Stigmatic Surface Research Articles

Floral Microcharacters in South American species of Senecio s.str. (Asteraceae) with considerations on the circumscription of this genus

Senecio L. s.str. is the largest genus in the tribe Senecioneae (Asteraceae) and it has been commonly characterized by its truncate, penicillate stylar tips, separated stigmatic lines, and stamens usually with ecaudate anther bases and balusterform filament collar. A micromorphological study was carried out to determine if South American species of Senecio s.str. present these diagnostic micromorphological characters, as a contribution towards a circumscription of this genus supported by morphology. The study included 72 South American Senecio species from eight sections and 16 series, as well as species from six other genera of subtribe Senecioninae (Delairea, Dendrophorbium, Dendrosenecio, Graphistylis, Lomanthus, Pentacalia), three genera of subtribe Tussilagininae (Aequatorium, Nordenstamia, Roldana), and one of subtribe Brachyglottidinae (Acrisione). The studied characters include: style branches (stigmatic surface, and apices), anthers (filament collar, bases, and appendages), as well as pollen features (shape, size, and sculpture). Analyses of these characters suggested that Senecio s.str. can be defined only by the presence of balusterform filament collars, which are present in 61 out of the 72 studied Senecio s.str. species (vs. cylindrical collar in remaining species). The genera Graphistylis and Delairea also show this trait, however, Graphistylis presents some microcharacters (e.g. “banded” stigmatic surface) that are rather infrequently found in Senecio s.str. Senecio grandis showed cylindrical collars and sagittate anther bases and should be excluded from the genus. The other microcharacters analyzed appeared to be taxonomically uninformative, since their predominant states were found in Senecio s.str. as well as in other genera of Senecioneae.

Male gametophyte development and function in angiosperms: a general concept.

Overview of pollen development. Male gametophyte development of angiosperms is a complex process that requires coordinated activity of different cell types and tissues of both gametophytic and sporophytic origin and the appropriate specific gene expression. Pollen ontogeny is also an excellent model for the dissection of cellular networks that control cell growth, polarity, cellular differentiation and cell signaling. This article describes two sequential phases of angiosperm pollen ontogenesis-developmental phase leading to the formation of mature pollen grains, and a functional or progamic phase, beginning with the impact of the grains on the stigma surface and ending at double fertilization. Here we present an overview of important cellular processes in pollen development and explosive pollen tube growth stressing the importance of reserves accumulation and mobilization and also the mutual activation of pollen tube and pistil tissues, pollen tube guidance and the communication between male and female gametophytes. We further describe the recent advances in regulatory mechanisms involved such as posttranscriptional regulation (including mass transcript storage) and posttranslational modifications to modulate protein function, intracellular metabolic signaling, ionic gradients such as Ca(2+) and H(+) ions, cell wall synthesis, protein secretion and intercellular signaling within the reproductive tissues.

Significance of stigma receptivity in intergeneric cross-pollination of Salix × Populus

The pollen–stigma interaction plays an important role in reproductive process and has been continuously studied in many interspecific and intergeneric crossing experiments. The aim of this study was to investigate stigma receptivity (SR) of willow in order to determine the most suitable period for its pollination with poplar pollen and improve the effectiveness of <em>Salix × Populus</em> crosses. Tissue samples were examined histologically using light, epifluorescent, scanning, and transmission electron microscopy. Willow SR was determined by stigma morphological traits, test of pollen germination rate, Peroxtesmo test of peroxidase and esterase activity on stigma surface as well as papilla ultrastructure at anthesis. We have ascertained that the SR duration in willow is short, lasting from 1 to 2 DA. The poplar pollen germination rate on willow stigmas on 1 DA ranged from 26.3 to 11.2%.

Pressure sensitive microparticle adhesion through biomimicry of the pollen-stigma interaction.

