Identification and characterization of Arabidopsis thaliana genes involved in xylem secondary cell walls

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Abstract
The xylem of higher plants offers support to aerial portions of the plant body and serves as conduit for the translocation of water and nutrients. Terminal differentia- tion of xylem cells typically involves deposition of thick secondary cell walls. This is a dynamic cellular process accompanied by enhanced rates of cellulose deposition and the induction of synthesis of specific secondary-wall matrix polysaccharides and lignin. The secondary cell wall is essen- tial for the function of conductive and supportive xylem tissues. Recently, significant progress has been made in identifying the genes responsible for xylem secondary cell wall formation. However, our present knowledge is still insufficient to account for the molecular processes by which this complex system operates. To acquire further informa- tion about xylem secondary cell walls, we initially focused our research effort on a set of genes specifically implicated in secondary cell wall formation, as well as on loss-of- function mutants. Results from two microarray screens identified several key candidate genes responsible for sec- ondary cell wall formation. Reverse genetic analyses led to the identification of a glycine-rich protein involved in main- taining the stable structure of protoxylem, which is essential for the transport of water and nutrients. A combination of expression analyses and reverse genetics allows us to sys- tematically identify new genes required for the develop- ment of physical properties of the xylem secondary wall.