I. Engineering improved nutrition in seed-storage proteins
        A. problem- unbalanced essential amino acids in seeds
                -legumes- low in S-containing aa- cysteine and methionine
                -cereals- low in lysine, threonine, tryptophane

        B. Seed storage protein- major proteins in seed
                1. multiple forms within one species
                2. only produced in seed
                3. stored in protein bodies
                4. types:       -albumins:  water soluble
                                -prolamins: alchohol/water soluble
                                -globins:weak saline solution soluble

        C. Examples:
                1. albumins
                        -mostly in dicots
                2. Prolamins
                        -primarily in grasses
                        - internal repeats of amino acids, glutamine and proline rich
                                -S-rich- repeats in N-term
                                -S-poor- few cysteins
                                -High MW
                3. Globins
                        -in both monocots and dicots
                        -low in methionine and cysteine
                        -e.g legumins in legumes

        D. Modifications to improve quality
                1. Modify sequence of native storage protein
                2. Express another plant’s seed storage protein
                        -e.g. a. Brazil nut 2S albuminexpressed in tobacco and rape 
                                (33% more methionine)
                                  b. Phaseolin (Bean) expressed in rice

                3. Changing balance of native genes
                        -antisense of one form that is low in nutrition may enhance other 
                                form
                        -e.g. Rape seed
                                -cruciferin-12S albumin- 60% of protein
                                                 albumin- low in mthionine and cysteine
                                -napin- 2S albumin- higher met and cyst
                                -antisense of cruciferin gene- reduced cruciferin, increased 
                                                napin

II. Engineering gluten in wheat
        -gluten- a prolamin (1/2 of total protein) found in wheat
                -allows elasticity-needed for bread making
                -50 genes producing glutens

                -two types of prolamins- 
                        gliadins-provide viscosity
                        glutenins- -provide elasticity

        -Genetics- shows due to alleles at 2 genes in one locus on arms of 
                        chromosomes 1A, 1B, 1D
                -characterized from cloning of good and poor quality
                        -expression of protein
                        -more cysteins in better quality alleles

        -Improvements:
                -introduce high quality alleles
                -fine tune quality 
                        
 III. Fatty acid modification
        Oils quality affected by fatty acid consitituents
                major oils: Soy, sunflower, rapeseed
                                tropical- palm, coconut- high in saturated fatty acids

                -monounsaturated oils and plant sterols- prevent cholesterol
                                 absorption into intestines

                -Rape seed- only 3-unsaturated fatty acid in plants
                        1)-problem: high erucic acid (22:1)- 45-55% 
                                -eruic acid  deposited in heart muscle in mice
                                -found mutant low in Eruic acid- controlled by two loci
                        2) in frying, linoleic acid(18:3) is oxidized- unpleasent smell 
                                engineering plants to produce high stearate and lower 
                                lineoleic acid

IV. Other compounds in foods
        -e.g Glucosinolates in Rape seed used for animal feed
                -Brassicas produce glucosinolates for protection
                        
                        R-C-S-glucose
                        ||                              R= amino acid
                        N-O-SO2OH

                -stored in cells
                - mascerasion releases myrosinase- takes off glucose, forms 
                                isothiocyanates, nitryls, thiocyanates
                -pungent odor and bite of mustard family
                -reduces use as protein supplement to animal feeds
                -genetics- 3 genes determine production
                -Arabidopsis as model- cloned the Gls gene from genome mapping.

Report on expressing HMW gluten in wheat

Web pages on golden rice- expressing vitamin A
 
 

Last revised: April 7, 1998- Straney