Activation tagging of Arabidopsis POLYGALACTURONASE INVOLVED IN EXPANSION 2promotes hypocotyl elongation, leaf expansion, stem lignification, mechanical stiffening, and lodging

Summary Pectin is the most abundant component of primary cell walls in eudicot plants. The modification and degradation of pectin affects multiple processes during plant development, including cell expansion, organ initiation, and cell separation. However, the extent to which pectin degradation by polygalacturonases affects stem development and secondary wall formation remains unclear. Using an activation tag screen, we identified a transgenicArabidopsis thalianaline with longer etiolated hypocotyls, which overexpresses a gene encoding a polygalacturonase. We designated this gene asPOLYGALACTURONASE INVOLVED IN EXPANSION2(PGX2), and the corresponding activation tagged line asPGX2AT.PGX2is widely expressed in young seedlings and in roots, stems, leaves, flowers, and siliques of adult plants.PGX2‐GFPlocalizes to the cell wall, andPGX2ATplants show higher total polygalacturonase activity and smaller pectin molecular masses than wild‐type controls, supporting a function for this protein in apoplastic pectin degradation. A heterologously expressed, truncated version ofPGX2 also displays polygalacturonase activityin vitro. Like previously identifiedPGX1ATplants,PGX2ATplants have longer hypocotyls and larger rosette leaves, but they also uniquely display early flowering, earlier stem lignification, and lodging stems with enhanced mechanical stiffness that is possibly due to decreased stem thickness. Together, these results indicate thatPGX2 both functions in cell expansion and influences secondary wall formation, providing a possible link between these two developmental processes.