Differential expression of cell-wall-related genes during the formation oftracheary elements in the Zinnia mesophyll cell system

Plants, animals and some fungi undergo processes of cell specialization suc h that specific groups of cells are adapted to carry out particular functio ns. One of the more remarkable examples of cellular development in higher p lants is the formation of water-conducting cells that are capable of suppor ting a column of water from the roots to tens of metres in the air for some trees. The Zinnia mesophyll cell system is a remarkable tool with which to study this entire developmental pathway in vitro. We have recently applied an RNA fingerprinting technology, to allow the detection of DNA fragments derived from RNA using cDNA synthesis and subsequent PCR-amplified fragment length polymorphisms (cDNA-AFLP), to systematically characterize hundreds of the genes involved in the process of tracheary element formation. Buildi ng hoops of secondary wall material is the key structural event in forming functional tracheary elements and we have identified over 50 partial sequen ces related to cell walls out of 600 differentially expressed cDNA fragment s. The Zinnia system is an engine of gene discovery which is allowing us to identify and characterize candidate genes involved in cell wall biosynthes is and assembly.