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Engineering of plants for improved fi bre qualities 161

platelet aggregation, thereby opening up the possibility of using such mat-
erials for the development of biomedical devices that are in regular contact
with blood.

7.5 Future trends

As indicated above, an increasing body of experimental work has demon-

strated that modifications in gene expression can change fibre cell wall

structure and properties in various fibre species. Currently, gene targets in

individual fibre species are chosen on the basis of what we have learned
about cell wall formation in other model species (e.g. Arabidopsis, poplar,
tobacco) and have, until fairly recently, concentrated mainly on genes
encoding enzymes involved in the biosynthesis of different cell wall poly-
mers. However, because the formation of cell walls involves not only bio-
synthesis, but also remodelling of cell wall polymers and their interactions
during development, the genes encoding plant cell wall enzymes responsi-
ble for such developmental changes also represent potential targets for
modifi cation (Aspeborg et al., 2005; Irshad et al., 2008; Pelloux et al., 2007;
Sloan et al., 2009). Interestingly, such genes have also been detected in fl ax
(Day et al., 2005b; Roach and Deyholos, 2008) and hemp (De Pauw et al.,
2007). More recently, information is also starting to emerge about the
‘developmental programmes’ associated with the formation of the second-
ary cell wall. For example, a number of studies have underlined the role of
MYB and NAC transcription factors in controlling both lignin biosynthesis
and secondary cell wall formation (Goicoechea et al., 2005; Ko et al., 2009;
Zhong et al., 2008). These studies suggest that certain transcription factors
are able to act as ‘master switches’ regulating the whole secondary cell wall
developmental programme by activating genes controlling the biosynthesis
of the main structural polymers (cellulose, lignin, hemicelluloses). In con-
trast, other transcription factors such as MYB58 and MYB63 appear to
function as specific transcriptional activators of lignin biosynthesis (but not

other secondary cell wall polymers) in Arabidopsis (Zhou et al., 2009). In
addition, other studies have indicated that some transcription factors can
also act as negative regulators of cell wall biosynthesis (Legay et al., 2007).
These results clearly show that targeted genetic modifications are capable

of modifying cell wall structure. The first challenge to successfully manipu-

lating fibre quality in economically important species is therefore to obtain
a better fundamental understanding of the various gene networks involved
in controlling cell wall formation in plants.
Secondly, it is necessary to obtain more complete data about the genetic

make-up (genomic data) of different fibre species. This is important since
cell wall structure is mainly under genetic control, and structural differences

(e.g. lignified versus non-lignified) mainly reflect differences in the genetic

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