Patterns of expansion and expression divergence in the plant polygalacturonase gene family

We found that both tandem and whole-genome duplications contribute significantly to the expansion of this gene family but are associated with substantial gene losses. In addition, there are at least 21 PGs in the common ancestor of Arabidopsis and rice. We have also determined the relationships between Arabidopsis and rice PGs and their expression patterns in Arabidopsis to provide insights into the functional divergence between members of this gene family. By evaluating expression in five Arabidopsis tissues and during five stages of abscission, we found overlapping but distinct expression patterns for most of the different PGs.Expression data suggest specialized roles or subfunctionalization for each PG gene member. PGs derived from whole genome duplication tend to have more similar expression patterns than those derived from tandem duplications. Our findings suggest that PG duplicates underwent rapid expression divergence and that the mechanisms of duplication affect the divergence rate.The functions and regulation of cell wall hydrolytic enzymes have intrigued plant scientists for decades. These enzymes cleave the bonds between the polymers that make up the cell wall, and include polygalacturonases (PGs), beta-1, 4-endoglucanases, pectate lyases, pectin methylesterases, and xyloglucan endo-transglycosylases [1]. As a consequence of their action, cell wall extensibility and cell-cell adhesion can be altered leading to cell wall loosening that results in cell elongation, sloughing of cells at the root tip, fruit softening, and fruit decay [2-4]. Cell separation processes also contribute to important agricultural traits such as pollen dehiscence and abscission of organs including leaves, floral parts, and fruits [5-7]. In addition, these enzymes are hypothesized to be involved in general housekeeping functions in plants [8].Among these hydrolytic enzymes, the PGs belong to one of the largest hydrolase families [9,10]. PG activities have been shown to be associated