Defective pollen meiosis in Arabidopsis due to combined arabinan and galactan insufficiency

The development of pollen is critical for seed plants and depends on precise cellular and molecular mechanisms. It is known that the cell wall plays a key role in the progression of pollen maturation. An earlier phase in pollen development is the meiosis of pollen mother cells (PMCs), a fundamental process for producing viable pollen grains. However, the significance of the cell wall during pre-meiosis processes has remained unclear. Pectin, a major component of the cell wall, accumulates abundantly in pollen. To investigate the significance of the cell wall during pre-meiosis and meiosis, we generated an arad1 gals2 gals3 triple mutant of Arabidopsis thaliana, lacking the genes responsible for normal synthesis of arabinan and galactan, which constitute the side chains of pectin. Although vegetative growth and cell wall properties were comparable in wild-type (WT) and arad1 gals2 gals3, the pollen development in the mutant failed during meiosis. Immunohistochemical analysis showed that pectic arabinan and galactan accumulated in WT PMCs before meiosis, but this was not observed in mutant PMCs. On the other hand, it was found that pistil development of WT and arad1 gals2 gals3 was comparable. These findings suggest that the transient accumulation of arabinan and galactan in PMCs before meiosis is crucial for pollen meiosis. We believe that this study is the first to demonstrate the critical role of cell wall components, specifically pectic arabinan and galactan, in the pre-meiosis processes of pollen development.