Abstract
Starch structure strongly influences starch physicochemical properties, determining the end uses of starch in various applications. To produce starches with novel structure and exploit the mechanism of starch granule formation, an (engineered) 4, 6-α-glucanotransferase (GTFB) from Lactobacillus reuteri 121 was introduced into two potato genetic backgrounds: amylose-containing line Kardal and amylose-free mutant amf. The resulting starches showed severe changes in granule morphology regardless of genetic backgrounds. Modified starches from amf background exhibited a significant increase in granule size and starch phosphate content relative to the control, while starches from Kardal background displayed a higher digestibility, but did not show changes in granule size and phosphate content. Transcriptome analysis revealed the existence of a mechanism to restore the regular packing of double helices in starch granules, which possibly resulted in the removal of novel glucose chains potentially introduced by the (engineered) GTFB. This amendment mechanics would also explain the difficulties to detect alterations in starch fine structure in the transgenic lines.
Highlights
Starch, the most important source of calories in human diet, is the major storage carbohydrate in various photosynthetic tissues and storage organs
An glucanotransferase from Lactobacillus reuteri 121 (GTFB) gene from Lactobacillus reuteri 121 was introduced into KD and amf potato plants, aiming to create liner α-1, 6-glycosidic linkages in amylopectin and amylose chains during starch biosynthesis, producing starches with novel structure and properties
The results presented showed that differences in starch structure between modified and control starches could not be detected, suggesting that expression of the GTFB in potatoes either does not introduce new chains with liner α-1, 6-glycosidic linkages into starches, or these are below detectable levels, or novel chains have been identified as an error and removed by endogenous hydrolases
Summary
The most important source of calories in human diet, is the major storage carbohydrate in various photosynthetic tissues and storage organs. Expression of heterologous genes in potato has proven to have great potential to modify starches in planta [1] These genes may have properties that are slightly different from their plant counterparts and create different or novel phenotypes. A 4,6-α-glucanotransferase from Lactobacillus reuteri 121 (GTFB) is a novel enzyme that can convert starch or starch hydrolysates into isomalto/maltopolysaccharides (IMMPs) [17] This enzyme can transfer the non-reducing glucose moiety of an α-1,4 glucan chain to the non-reducing end of another α -glucan through α-1,6 linkages, generating a linear chain with α-1,6 linkages [18,19]. The effects of the (engineered) GTFB on starch characteristics and starch biosynthetic pathway are presented and discussed
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