Differential expression of a polygalacturonase gene family in Arabidopsis thaliana

By systematic sequencing of a flower bud cDNA library from Arabidopsis thal iana, we have identified four cDNAs encoding polygalacturonase. The corresp onding genes, together with seven other A. thaliana genes present in the da tabases, form a small gene family. Sequence comparisons of the deduced poly peptides within the gene family or with other plant polygalacturonases allo w classification of the genes into different clades. Five polygalacturonase s, including all those isolated from the flower buds, are closely related t o the enzyme in pollen. Of the six remaining polygalacturonases, three are more closely related to the abscission-specific type of enzyme and two othe rs to the fruit polygalacturonase. The last one is more distantly related t o the others and might correspond to a new type of polygalacturonase. Expre ssion of the different genes was analysed on Northern blots and by a PCR-ba sed strategy. Results indicate that if, as expected, the cDNAs isolated fro m the flower bud library are strongly expressed in pollen, other genes are expressed at a low level in young developing tissues, such as in seedlings and roots, suggesting that they could be implicated in the cell wall modifi cations observed during cell elongation and/or expansion which occur in the se tissues.