Abstract
The exine composing an outer wall of pollen grains is believed to be important for successful pollination because of its species-specific architecture. However, little is known either about the mechanism of exine formation or genes involved in it. We performed the screening of mutagenized Arabidopsis with SEM, and identified many mutants showing defective exine structure. Among them, kaonashi4 (kns4) mutant showed thin exine layer mainly due to the short baculae. It also showed low fertility and collapse of the whole structure of pollen grains. TEM observation revealed that the exine abnormality begins at the tetrad stage as an extremely thin primexine layer. The KNS4 gene encoding a protein which resembles beta-1,3-galactosyltransferase involved in glycan biosynthesis. There are 20 genes encoding similar protein in Arabidopsis, but their function is hardly understood. The KNS4 is specifically expressed in the tapetal cells at around tetrad stage and the KNS4 protein is localized in the Golgi apparatus. Our hypothesis is that the KNS4 functions in the Golgi apparatus of tapetal cell at tetrad stage and is involved in biosynthesis of the components of primexine.
