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Session 5 – Plant Development, Metabolism and Physiology
S5.6- Inducible xylem differentiation in Brachypodium
Elene R. Valdivia, María Teresa Herrera, Cristina Gianzo, Gloria Revilla, Ignacio Zarra y
Javier Sampedro
Departamento de Fisiología Vegetal, Facultad de Biología, Universidad de Santiago de
Compostela
elenevaldivia@gmail.com
Abstract
The manipulation of secondary cell wall composition in biomass crops is one of the most
promising strategies to reduce the processing cost of lignocellulosic materials, which
could then become an abundant source of cheap biofuels. Grasses are good
candidates for this approach, but very little is known about the regulation of grass cell
wall synthesis.
In the dicot Arabidopsis several of the transcription factors (TFs) involved in secondary
cell wall synthesis have been characterized in detail. In particular, VND genes seem to
act at very early stages of xylem differentiation and the expression of some of the VNDs is
sufficient to start the process of secondary cell wall deposition. We have identified and
cloned Brachypodium orthologs of the Arabidopsis VNDs. When three of these genes
(VND2, VND4 and VND5) are overexpressed transiently in tobacco leaves, they are
capable of inducing transdifferentiation into tracheary elements suggesting a
conservation of function.
Brachypodium can be transformed with high efficiency through cocultivation of
embryogenic calli with Agrobacterium. We have adapted the estradiol inducible system
for use in Brachypodium and have transformed this species with inducible overexpression
constructs for VND2, VND4 and VND5, as well as chimeric respressors obtained from the
same genes by addition of a repressor domain. Inducible overexpression of VND5 results
in extensive transdifferentiation of different cell types into tracheary element. Through RT-
PCR we have detected an increase expression of cellulose synthase, as well as some TFs
that could work downstream of the VND genes. We are currently characterizing this
plants which could provide a first draft of the regulatory network of secondary cell wall
synthesis in grasses. The repressor lines will be characterized soon and could allow us to
identify feedback mechanisms that detect secondary cell wall alterations.
Keywords
Brachypodium, Secondary cell wall synthesis, Transcription Factors
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