Many soft biomimetic synthetic adhesives, optimized to support macroscopic masses (∼kg), have been inspired by geckos, insects and other animals. Far less work has investigated bioinspired adhesion that is tuned to micro- and nano-scale sizes and forces. However, such adhesive forces are extremely important in the adhesion of micro- and nanoparticles to surfaces, relevant to a wide range of industrial and biological systems. Pollens, whose adhesion is critical to plant reproduction, are an evolutionary-optimized system for biomimicry to engineer tunable adhesion between particles and micro-patterned soft matter surfaces. In addition, the adhesion of pollen particles is relevant to topics as varied as pollinator ecology, transport of allergens, and atmospheric phenomena. We report the first observation of structurally-derived pressure-sensitive adhesion of a microparticle by using the sunflower pollen and stigma surfaces as a model. This strong, pressure-sensitive adhesion results from interlocking between the pollen's conical spines and the stigma's receptive papillae. Inspired by this behavior, we fabricated synthetic polymeric patterned surfaces that mimic the stigma surface's receptivity to pollen. These soft mimics allow the magnitude of the pressure-sensitive response to be tuned by adjusting the size and spacing of surface features. These results provide an important new insight for soft material adhesion based on bio-inspired principles, namely that ornamented microparticles and micro-patterned surfaces can be designed with complementarity that enable a tunable, pressure-sensitive adhesion on the microparticle size and length scale.

Three new species of Cypella (Iridaceae) from South America, and taxonomic delimitation of C. suffusa Ravenna

Three new species of Cypella are described and illustrated for the complex of grasslands ecosystems of Rio de La Plata: C. aurinegra, C. guttata and C. ravenniana. The former is endemic to the region of the Taquari river, southern Cerro Largo Department, Uruguay, and is closely related to Cypella fucata and C. luteogibbosa, but can be distinguished from these species by its yellow flowers stained with dark-purple, narrower outer tepals, smaller inner tepals, shorter adaxial crests of style branches, slender filaments, and seeds with smooth testa. Cypella guttata occurs in Artigas and Rivera Departments, northern Uruguay, and in Santana do Livramento Municipality, southwestern Rio Grande do Sul State, Brazil. This species resembles C. herbertii and C. lapidosa, and can be distinguished by its flowers with central depression showing red spots, filaments narrower and tape-shaped, style branches with shorter adaxial crests, and small transverse stigmatic surface of the abaxial crest. The range of geographic distribution of C. ravenniana includes southern Misiones, and northeast Corrientes Provinces, Argentina, and west and northwest Rio Grande do Sul State, Brazil. This species can be recognized by its one-flowered spathes, borne on short peduncles. Cypella ravenniana was firstly misidentified as C. suffusa; however, having as base the type and topotypical collections of the latter species, C. suffusa is recognized by its two-flowered spathes borne on long peduncles, and perigone golden-yellow with deep central concavity. Data about phenology, geographic distribution, conservation and dichotomous keys to segregate these three new species from its related species are supplied.

Seasonal changes in pollen limitation and femaleness along the snowmelt gradient in a distylous alpine herb,Primula modesta

Flowering phenology of alpine plants is strongly determined by the timing of snowmelt, and the conditions of pollination of widely distributed plants vary greatly during their flowering season. We examined the reproductive success of the distylous alpine herb, Primula modesta, along the snowmelt gradient under natural conditions, and compared it with the result of artificial pollination experiments. In addition, the compositions and visit frequencies of pollinators to the flower of P. modesta were examined during the flowering period. The pin and thrum plants of P. modesta growing at the same site have an equal ability to produce seeds if a sufficient amount of legitimate pollen grains are deposited on the stigma surface. However, under natural conditions, their seed‐set success was often (even if not always) restricted by pollen limitation, and the functional gender of the pin and thrum plants biased to the female and male, respectively, associated with their growing sites. These variations were not ascribed to resource limitation nor biased morph ratio but to the seasonal changes in pollination situations, a replacement of pollinator types from long‐ to short‐tongued pollinators resulted in unidirectional pollen transfer from long stamens (thrum plants) to long styles (pin plants). The functional gender specialization may enhance the evolution of dioecy from heterostyly, but the severe pollen limitation may cause the breakdown of heterostyly into homostyly. To consider the evolutionary pathway of heterostylous plants, an accumulation of the empirical data is required demonstrating how phenological synchrony between plants and pollinators is decided and to what degree this relationship is stable over years, along with estimates of selection and gene flow in individual plants.

