The Peroxin Loss-of-Function Mutation abstinence by mutual consent Disrupts Male-Female Gametophyte Recognition

Abstract

In eukaryotes, fertilization relies on complex and specialized mechanisms that achieve the precise delivery of the male gamete to the female gamete and their subsequent union [1-4]. In flowering plants, the haploid male gametophyte or pollen tube (PT) [5] carries two nonmotile sperm cells to the female gametophyte (FG) or embryo sac [6] during a long assisted journey through the maternal tissues [7-10]. In Arabidopsis, typically one PT reaches one of the two synergids of the FG (Figure 1A), where it terminates its growth and delivers the sperm cells, a poorly understood process called pollen-tube reception. Here, we report the isolation and characterization of the Arabidopsis mutant abstinence by mutual consent (amc). Interestingly, pollen-tube reception is impaired only when an amc pollen tube reaches an amc female gametophyte, resulting in pollen-tube overgrowth and completely preventing sperm discharge and the development of homozygous mutants. Moreover, we show that AMC is strongly and transiently expressed in both male and female gametophytes during fertilization and that AMC functions in gametophytes as a peroxin essential for protein import into peroxisomes. These findings show that peroxisomes play an unexpected key role in gametophyte recognition and implicate a diffusible signal emanating from either gametophyte that is required for pollen-tube discharge.

Defects in Peroxisomal 6-Phosphogluconate Dehydrogenase Isoform PGD2 Prevent Gametophytic Interaction in Arabidopsis thaliana

“…As shown recently, NO production in peroxisomes depends on Pex7p-based import of a cryptic NO synthase (Corpas and Barroso, 2014b). In light of the amc mutant, in which defective peroxisomal import prevents fertilization between mutant gametophytes (Boisson-Dernier et al, 2008), similar results obtained with the pgd2 alleles clearly link OPPP reactions in peroxisomes to important steps during fertilization. Thus, sugar-derived NADPH production in peroxisomes seems to be needed to reach or maintain a critical threshold of NO and possibly also JA.…”

She's the boss: signaling in pollen tube reception

“…In addition, the abstinence by mutual consent (amc) mutant has both PT reception and synergid cell death defects when the mutation is present in both male and female gametophytes. This indicates that this peroxin gene may be necessary for cell death in both the PT and the synergid, perhaps by modulating the production of reactive oxygen species (ROS) [22]. On the other hand, ultrastructural analysis of fer embryo sacs indicate that the penetrated synergid displays electrondense material [23], which is typical of the degenerating synergid [24].…”

The Role of LORELEI in Pollen Tube Reception at the Interface of the Synergid Cell and Pollen Tube Requires the Modified Eight-Cysteine Motif and the Receptor-Like Kinase FERONIA

“…Loss of AUTO-INHIBITED Ca 2+ ATPASE9 (ACA9), which encodes a calcium efflux pump, results in some pollen tubes failing to discharge the sperm, even though they reach the synergid and arrest growth in the synergid cell; thus, aca9 tubes differ from triple myb mutant tubes in that they fail to coil and burst (Schiøtt et al, 2004). Interestingly, abstinence by mutual consent (amc) mutants show pollen tube reception defects only when an amc pollen tube encounters an amc female gametophyte, indicating that pollen tube reception requires interactions between the male and the female gametophyte and that both gametophytes share common signaling components (Boisson-Dernier et al, 2008).…”