The isolation and characterization of partial cDNAs associated with In Vitro tracheary element formation

Differential Display provides a sensitive method for quickly isolating and cloning cDNAs with corresponding mRNA transcripts that are differentially expressed between two different tissues or cell t5rpes. This technique provided a means by which three cDNAs with corresponding transcripts that are strongly expressed in suspension cultures of Zinnia mesophyll cells differentiating into tracheary elements were isolated. One transcript (63.30) has similarity to the non-histone protein 2 high mobility group-like protein in yeast, and to ribosomal proteins from yeast and the PRL2 protein from A. thaliana. The 63.30 transcript was found to be expressed in newly forming tracheary elements and phloem fibers and is expressed in response to auxin and/or cytokinin. A second transcript (54.6) was also determined to be expressed in newly forming tracheary elements and phloem fibers and is expressed in response to auxin and/or cytokinin. The deduced protein sequence of the 54.6 transcript shares some similarity to membrane spanning domains and the voltage sensor domain of the alpha subunit of the dihydropyridine- sensitive voltage-dependent calcium channel isolated from rat aorta. A third cDNA was isolated and expression of the transcript was found in in vitro differentiating tracheary elements, but no expression was detected in any whole plant tissue. It is possible that this transcript is a very rare species or is a result of the stress of culturing. No similarities to this transcript were detected by searches of the Blast/NCBI databases.