Manipolazione genetica della composizione dell'amido
Author(s)
Sestili, Francesco
Date Issued
March 14, 2008
Type
Doctoral Thesis
Abstract
Wheat plays an important role in the food industry where is used for the production of a vast array of foods
which are a regular part of human diet, as bread, pasta, noodles, biscuits, rolls, breakfast cereals, cookies and
cakes.
Starch, which accounts for 65-75% of wheat grain dry weight, is the major constituent of flour and semolina
and strongly affects their functionality. Reserve starch is composed of two types of polymers, amylose and
amylopectin. Amylose is a linear polymer that constitutes about 30% of total starch, whereas amylopectin
has a branched structure and constitutes the remaining starch.
A class of starch synthase (Granule Bound Starch Synthase: GBSSI) is involved in amylose synthesis, while
the amylopectin is produced by the concerted action of starch synthases (SSI, SSII, SSIII), branching (BEs
IIa, BEs IIb and BEs I) and debranching enzymes (DBEs).
The possibility to manipulate starch composition in cereals, and in wheat in particular, is receiving an
increased attention, due to the recognition of its important role in food and non food applications.
Starch can be used as a basic material for the production of non-food products in paper, plastic, adhesive,
textile, medical and pharmaceutical industry.
At present the researchers are focusing on high amylose starches because derived foods have an increased
amount of resistant starch, which has been shown to have beneficial effects on human health. The
nutritionists believe that the resistant starch has a role similar to dietary fibre inside the intestine, protecting
against diseases as colon cancer, type II diabetes, obesity and osteoporosis.
Moreover, pasta produced with semolina containing higher amylose content shows good cooking resistance
and firmness, satisfying consumer preferences.
Low amylose starches can be used for the production of higher quality noodles and frozen foods,
additionally, they have positive impact on food shelf life.
In this work different approaches in order to modify starch composition have been undertaken.
In particular, a set of partial and complete waxy mutants of durum and bread wheat has been characterized
by evaluating the effect of the single waxy genes on amylose synthesis, starch structure, composition and
flour qualitative characteristics. Wx-B1 allele has resulted to be the most powerful gene controlling the
amylose synthesis; moreover, a compensation mechanism seems to be present in partial waxy durum lines,
with the functional waxy gene compensating for the lack of other allele.
In order to obtain high amylose lines of bread and durum wheat, different strategies have been used.
The first approach has been the identification and utilization of natural or induced mutants in the genes
encoding the starch synthases SSII (also known as Sgp-1). Several mutations in Sgp-1 genes have been
identified by TILLING and SDS-PAGE analysis on a mutagenized population of bread wheat.
The second strategy has consisted in the production of durum wheat lines overexpressing a waxy gene and
the silencing of genes encoding branching enzymes of class IIa (BEIIa) using transgenic approaches. The
overexpression of Wx-B1 gene doesn’t affect amylose content and starch properties.
SBEIIa genes have been silenced by RNA interference in two different durum wheat cultivar (Svevo e
Ofanto), using the biolistic and agrobacterium approaches.
Additional information
Dottorato di ricerca in Biotecnologie vegetali
Subjects
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