Question: You want to reduce the level of lignin in plants making them easier to digest, but could this reduce their ability of grow properly?, and could this reduce the yeild?

Yvette Wilson answered on 22 Jun 2010:

yeah! that’s the bit that I left out of my description:-) Good question. So-o-o the lignin pathway starts off with a common molecule that all organisms have. There are then 10 enzymes that opperate sequentially to modify the molecule to get a lignin unit (lignin units then bind together and with sugar in the cell wall). there are three main different lignin ‘units’ – ie different molecules that have different binding properties.

The molecules that are formed during the beginning of the pathway are used by the plant for signalling and disease resistance and if you interfere with the ‘early-acting’ enzymes you get less lignin – both of these effects drastically alter the plant’s growth so thats not much use. So far studies of trees have shown that if you interfere with later acting enzymes you get the same amount of lignin, but you change the lignin *units* that are made and you interfere with how the lignin binds together and how it binds to the sugars in the cell wall. In these cases there is little evidence of altering the plant’s growth/yield and it is easier to release sugars.

Saying all that – just about everything that is known about the lignin pathway is from either gymnosperms or dicotyledon species ie different evolutionary lineages from monocotyledons (the cereals). So far we have found evidence that the same enzymes exist in the cereals (using barley) so the pathway is likely to be similar so several of my colleagues are looking at what happens when you interfere with the later-acting enzymes.

It gets even more complicated I’m afraid….we’ve also found that there are several genes in barley that make the same enzyme, its possible that these different genes are active in different circumstances so maybe just stopping one of the several will give you less/weaker lignin in the straw specifically without changing the plant too much.

A large part of our work is therefore not only to identify mutations in genes that make less lignin, but also carry out a lot of experiments to make sure that nothing else is changed.

…sorry if that’s far too much information…and maybe drop a comment if it makes absolutely no sense!