A mutant rice line is discovered, which has increased straw digestibility and si

Question

A mutant rice line is discovered, which has increased straw digestibility and significantly lower levels of ferulic acid in its cell walls.

a) What is ferulic acid?

b) Why would lower levels of ferulic acid increase straw digestibility at the molecular level?

The causative mutation is mapped to a gene that encodes a glycosyl transferase family 61 enzyme.

c) Explain how loss of function in a glycosyl transferase might result in decreased ferulic acid content.

d) Why would you expect a similar mutation not to have the same effect in dicot plants?

Explanation / Answer

a) Ferulic acid is a phenolic acid that occurs as an ester on arabinosyl residues on arabinoxylan polymers in grass cell walls.

b) Arabinoxylans form the major hemicellulose (matrix polysaccharide) in the cell walls of grasses and the feruloyl esters can dimerise to form crosslinks within this polymer and also form the sites of covalentn linkage with lignin forming crosslinks that make the cell wall harder to access by digestive enzymes.

c) GT61 enzymes are involved in adding arabosyl and xylosyl side chains to arabinoxylans, and decreased arabinosyl side chains can lead to decreased ferulic acid content as there are fewer sites for the addition of feruloyl esters

d) Because dicot xylans do not have arabinosyl residues or feruloyl esters

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