Showing papers by "Daphne R. Goring published in 2014"

The ARC1 E3 Ligase Promotes Two Different Self-Pollen Avoidance Traits in Arabidopsis

Abstract: Flowering plants have evolved various strategies for avoiding self-pollen to drive genetic diversity. These strategies include spatially separated sexual organs (herkogamy), timing differences between male pollen release and female pistil receptivity (dichogamy), and self-pollen rejection. Within the Brassicaceae, these outcrossing systems are the evolutionary default state, and many species display these traits, including Arabidopsis lyrata. In contrast to A. lyrata, closely related Arabidopsis thaliana has lost these self-pollen traits and thus represents an excellent system to test genes for reconstructing these evolutionary traits. We previously demonstrated that the ARC1 E3 ligase is required for self-incompatibility in two diverse Brassicaceae species, Brassica napus and A. lyrata, and is frequently deleted in self-compatible species, including A. thaliana. In this study, we examined ARC1’s requirement for reconstituting self-incompatibility in A. thaliana and uncovered an important role for ARC1 in promoting a strong and stable pollen rejection response when expressed with two other A. lyrata self-incompatibility factors. Furthermore, we discovered that ARC1 promoted an approach herkogamous phenotype in A. thaliana flowers. Thus, ARC1’s expression resulted in two different A. lyrata traits for self-pollen avoidance and highlights the key role that ARC1 plays in the evolution and retention of outcrossing systems.

High humidity partially rescues the Arabidopsis thaliana exo70A1 stigmatic defect for accepting compatible pollen

Abstract: We have previously proposed that Exo70A1 is required in the Brassicaceae stigma to control the early stages of pollen hydration and pollen tube penetration through the stigmatic surface, following compatible pollination. However, recent work has raised questions regarding Arabidopsis thaliana Exo70A1’s expression in the stigma and its role in stigma receptivity to compatible pollen. Here, we verified the expression of Exo70A1 in stigmas from three Brassicaceae species and carefully re-examined Exo70A1’s function in the stigmatic papillae. With previous studies showing that high relative humidity can rescue some pollination defects, essentially bypassing the control of pollen hydration by the Brassicaceae dry stigma, the effect of high humidity was investigated on pollinations with the Arabidopsis exo70A1-1 mutant. Pollinations under low relative humidity resulted in a complete failure of wild-type compatible pollen acceptance by the exo70A1-1 mutant stigma as we had previously seen. However, high relative humidity resulted in a partial rescue of the exo70A1-1 stigmatic papillar defect resulting is some wild-type compatible pollen acceptance and seed set. Thus, these results reaffirmed Exo70A1’s proposed role in the stigma regulating compatible pollen hydration and pollen tube entry and demonstrate that high relative humidity can partially bypass these functions.

A conserved role for the ARC1 E3 ligase in Brassicaceae self-incompatibility.

Abstract: Ubiquitination plays essential roles in the regulation of many processes in plants including pollen rejection in self-incompatible species In the Brassicaceae (mustard family), self-incompatibility drives the rejection of self-pollen by preventing pollen hydration following pollen contact with the stigmatic surface Self-pollen is recognized by a ligand-receptor pair: the pollen S-locus cysteine rich/S-locus protein 11 (SCR/SP11) ligand and the pistil S receptor kinase (SRK) Following self-pollen contact, the SCR/SP11 ligand on the pollen surface binds to SRK on the pistil surface, and the SRK-activated signaling pathway is initiated This pathway includes the armadillo repeat containing 1 (ARC1) protein, a member of the plant U-box (PUB) family of E3 ubiquitin ligases ARC1 is a functional E3 ligase and is required downstream of SRK for the self-incompatibility response This mini review highlights our recent progress in establishing ARC1's conserved role in self-pollen rejection in Brassica and Arabidopsis species and discusses future research directions in this field

The ARC1 E3 Ligase Promotes a Strong and Stable Self-Incompatibility Response in Arabidopsis Species: Response to the Nasrallah and Nasrallah Commentary

Abstract: Following the identification of the male (S-locus Cysteine Rich/S-locus Protein 11) and female (S Receptor kinase [SRK]) factors controlling self-incompatibility in the Brassicaceae, research in this field has focused on understanding the nature of the cellular responses activated by these regulators. We previously identified the ARM Repeat Containing1 (ARC1) E3 ligase as a component of the SRK signaling pathway and demonstrated ARC1’s requirement in the stigma for self-incompatible pollen rejection in Brassica napus, Arabidopsis lyrata, and Arabidopsis thaliana. Here, we discuss our findings on the role of ARC1 in reconstructing a strong and stable A. thaliana self-incompatibility phenotype, in the context of the putative issues outlined in a commentary by Nasrallah and Nasrallah. Additionally, with their proposed standardized strategy for studying self-incompatibility in A. thaliana, we offer our perspective on what constitutes a strong and stable self-incompatibility phenotype in A. thaliana and how this should be investigated and reported to the greater community.

Reversible ubiquitylation in plant biology

Abstract: Post-translational modification by ubiquitin plays a critical regulatory function in nearly all aspects of plant biology (Vierstra, 2009). Diverse conjugation enzymes attach monoubiquitin or polyubiquitin, with eight different linkages, as distinct signals to the regulatory and mechanistic components of various cellular processes. This ebook updates the functions, targets, and mechanisms of the conjugation components involved in the monoubiquitination of histones H2A and H2B and the polyubiquitination of all linkage types. Additionally, the roles and mechanisms of E3 ligases in biotic and abiotic stress responses and self-incompatibility (SI) and the regulation of cullin-based ligases (CRLs) by neddylation/deneddylation are updated. Finally, the functional roles of deubiquitination enzymes (DUBs) are reviewed together with a report on the biochemical and phylogenetic analyses of Arabidopsis OTU DUBs that support their functional differences.

Signaling Events in Pollen Acceptance or Rejection in the Arabidopsis Species

Abstract: The initial events of pollen–pistil interactions are fundamentally important in flowering plants because they influence 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 field 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 receptor–ligand 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.

Autophagy in the rejection of self-pollen in the mustard family

Abstract: Autophagy is an integral part of the plant life cycle where it contributes to remodeling of tissues during plant development, and in plant responses to nutrient deficiencies, pathogens, and other environmental stresses. Recently, we reported the involvement of autophagy as part of the self-incompatibility response in the mustard family. Self-incompatibility is a polymorphic genetic system that results in rejection of self-incompatible male pollen by the female pistil, thereby preventing self-fertilization. Our data show that autophagy is part of the cellular rejection response in the underlying pistil cells to prevent vesicle secretion to self-pollen thus causing rejection.