A comparative analysis of the plant cellulose synthase (CesA) gene family

CesA gents are believed to encode the catalytic subunit of cellulose syntha se. Identification of nine distinct CesA cDNAs from maize (Zea mays) has al lowed us to initiate comparative studies with homologs from Arabidopsis and other plant species. Mapping studies show that closely related CesA genes are not clustered but are found at different chromosomal locations in both Arabidopsis and maize. Furthermore, sequence comparisons among the CesA-ded uced proteins show that these cluster in groups wherein orthologs are often more similar than paralogs, indicating that different subclasses evolved p rior to the divergence of the monocot and dicot lineages. Studies using rev erse transcriptase polymerase chain reaction with gent-specific primers for six of the nine maize genes indicate that all genes are expressed to at le ast some level in all of the organs examined. However, when expression patt erns for a few selected genes from maize and Arabidopsis were analyzed in m ore detail, they were found to be expressed in unique cell types engaged in either primary or secondary wall synthesis. These studies also indicate th at amino acid sequence comparisons, at least in some cases, may have value for prediction of such patterns of gene expression. Such analyses begin to provide insights useful for future genetic engineering of cellulose deposit ion, in that identification of close orthologs across species map prove use ful for prediction of patterns of gene expression and may also aid in predi ction of mutant combinations that may be necessary to generate severe pheno types.