Signalling by tips 1

1 Signalling by tips 1 José A Feijó, Sílvia S Costa, Ana Margarida Prado, Jörg D Becker 2 and Ana Catarina Certal 3 New molecules, including protein kinases, lipids and 4 molecules that have neurotransmitter activities in animals, 5 continue to be described as important players in tip6 growing cells. Transcriptomics is beginning to show that 7 the largest single class of genes expressed in pollen tubes 8 encode signal transducers, reflecting the necessity to 9 decode all of the different pathways that are associated 10 with tip growth. Many of these pathways may use common 11 intracellular second messengers, with ions and reactive 12 oxygen species emerging as two major common 13 denominators in many of the processes involved in tip 14 growth. These second messengers might influence the 15 actin cytoskeleton through known interactions with actin16 binding proteins. In turn, changes in the dynamic 17 properties of the cytoskeleton would define the basic 18 polarity events needed to shape and modify tip-growing 19 cells. 20