Death of a tapetum: A programme of developmental altruism

Tapetal death is essential for the provision of many molecules required for pollen development including nutrients, proteins, lipids and polysaccharides. The molecules contribute to microspore release and pollen-wall formation. The process is tightly regulated and interference usually results in male sterility. Cytoplasmic male sterility is often a consequence of tapetal dysfunction and abiotic stresses can interfere with tapetal development. Tapetal breakdown resembles apoptotic programmed cell death (PCD), being relatively rapid and involving cell shrinkage, DNA fragmentation and mitochondrial and cytoskeletal disintegration. It offers a useful system for identifying the molecular mechanisms underlying plant PCD. This review outlines the changes occurring in the developing tapetum and the genes regulating this development, including their possible relationship to the cell death program. Clues to the mechanisms underlying tapetal PCD are emerging and these are discussed. An understanding of these mechanisms has important implications for agriculture, specifically for the maintenance of pollen fecundity under conditions of environmental stress and in the production of hybrid seed. Degeneration of the tapetal cell wall and callose surrounding the tetrads occurs prior to other cytological changes associated with PCD and the breakdown products may elicit aspects of the cell death program. (C) 2009 Elsevier Ireland Ltd. All rights reserved.