Stigmatic receptivity determines the seed set in Indian mustard, rice and wheat crops

Stigmatic receptivity restricts the successful pollination in cereal crops. The present study deals with the biochemical test for enzymes producing in stigma of field crops such as Indian mustard, rice and wheat. The alcohol dehydrogenase and hydrogen peroxide assays revealed stigmatic receptivity as a violet color and oxygen bubbles released by the chemical reaction. Therefore, the 2 quick tests are in conformity to each other and supported the seed set data, which was utmost at blooming stage of flower ranged between 2–4 d All the 3 crops showed variation in stigmatic receptivity with respect to different time periods of blooming stages and hence, it may affects simultaneous pollen germination and tube growth, fertilization and seed set. The present finding suggests that the growth of pollen tube and stigma receptivity could be influenced by specific enzymes on stigma surface after 2–4 d of blooming stage, which contributes to proper seed set.

Pollination triggers female gametophyte development in immature Nicotiana tabacum flowers

In Nicotiana tabacum, female gametophytes are not fully developed at anthesis, but flower buds pollinated 12 h before anthesis produce mature embryo sacs. We investigated several pollination-associated parameters in N. tabacum flower buds to determine the developmental timing of important events in preparation for successful fertilization. First, we performed hand pollinations in flowers from stages 4 to 11 to study at which developmental stage pollination would produce fruits. A Peroxtesmo test was performed to correlate peroxidase activity on the stigma surface, indicative of stigma receptivity, with fruit set. Pollen tube growth and female gametophyte development were microscopically analyzed in pistils of different developmental stages. Fruits were obtained only after pollinations of flower buds at late stage 7 and older; fruit weight and seed germination capacity increased as the developmental stage of the pollinated flower approached anthesis. Despite positive peroxidase activity and pollen tube growth, pistils at stages 5 and 6 were unable to produce fruits. At late stage 7, female gametophytes were undergoing first mitotic division. After 24 h, female gametophytes of unpollinated pistils were still in the end of the first division, whereas those of pollinated pistils showed egg cells. RT-qPCR assay showed that the expression of the NtEC1 gene, a marker of egg cell development, is considerably higher in pollinated late stage 7 ovaries compared with unpollinated ovaries. To test whether ethylene is the signal eliciting female gametophyte maturation, the expression of ACC synthase was examined in unpollinated and pollinated stage 6 and late stage 7 stigmas/styles. Pollination induced NtACS expression in stage 6 pistils, which are unable to produce fruits. Our results show that pollination is a stimulus capable of triggering female gametophyte development in immature tobacco flowers and suggests the existence of a yet undefined signal sensed by the pistil.

Floral miniaturisation and autogamy in boreal-arctic plants are epitomised by Iceland's most frequent orchid, Platanthera hyperborea.

