Abstract
The exine, an outermost wall of pollen grains, is believed to play an important role for successful pollination. However, little is known about the exine formation mechanism based on molecular genetics. The pollen grains of Arabidopsis kaonashi4 (kns4) mutant isolated by our screening for exine-defective mutants displayed remarkably thin exine layer. They also showed low fertility and abnormal entire morphology. Histological analysis revealed that abnormal development of pollen mother cells (PMCs) and poor primexine formation in tetrads occurs in kns4. The KNS4 gene encodes a protein having high homology with animal β-1,3-galactosyltransferase. Biochemical analysis using Yariv reagents indicated that the amount of arabinogalactan proteins (AGPs) in tetrads is reduced in kns4. The co-localization analysis showed the probability that KNS4 protein is localized in the Golgi apparatus. We hypothesized that the KNS4 is required in the Golgi of PMCs and/or tapetal cells for the biosynthesis of AGPs, which are abundant in primexine. Experiments to determine the expression profile of KNS4 are in progress.
