The contributions of sporophytic tapetum to pollen formation

Successful pollen formation is essential for plant reproduction. During anther development, microspore mother cells undergo meiosis to form tetrads. After being released from the tetrad, microspores develop into mature pollen. The tapetum is the innermost layer of anther somatic cells and forms a locule to provide nutrition, enzymes and pollen wall materials for microspore development. Based on the male sterile phenotype, many genes important for tapetum and pollen development have been cloned. In this review, we highlight the genetic pathway of DYT1-TDF1-AMS-MS188-MS1 which acts in tapetal development in Arabidopsis. We also compared this genetic pathway in different species such as Arabidopsis, rice and maize. Based on this pathway, we review recent findings and insights into the contribution of the tapetum to pollen formation at the molecular level. 1) Tapetum provides nutrition for microspore development. 2) Tapetum provides enzymes to dissolve pectin and callose to release microspores from tetrads. 3) Tapetum synthesizes precursors for pollen wall formation via different molecular pathways. 4) Tapetum provides precursors for pollen coat formation. 5) Tapetum provides small RNAs to regulate genic methylation in the germline cells.