Background and Aims. This paper concludes our series of publications comparing island and mainland speciation in European butterfly-orchids, by studying the morphology, phylogenetics and reproductive biology of the controversial circum-arctic species Platanthera (Limnorchis) hyperborea—the most frequent of seven Icelandic orchids. We draw particular attention to its phylogenetic placement, remarkable reproductive biology and morphological convergence on other Platanthera lineages through floral miniaturisation.Methods. Five populations of P. hyperborea in southwest Iceland were measured for 33 morphological characters and subjected to detailed multivariate and univariate analyses, supported by light and scanning electron microscopy of selected flowers. Representative samples from six populations were sequenced for nrITS and placed in a taxonomically broader phylogenetic matrix derived from previous studies.Key Results . Section Limnorchis consists of three distinct ITS-delimited clades based on P. stricta, P. sparsifolia–limosa–aquilonis and P. dilatata–hyperborea. Within the latter group, supposed species boundaries overlap; instead, the data indicate a crude stepwise series of ribotypic transitions extending eastward from North America to Iceland. Morphometric data failed to identify any taxonomically meaningful partitions among Icelandic P. hyperborea populations, despite the presence of a distinct and apparently plesiomorphic ribotype at the most glacially influenced habitat sampled. Microscopic study of the flowers revealed several distinguishing features (some not previously reported), including resupinate lateral sepals, toothed bract margins, club-shaped papillae shared by both the interior of the labellar spur and the stigmatic surface, and an exceptionally adhesive stigma that is reliably covered in disaggregated pollen masses prior to anthesis; auricles are absent.Conclusions. Ribotypes suggest that Icelandic P. hyperborea represents the terminus of a migration route that may have begun in East Asia before passing through North America and presumably Greenland. The incohesive pollinia, rapidly desiccating anther locules, weakly developed rostellum, exceptionally adhesive stigma and the close juxtaposition of compact male and female reproductive organs together conspire to cause routine autogamy and frequent cleistogamy, despite the continued production of substantial nectar reservoirs in the spur and consequent ongoing attraction to the flowers of insects, including mosquitoes. When considered in combination with independently derived lineages of Platanthera on the Azorean and Hawaiian archipelagos also bearing small green flowers, our observations show allometric and paedomorphic reductions in flower size as the primary evolutionary driver, but also indicate strong developmental and functional constraints.

Stigma morphological study and numerical taxonomy of genus Pedicularis L. (Orobanchaceae) in Iran

Pedicularis L. (Orobanchaceae) is a large hemiparasitic genus, distributed mostly over boreal and arctic - alpine regions of the northern hemisphere. In the present study 9 species of the genus that are reported in flora of Iran, were undertaken for stigma morphological study and numerical analysis. The stigmatic surface is even in P. pycnantha and P. wilhelmsiana , is expanded into a subspherical shape in P. cabulica , P. caucasica , P. rechingeri , P. sibthorpii , P. condensata and P. strausii and is conical f orm in P. rhinanthoides . To determine the relationship between species, numerical analysis was carried out using 45 quantitative and qualitative morphological, anatomical and palynological characters. UPGMA and PCA dendrograms were drawn. According to the results some characters such as the thickness of pericarp, the thickness of spongy parenchyma, the length of stem, the thickness of bark, the thickness of stem and the length of midrib are the most variable, and can be used for identification and deter mination of relationship between species.

In vivo imaging of the S-locus receptor kinase, the female specificity determinant of self-incompatibility, in transgenic self-incompatible Arabidopsis thaliana.

The S-locus receptor kinase (SRK), which is expressed in stigma epidermal cells, is responsible for the recognition and inhibition of 'self' pollen in the self-incompatibility (SI) response of the Brassicaceae. The allele-specific interaction of SRK with its cognate pollen coat-localized ligand, the S-locus cysteine-rich (SCR) protein, is thought to trigger a signalling cascade within the stigma epidermal cell that leads to the arrest of 'self' pollen at the stigma surface. In addition to the full-length signalling SRK receptor, stigma epidermal cells express two other SRK protein species that lack the kinase domain and whose role in the SI response is not understood: a soluble version of the SRK ectodomain designated eSRK and a membrane-tethered form designated tSRK. The goal of this study was to describe the sub-cellular distribution of the various SRK protein species in stigma epidermal cells as a prelude to visualizing receptor dynamics in response to SCR binding. The Arabidopsis lyrata SRKb variant was tagged with the Citrine variant of yellow fluorescent protein (cYFP) and expressed in A. thaliana plants of the C24 accession, which had been shown to exhibit a robust SI response upon transformation with the SRKb-SCRb gene pair. The transgenes used in this study were designed for differential production and visualization of the three SRK protein species in stigma epidermal cells. Transgenic stigmas were analysed by pollination assays and confocal microscopy. Pollination assays demonstrated that the cYFP-tagged SRK proteins are functional and that the eSRK is not required for SI. Confocal microscopic analysis of cYFP-tagged SRK proteins in live stigma epidermal cells revealed the differential sub-cellular localization of the three SRK protein species but showed no evidence for redistribution of these proteins subsequent to incompatible pollination.

