Signaling Events in Pollen Acceptance or Rejection in the Arabidopsis Species

Abstract

The initial events of pollen-pistil interactions are fundamentally important in fl owering plants because they infl uence successful fertilization. These early events include the recognition of pollen grains through signaling events in the pistil that will lead to the acceptance of a compatible pollen grain or the rejection of an incompatible pollen grain. There has been much research into this fi eld in the Brassicaceae, as this family includes many agriculturally important crops such as canola, radish, turnip, and cabbage. However, this review focuses on what is known about the early pollen-pistil interactions in the experimentally tractable Arabidopsis genus, including Arabidopsis thaliana (a self-compatible species) and Arabidopsis lyrata (a self-incompatible species). Compatible pollinations are driven by the ability of the pistil to provide the resources for an acceptable pollen grain to hydrate, germinate, and fertilize the ovule. Self-incompatible species have a receptorligand signaling pathway that rejects self-pollen grains, preventing inbreeding and encouraging genetic diversity within the species. There is some overlap between these two pathways, and current research is looking for unknown elements and downstream events following the initial recognition of a pollen grain in Arabidopsis .

RNA silencing of exocyst genes in the stigma impairs the acceptance of compatible pollen in Arabidopsis

“…In Arabidopsis, pollen-pistil interactions trigger a cascade of complex events in stigmatic papillae that mediate the acceptance of compatible pollen and the rejection of self-incompatible pollen (for review, see Indriolo et al, 2014b). While considerable progress has been made in deciphering the cellular signaling regulating the rejection of self-incompatible pollen in the Brassicaceae (for review, see Iwano and Takayama, 2012;Dresselhaus and Franklin-Tong, 2013;Indriolo et al, 2014b), comparatively little is known about the cellular responses of stigmatic papillae to compatible pollen.…”

“…While considerable progress has been made in deciphering the cellular signaling regulating the rejection of self-incompatible pollen in the Brassicaceae (for review, see Iwano and Takayama, 2012;Dresselhaus and Franklin-Tong, 2013;Indriolo et al, 2014b), comparatively little is known about the cellular responses of stigmatic papillae to compatible pollen. Previously, we have demonstrated that EXO70A1 is an essential factor in the stigma for compatible pollen-pistil interactions in Arabidopsis and B. napus promoting pollen hydration and pollen tube penetration into the stigma surface (Samuel et al, 2009;Safavian et al, 2014).…”

“…Communication is initiated rapidly following contact of a pollen grain with a stigmatic papilla, as the role of the papillae is to regulate the early cellular responses leading to compatible pollen germination. The basal compatible pollen recognition response also presents a barrier to foreign pollen or is inhibited with self-incompatible pollen (for review, see Dickinson, 1995;Hiscock and Allen, 2008;Chapman and Goring, 2010;Indriolo et al, 2014b).…”

“…Two stigmaspecific Brassica oleracea glycoproteins, the S-Locus Glycoprotein and S-Locus Related1 (SLR1) protein, play a role in compatible pollen adhesion (Luu et al, 1997(Luu et al, , 1999, potentially through interactions with the pollen coat proteins, PCP-A1 and SLR1-BP, respectively (Doughty et al, 1998;Takayama et al, 2000). The simultaneous recognition of self-incompatible pollen would also take place at this stage (for review, see Dresselhaus and Franklin-Tong, 2013;Indriolo et al, 2014b;Sawada et al, 2014). Thus, this interface not only provides a strengthened bond between the pollen grain and stigmatic papilla, but likely facilitates the interaction of signaling proteins from both partners to promote specific cellular responses in the stigmatic papilla toward the pollen grain.…”

The Arabidopsis KINβγ Subunit of the SnRK1 Complex Regulates Pollen Hydration on the Stigma by Mediating the Level of Reactive Oxygen Species in Pollen

“…During the interactions between the pollen and stigma, a series of events occur in succession, including pollen adhesion onto the stigma, pollen hydration and germination, and the polarized growth of pollen tubes across stigmatic tissue. In recent years, the interactions between the pollen and stigma have been studied in a number of plant species [ 3 , 4 ]. However, determining the mechanisms underlying these interactions remains a major challenge.…”