Abstract
The outmost surface of mature pollen grains is covered with an architecture, called exine. It has extremely diversed structures among higher plant species, and plays important roles in plant reproduction, for example, protection of male gametes and pollen recognition by papilla cells. However, little is known about the mechanism of exine construction. kns7 mutant, isolated by screening of EMS-mutagenized Arabidopsis, showed a defect in reticular structure of wild-type exine. Observation of the exine formation process using auramine O revealed that the defect in kns7 appeared very early stage of exine formation. Heterozygotes of kns7 had pollen grains with normal exine structure, indicating that KNS7 gene is expressed in diploid cells, such as pollen mother cells and tapetal cells. The exine development is believed to occur by deposition of sporopollenin, the main component of exine, to probacula, the backbone of exine. Thus, we predict that KNS7 is involved in the biosynthesis or secretion of sporopollenin, or probacula formation. Map-based cloning enabled us to identify the candidate gene of KNS7.