Field Crops and the Fear of Heat Stress – Opportunities, Challenges and Future Directions

The increased probability of occurrence of more intense and frequent heat stress episodes and extended warmer nights in the future are major challenges towards sustaining agricultural production. Cereals, millets and oil seed crops respond differently to increasing temperature at different growth and developmental stages but are highly susceptible to heat stress during the gametogenesis and the flowering stages. Interestingly, the duration of stress exposure induces differential responses i.e. season-long exposure to high-temperature and short episodes of heat stress coinciding with reproductive processes. Season-long high-temperature stress decreased biomass production, seed number, individual seed weight and yield of all grain crops. Short duration heat stress coinciding with either gametogenesis or anthesis leads to negative impact of seed-set, while stress exposure at post-anthesis stages decreased seed filling duration leading to decreased seed weight. Based on extensive research we have identified temperature thresholds across field crops and quantified the above changes. Impact of heat stress on pollen production, pollen viability, pollen lipid profiles, alternations in the pollen and stigmatic surface, pollen reactive oxygen species production, their membrane damage etc., differentiating contrasting cultivars across different field crops will be highlighted. In addition, considering the differential rate of increase in minimum night temperature, different physiological routes inducing yield losses under high day and high night temperature will be presented. Genetic variability across field crops in response to heat stress and more interestingly options from wild species of wheat (higher heat tolerance at flowering), rice (heat escape through early morning flowering) and their usefulness in heat stress tolerance breeding will be an interesting addition to our talk. The current progress achieved, opportunities available, unaddressed challenges and future direction of research that could help in crop improvement to sustain global food production under future hotter climates will be discussed.

The morphology of the stigma surface of Petunia hybrida hort. superbissima as seen in scanning electron microscopy

The ultrastructure of stigma surface in allotetraploid petunias was analyzed by scanning electron microscopy. The stigma forms a bilobed structure with. a distinct central depression. The stigma surface is covered with numerous. papillate hairs of ununiform sizes and shapes.

Transcriptional characteristics and differences in Arabidopsis stigmatic papilla cells pre- and post-pollination.

Pollination is an important early step in sexual plant reproduction. In Arabidopsis thaliana, sequential pollination events, from pollen adhesion onto the stigma surface to pollen tube germination and elongation, occur on the stigmatic papilla cells. Following successful completion of these events, the pollen tube penetrates the stigma and finally fertilizes a female gametophyte. The pollination events are thought to be initiated and regulated by interactions between papilla cells and pollen. Here, we report the characterization of gene expression profiles of unpollinated (UP), compatible pollinated (CP) and incompatible pollinated (IP) papilla cells in A. thaliana. Based on cell type-specific transcriptome analysis from a combination of laser microdissection and RNA sequencing, 15,475, 17,360 and 16,918 genes were identified as expressed in UP, CP and IP papilla cells, respectively, and, of these, 14,392 genes were present in all three data sets. Differentially expressed gene (DEG) analyses identified 147 and 71 genes up-regulated in CP and IP papilla cells, respectively, and 115 and 46 genes down-regulated. Gene Ontology and metabolic pathway analyses revealed that papilla cells play an active role as the female reproductive component in pollination, particularly in information exchange, signal transduction, internal physiological changes and external morphological modification. This study provides fundamental information on the molecular mechanisms involved in pollination in papilla cells, furthering our understanding of the reproductive role of papilla cells.

