Polygalacturonase required for degrading the pollen mother cell wall during microspore development. (1,4-alpha-D-galacturonosyl)n+m + H2O = (1,4-alpha-D-galacturonosyl)n + (1,4-alpha-D-galacturonosyl)m. Expressed in the tapetum cells in the anthers and in the ovules of open flowers. Transiently expressed during the early microspore stage. The mature pollen grains are arranged in a tetrad. A layer of material is frequently deposited on the surface of the distal region of the pollen grains. Belongs to the glycosyl hydrolase 28 family.