure that is more accessible to α-amylases produced in the aleurone layer for the degradation of starch reserves during germination.…”

“…In addition, ae − starch granules are deeply fissured and irregularly shaped [244,303]. Since SBEIIa is a minor component of SBE activity in the endosperm of maize and rice, its loss has relatively minor affects on endosperm starch [304,305], and it appears to play a more prominent role in transient starch synthesis in the chloroplast [292]. The ae − mutation in maize and rice produces a so called 'high-amylose' starch, which is characterized by long internal chain lengths of amylopectin, and less frequently branched outer chains compared with normal starches [306], leading to alterations in granule packing and a less ordered structure than wild-type [307].…”

Biosynthesis of Reserve Starch

“…5.7a), suggesting that BEI plays a part in the synthesis of intermediate and long chains (Satoh et al 2003). The situation is likely common among cereal endosperm (Yao et al 2004;Regina et al 2010;Butardo et al 2011;Liu et al 2012a), although the possibility that BEI also affects the position of branches of amylopectin in maize endosperm cannot be ruled out (Xia et al 2011).…”

Time Course of Starch Biosynthesis Enzymes Activity and Root Tuber Starch of Four Cassava Cultivars

“…Cassava root tuber SBE is also involved in the biosynthesis of amylopectin, however it is mainly to modify the fine structure of amylopectin (Xia et al, 2011). Although the cassava root tuber SBE activity of four cultivars oscillated during the growth period, the range was not too much ( Figure 6).…”