MAP kinases in pollen

The male gametophyte of flowering plants has a highly regulated developmental programme to ensure efficient fertilization of the ovule and the faithful transmission of genetic material to the offspring. Cell cycle control mechanisms dictate the formation of the vegetative and generative (sperm) cells, while an increase in transcriptional/translational activity and the accumulation of stored proteins and mRNA is followed by a quiescent state at maturation. A switch to a new developmental programme occurs after the pollen tube lands on the stigma with the formation of the pollen tube, growth through the style, and subsequent fertilization. Apart from the internal control mechanisms involved in this developmental programme, pollen grains must cope with physical changes during development within the anther (desiccation) and subsequently during germination on the stigma (rehydration). The metabolic and structural changes that occur throughout these processes should require signaling mechanisms to co-ordinate the appropriate response, and recent data demonstrate the presence in pollen of an array of molecules belonging to diverse signalling pathways, including mitogen-activated protein (MAP) kinases. The role of MAP kinases in pollen is discussed in the context of the various developmental and physical changes that occur throughout pollen maturation and germination.