An ATP-binding cassette transporter, OsABCB24, is involved in female gametophyte development and early seed growth in rice.

Female gametogenesis has been rarely studied due to gametophyte lethality and the unavailability of related genetic resources. In this study, we identified a rice ATP-binding cassette transporter, OsABCB24, whose null function displayed a significantly reduced seed setting rate by as much as 94%-100% compared with that of the wild type (WT). The reciprocal cross of WT and mutant plants demonstrated that the female reproductive organs in mutants were functionally impaired. Confocal microscopy observations revealed that, although megasporogenesis remained unaffected in CRISPR/Cas9 osabcb24 mutants, the formation of female gametophytes was interrupted. Additionally, the structure of the syncytial nucleus was impaired during the initial stages of endosperm formation. Histochemical analysis showed that OsABCB24 was preferentially expressed at the conjunction of receptacle and ovary, spanning from the functional megaspore stage to the two-nucleate embryo sac stage. Further, OsABCB24 was identified as an endoplasmic reticulum membrane-localized protein. Notably, the overexpression of OsABCB24 triggered a 1.5- to 2-fold increase in grain production compared to the WT. Our findings showed that OsABCB24 plays a key role in both female gametophyte development and the early development of seeds.

Life table parameters of Amblyseius largoensis, Amblyseius swirskii and Proprioseiopsis lenis (Acari: Phytoseiidae) fed on eggs and larvae of Frankliniella occidentalis.

The immature development and reproduction of the predatory mites Amblyseius largoensis (Muma), Proprioseiopsis lenis (Corpuz and Rimando), and Amblyseius swirskii Athias-Henriot (Acari: Phytoseiidae) were investigated using both thrips eggs and first instars of the western flower thrips, Frankliniella occidentalis Pergande, as prey in a controlled laboratory environment at 25 °C and 60% relative humidity. When provided with thrips eggs as food, A. largoensis exhibited a notably shorter immature development period for both males (7.05 days) and females (6.51 days) as compared with A. swirskii (8.05 and 7.19 days, respectively) and P. lenis (8.10 days and 7.05 days, respectively). Amblyseius largoensis also displayed a higher oviposition rate (2.19 eggs/female/day) than A. swirskii and P. lenis (1.79 and 1.78 eggs/female/day, respectively). Moreover, it exhibited the highest fecundity (25.34 eggs/female), followed by P. lenis (24.23 eggs/female) and A. swirskii (22.86 eggs/female). These variations led to A. largoensis having the highest intrinsic rate of increase (rm) at 0.209, followed by A. swirskii at 0.188, and P. lenis at 0.165. However, when the predatory mites were provided with first instars of F. occidentalis, A. swirskii demonstrated a faster immature development period for both males (7.67 days) and females (7.59 days) as compared with P. lenis (9.00 days and 7.86 days, respectively) and A. largoensis (8.47 days and 8.61 days, respectively). While the oviposition rates of P. lenis (1.92 eggs/female/day) and A. swirskii (1.90 eggs/female/day) were similar when feeding on this prey, A. largoensis produced fewer eggs (1.83 eggs/female/day). Further, A. swirskii exhibited the highest fecundity (31.93 eggs/female), followed by A. largoensis (25.71 eggs/female) and P. lenis (23 eggs/female). Consequently, the intrinsic rate of increase (rm) on thrips first instars was highest in A. swirskii (0.190), followed by A. largoensis (0.186), and P. lenis (0.176). In summary, our findings indicate that in terms of life history parameters A. largoensis performs optimally when feeding on thrips eggs, whereas A. swirskii performs best when preying on the mobile first instars of the thrips. These insights into the dietary preferences and reproductive capabilities of the studied predatory mite species have important implications for their potential use as biological control agents against F. occidentalis in agricultural settings.

Topological analysis of 3D digital ovules identifies cellular patterns associated with ovule shape diversity.

