A search of the GenBank database revealed that this gene has a very high similarity with the cotton celA and Arabidopsis cellulose synthase genes. There are two hypervariable regions in the plant genes. The first is found at the amino terminus and covers the first 211 amino acids of Pxcel1. The second, described in Pear et al. Northern blot analyses indicate that Pxcel1 is highly expressed in differentiating xylem.
Transcripts are barely detectable in leaves and phloem.
From a genomic Southern blot we estimate there are four or five copies of the gene in the poplar genome. We have isolated three different partial cDNA clones that contain a few amino acids different from those in Pxcel1. We also wish to thank Mr. Eun-Gyu No for many useful suggestions. A Populus tremula x P. alba xylem cDNA library was differentially screened using cDNA probes derived from phloem, leaf and differentiating xylem mRNAs respectively. The clone was picked from those with transcripts unique to xylem or with levels high in xylem but very low in the other two tissues.