Fruit firmness

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Fruit Firmness (Stewart Dalton, Spring 2013)

-Fruit softening is associated with cell wall disassembly. During ripening some of the most apparent changes that occur to the cell wall are that to the pectin component of the cell wall. This finding suggests that the enzymes involved with the degradation of pectin are some of the most important in the loss of fruit firmness. File:Pectatelyases.pdf

-Softening occurs with enzymatic digestion of cell wall components such as pectin, cellulose and hamicellulose. http://hortsci.ashspublications.org/content/37/2/386.full.pdf


-A good paper on cell wall degradation: File:Cellwalldestruction.pdf

-Pectin decreases as blueberries ripen from green to to blue- degradation of the cell wall and middle lamella is directly responsible for the loss of firmness in ripening fruits.

-Middle lamella, contains a great deal of pectin. Important to fruit firmness: Middlelamella.gif

-Fruit firmness is an important economic trait in blueberries for many reasons.

-Expansin protein family- necessary for softening process. Expression of expansin mRNA and protein is correlated with growth and/or cell wall disassembly (Dotto et al, 2005)File:StrawFirmness1.pdf

-Expansin protein family website: http://genomebiology.com/2005/6/12/242

-Expansin protein from NCBI: http://www.ncbi.nlm.nih.gov/protein/AAC63088.1 and http://www.ncbi.nlm.nih.gov/gene/843288

-It is believed that the alpha-expansin gene Le-ESP1 plays a role in fruit softening: its over expression leads to softer fruit texture while its under expression leads to firmer fruits. File:Expansinreview.pdf


-pectate lyase gene expression causes softening in strawberries. It was seen that experimental transgenic strawberries had lower amounts of ionically bound pectins that control fruit. The pectate lyase gene is an excellent candidate for biotechnological improvement of fruit softening in the strawberry (and maybe the blueberry also!). Rapid postharvest softening is the primary reason for strawberry's short self life. Softening occurs via the degradation of the middle lammella of cortical parenchyma cells. Ripe fruits have thinner cell walls and show a loss of intercellular material. The underlying biochemical mechanism of strawberry softening is unclear. Percentage of water soluble pectins increases in ripe fruit but total quantity of polyuronide residues and polyuronide length are only slightly modified. Low poligalacuturonase activity found in ripe fruit. Degradation of the cellulose matrix is a major factor in loss of fruit firmness. Endoglucanase activity increases in ripening strawberries. The pectate lyase gene is a candidate for pectin degradation, which leads to loss of fruit firmness. Pectin lyase degrades pectins via a B-elimination reaction in contrast to the hydrolytic mechanism of polygalacturonases. File:Pectatelyasegene.pdf

-Pectins are broken down by pectinases. A list of different pectinases:

-pectin esterase (EC 3.1.1.11) http://www.ncbi.nlm.nih.gov/protein/82097 and http://www.ncbi.nlm.nih.gov/gene/820651 (Tomato)

-polygalacturonase (EC 3.2.1.15) http://www.ncbi.nlm.nih.gov/protein/AAA34177.1 and http://www.ncbi.nlm.nih.gov/gene/839391 (Tomato)

-pectate lyase (EC 4.2.3.2) http://www.ncbi.nlm.nih.gov/protein/AEE74778.1 and http://www.ncbi.nlm.nih.gov/gene/838004 (Arabidopsis)

-pectin lyase (EC 1.4.2.10) http://www.ncbi.nlm.nih.gov/gene/816922 (Arabidopsis)

[1]

-Alteration of the cell wall and middle lamella of fruits is responsible for textural changes during development and postharvest storage. Polysaccharides such as pectin, cellulose and hemicellulose are major components of the cell wall and undergo depolymerization in maturing fruit. This depolymerization contributes significantly to the softening of fruit tissue. Pectin is the predominant component of the middle lamella which is depolymerized during ripening. File:Pectintransistion.pdf

-A list of blast results from arabidopsis for the enzyme family of pectinases: http://harvester.kit.edu/harvester/arabidopsis/IPI00522/IPI00522605/tabID_3.html

-Carbohydrate-Active Enzyme database: http://www.cazy.org/

-Status Report: File:Statusreport.pptx

-Questions: Are there any other important proteins involved in the break down of the cell wall and/or middle lamella? In what pathway are these proteins involved? What are some transcription factors or triggers that activate these proteins?

-List of pectate lyase proteins from Arabidopsis [[porgn%3A__txid3702]

-List of expansin proteins from Arabidopsis [[2]]