Abstract
Mitogen-activated protein kinases (MAPKs) form important signaling modules for a variety of cellular responses in eukaryotic cells. In plants, MAPKs play key roles in growth and development as well as in immunity/stress responses. Pollen-pistil interactions are critical early events regulating pollination and fertilization and involve many signaling events. Self-incompatibility (SI) is an important mechanism to prevent self-fertilization and inbreeding in higher plants and also is known to utilize signaling to achieve incompatible pollen rejection. Although several pollen-expressed MAPKs exist, very little is known about their function. We previously identified a pollen-expressed MAPK (p56) from Papaver rhoeas that was rapidly activated during SI; several studies implicated its role in signaling to SI-induced programmed cell death involving a DEVDase. However, to date, the identity of the MAPK involved has been unknown. Here, we have identified and cloned a pollen-expressed P. rhoeas threonine-aspartate-tyrosine (TDY) MAPK, PrMPK9-1 Rather few data relating to the function of TDY MAPKs in plants currently exist. We provide evidence that PrMPK9-1 has a cell type-specific function, with a distinct role from AtMPK9 To our knowledge, this is the first study implicating a function for a TDY MAPK in pollen. We show that PrMPK9-1 corresponds to p56 and demonstrate that it is functionally involved in mediating SI in P. rhoeas pollen: PrMPK9-1 is a key regulator for SI in pollen and acts upstream of programmed cell death involving actin and activation of a DEVDase. Our study provides an important advance in elucidating functional roles for this class of MAPKs.
Highlights
Mitogen-activated protein kinases (MAPKs) form important signaling modules for a variety of cellular responses in eukaryotic cells
Evidence Suggests That p56-MAPK Is Encoded by PrMPK9-1, an Ortholog of AtMPK9
We examined whether PrMPK9-1 was up-regulated after SI induction, as several MAPKs are up-regulated after stimulation, stress treatments (Zhang et al, 2014)
Summary
Mitogen-activated protein kinases (MAPKs) form important signaling modules for a variety of cellular responses in eukaryotic cells. Mitogen-activated protein kinases (MAPKs) form highly conserved signaling networks that are common to all eukaryotic cells, including animals, plants, and fungi. They are commonly used to Arabidopsis (Arabidopsis thaliana) has 20 MAPK genes, and there are a similar number in the sequenced genomes of other plant species. Many angiosperms face the possibility of self-fertilization and have evolved selfincompatibility (SI) to avoid this problem This is an important genetically controlled system that has evolved independently several times; several different mechanisms regulate SI in different plant species (for review, see Takayama and Isogai, 2005; Franklin-Tong, 2008). These allow recognition and rejection, so when male and female S-determinant allelic specificities match, self-(incompatible) pollen is recognized and rejected before fertilization can occur
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