THE UBIQUITOUS PRESENCE OF EXOPOLYGALACTURONASE IN MAIZE SUGGESTS A FUNDAMENTAL CELLULAR FUNCTION FOR THIS ENZYME

Exopolygalacturonase (exoPG) is a pectin-degrading enzyme abundant in maize pollen. Using immunochemistry and in situ hybridization it is sh own that in addition to its presence in pollen, exoPG is also present in sporophytic tissues, such as the tapetum and mesophyll cells. The e nzyme is located in the cytoplasm of pollen and of some mesophyll cell s. In other mesophyll cells, the tapetum and the pollen tube, exoPG is located in the cell wall. The measurement of enzyme activity shows th at exoPG is ubiquitous in the vegetative organs. These results suggest a general function for exoPG in cell wall edification or degradation. ExoPG is encoded by a closely related multigene family. The regulatio n of the expression of one of the exoPG genes was analyzed in transgen ic tobacco. Reporter GUS activity was detected in anthers, seeds and s tems but not in leaves or roots of transgenic plants. This strongly su ggests that the ubiquitous presence of exoPG in maize is the result of the expression of different exoPG genes.