A new species of the Genus Delphinium (Ranunculaceae) from Lahul Valley of Himachal Pradesh, India

A new species of Delphinium (Ranunculaceace) is described and illustrated from Lahul valley of Himachal Pradesh, India. Its affinities with the allied species D. viscosum and D. cashmerianum are discussed. It differs from closely allied species in having bracteoles with hooked apex, shape of spur that resembles parrot’s beak, staminode with dense hoard of hairs at ventral apex, hairs in single line on the inner surface of ovary and cleft stigma.

Orchid mating: the anther steps onto the stigma

In a bisexual flower, the male and female organ of which have a space separation, individing into the pistil and stamen. Due to the spatial separation between male and female pollen grains from the anther of most flowering plants, including orchids, pollens are transported by wind or animals and deposited onto the receptive surface of the stigma of a different plant. Based on observations on floral morphology and flowering phenology, tests of the breeding system, and a comparison of pollination mechanisms, a new pollination process was discovered in the hermaphroditic (i.e., possessing spatially separated male and female organs) flower of a slipper orchid, Paphiopedilum parishii. The anther changes from a solid to a liquid state and directly steps onto the stigma surface without the aid of any pollinating agent or floral assembly. The mode of pollination in Paphiopedilum parishii is a new addition to the broad range of genetic and morphological mechanisms that have evolved in flowering plants to ensure their reproductive success. The present pollination mechanism is a possible adaptation to the insect-scarce habitat of the orchid.

Tapetum specific expression of unedited nad3 gene from safflower and targeting the protein into mitochondria induces male sterility in transgenic tobacco plants

The ability of NAD3 (subunit 3 of the NADH ubiquinone oxidoreductase) encoded by unedited nad3 (u-nad3) gene, when targeted into mitochondria, to cause ablation of tapetum was investigated. A gene construct was developed by cloning the coxIV presequence from yeast and the u-nad3 from safflower under the tapetum specific TA29 promoter to target U-NAD3 into mitochondria in the tapetal cell layer. Transgenic tobacco plants were realized with this construct using the Agrobacterium mediated transformation method and confirmed for the presence of the transgene. Among these plants, three were completely sterile and four were semi-sterile. The male sterile plants were morphologically similar to fertile plants, but the anthers were shorter and remained regressed below the stigma surface at anthesis. RT-PCR and western blotting confirmed anther specific expression of u-nad3 in these plants. Stable inheritance of the induced male sterility and its co-segregation with the introduced gene cassette was confirmed in the test cross progeny. This study demonstrates the proof-of-concept that u-nad3 could be used as a candidate to induce transgenic male sterility in plants.

INCOMPATIBILITY ALLELES OF HAZELNUT CULTIVARS

Pollen-stigma incompatibility in hazelnut is sporophytic and under the control of a single locus with multiple alleles. To date, 33 alleles have been identified at the S-locus, and a designated pollen tester for each preserved in our collection. Hazelnut is diploid, and nearly all cultivars are heterozygous at the S-locus. Over the past 25 years, we have enlarged our collection by importing cultivars from several countries as scions. As the trees began to flower, we identified their S-alleles using florescence microscopy. In December, we bagged emasculated branches on trees growing in the field to protect the female inflorescences from wind-borne pollen. In January, we collected pollen from our tester trees. In February, females were collected from bagged branches and brought to the lab in petri dishes. The females were pollinated in the afternoon, one or two per tester pollen. The following day, the styles were squashed in aniline blue and observed under UV light. In compatible pollinations, pollen germination was excellent and tubes could be seen growing parallel down the style. In incompatible pollinations, germination was often reduced, pollen tubes were short and did not penetrate the stigmatic surface, and the tubes often ended in bulbs. Each pollination was scored as compatible or incompatible, and the testing of a tree required 1-3 years for completion. In this paper, we report the alleles of 170 cultivars for the first time, and summarize the alleles of 112 cultivars previously typed. Cultivars with different names often have identical microsatellite marker fingerprints and S-alleles. To reduce confusion, a list of cultivars with identical fingerprints is also included.

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

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.

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.