PRX9 and PRX40 are extensin peroxidases essential for maintaining tapetum and microspore cell wall integrity during Arabidopsis anther development

Pollen and microspore development is an essential step in the life cycle of all land plants that generate male gametes. Within flowering plants, pollen development occurs inside of the anther. Here, we report the identification of two class III peroxidase-encoding genes, PRX9 and PRX40, that are genetically redundant and essential for proper anther and pollen development in Arabidopsis thaliana. Arabidopsis double mutants devoid of functional PRX9 and PRX40 are male-sterile. The mutant anthers display swollen, hypertrophic tapetal cells and pollen grains, suggesting disrupted cell wall integrity. These phenotypes ultimately lead to nearly 100%-penetrant pollen degeneration upon anther maturation. Using immunochemical and biochemical approaches, we show that PRX9 and PRX40 are likely extensin peroxidases that contribute to the establishment of tapetal cell wall integrity during anther development. This work identifies PRX9 and PRX40 as the first extensin peroxidases to be described in Arabidopsis and highlights the importance of extensin cross-linking during plant development.