Page 178 - Advances in Textile Biotechnology

Engineering of plants for improved fi bre qualities 159

bundles and surrounding stem cells, as well as between individual fi bre cells.

In an attempt to facilitate retting, flax plants were engineered to naturally
produce fungal pectinases (polygalacturonase and rhamnogalacturonase)
that were hypothesized to weaken the pectin-rich intercellular layers
(Musialak et al., 2008). Subsequent analyses showed that engineered plants
contained reduced amounts of pectin and showed a greater than two-fold

increase in retting efficiency compared with non-modified plants. In con-

trast, no changes were observed in either lignin or cellulose content. Inter-
estingly, modified plants also appeared to be more resistant towards

F. culmorum and F. oxysporum, possibly in relation with the observed
increase in soluble phenolic levels.

7.4.3 Introduction of novel properties

In addition to modifying fibre quality by targeting native cell wall polymers

such as lignin, fibre plants have also been engineered to produce polymers
that are not normally produced by plants. For example, genes coding PHB
(poly-β-hydroxybutyrate) synthesis were introduced into cotton plants by
particle bombardment (John and Keller, 1996). PHB is a hydrophobic and
thermoplastic agent displaying physical and chemical properties similar to
those of polypropylene and is naturally produced by bacteria as a source
of carbon and energy (Bohmert et al., 2000). In this study, eight engineered
plants (Gossypium hirsutum L. cv DP50) were shown to contain both phbB
and phbC genes, and the presence of PHB in the cytoplasm of transgenic

cotton fibres was confirmed by electron microscopy and HPLC, GC and

MS analysis. Although the amount of PHB in the cotton fibres was very low

(0.34% fibre weight), it influenced the thermal properties of fi bres. The rates

of cooling and heat uptake were lower in engineered fibres than in unmodi-

fied cotton fibres. Interestingly, the degree of modification appeared to be
correlated with the PHB content of the different plants examined, thereby
suggesting that improved thermal properties (for example in winter cloth-
ing) could be obtained by increasing PHB content.
A similar strategy has also been used to increase the elastic properties of
fl ax fi bres (Wróbel et al., 2004, Wróbel-Kwiatkowska et al., 2007b). In these
studies, three bacterial genes (phbA, phbB, phbC) encoding different
enzymes of the PHB biosynthetic pathway were introduced into fi bre fl ax
(L. usitatissimum L. cv Nike) by Agrobacterium. Analyses of modifi ed plants
showed that although PHB synthesis was not associated with major distur-
bances in growth or fertility as previously observed in Arabidopsis (Kourtz

et al., 2007), it did give rise to a slight decrease in straw and fibre yield of
engineered plants. Nevertheless, the engineered plants also showed increased
retting effi ciency and signifi cant improvements in stem mechanical proper-
ties. In addition, technical analyses of fibres obtained from fi eld-grown

© Woodhead Publishing Limited, 2010