Tissue morphogenesis remains poorly understood. In plants, a central problem is how the 3D cellular architecture of a developing organ contributes to its final shape. We address this question through a comparative analysis of ovule morphogenesis, taking advantage of the diversity in ovule shape across angiosperms. Here, we provide a 3D digital atlas of Cardamine hirsuta ovule development at single cell resolution and compare it with an equivalent atlas of Arabidopsis thaliana. We introduce nerve-based topological analysis as a tool for unbiased detection of differences in cellular architectures and corroborate identified topological differences between two homologous tissues by comparative morphometrics and visual inspection. We find that differences in topology, cell volume variation and tissue growth patterns in the sheet-like integuments and the bulbous chalaza are associated with differences in ovule curvature. In contrast, the radialized conical ovule primordia and nucelli exhibit similar shapes, despite differences in internal cellular topology and tissue growth patterns. Our results support the notion that the structural organization of a tissue is associated with its susceptibility to shape changes during evolutionary shifts in 3D cellular architecture.

Genome-Wide Characterization and Functional Validation of the ACS Gene Family in the Chestnut Reveals Its Regulatory Role in Ovule Development.

Ovule abortion significantly contributes to a reduction in chestnut yield. Therefore, an examination of the mechanisms underlying ovule abortion is crucial for increasing chestnut yield. In our previous study, we conducted a comprehensive multiomic analysis of fertile and abortive ovules and found that ACS genes in chestnuts (CmACS) play a crucial role in ovule development. Therefore, to further study the function of ACS genes, a total of seven CmACS members were identified, their gene structures, conserved structural domains, evolutionary trees, chromosomal localization, and promoter cis-acting elements were analyzed, and their subcellular localization was predicted and verified. The spatiotemporal specificity of the expression of the seven CmACS genes was confirmed via qRT-PCR analysis. Notably, CmACS7 was exclusively expressed in the floral organs, and its expression peaked during fertilization and decreased after fertilization. The ACC levels remained consistently greater in fertile ovules than in abortive ovules. The ACSase activity of CmACS7 was identified using the genetic transformation of chestnut healing tissue. Micro Solanum lycopersicum plants overexpressing CmACS7 had a significantly greater rate of seed failure than did wild-type plants. Our results suggest that ovule fertilization activates CmACS7 and increases ACC levels, whereas an overexpression of CmACS7 leads to an increase in ACC content in the ovule prior to fertilization, which can lead to abortion. In conclusion, the present study demonstrated that chestnut ovule abortion is caused by poor fertilization and not by nutritional competition. Optimization of the pollination and fertilization of female flowers is essential for increasing chestnut yield and reducing ovule abortion.

SlCRCa is a key D-class gene controlling ovule fate determination in tomato.

Cell fate determination and primordium initiation on the placental surface are two key events for ovule formation in seed plants, which directly affect ovule density and seed yield. Despite ovules form in the marginal meristematic tissues of the carpels, angiosperm carpels evolved after the ovules. It is not clear how the development of the ovules and carpels is coordinated in angiosperms. In this study, we identify the S. lycopersicum CRABS CLAW (CRC) homologue SlCRCa as an essential determinant of ovule fate. We find that SlCRCa is not only expressed in the placental surface and ovule primordia but also functions as a D-class gene to block carpel fate and promote ovule fate in the placental surface. Loss of function of SlCRCa causes homeotic transformation of the ovules to carpels. In addition, we find low levels of the S. lycopersicum AINTEGUMENTA (ANT) homologue (SlANT2) favour the ovule initiation, whereas high levels of SlANT2 promote placental carpelization. SlCRCa forms heterodimer with tomato INNER NO OUTER (INO) and AGAMOUS (AG) orthologues, SlINO and TOMATO AGAMOUS1 (TAG1), to repress SlANT2 expression during the ovule initiation. Our study confirms that angiosperm basal ovule cells indeed retain certain carpel properties and provides mechanistic insights into the ovule initiation.

Development of pollinated and unpollinated ovules in Ginkgo biloba: unravelling the role of pollen in ovule tissue maturation.

In gymnosperms such as Ginkgo biloba, the arrival of pollen plays a key role in ovule development, before fertilization occurs. Accordingly, G. biloba female plants geographically isolated from male plants abort all their ovules after the pollination drop emission, which is the event that allows the ovule to capture pollen grains. To decipher the mechanism induced by pollination required to avoid ovule senescence and then abortion, we compared the transcriptomes of pollinated and unpollinated ovules at three time points after the end of the emission of pollination drop. Transcriptomic and in situ expression analyses revealed that several key genes involved in programmed cell death such as senescence and apoptosis, DNA replication, and cell cycle regulation were differentially expressed in unpollinated ovules compared to pollinated ovules. We provide evidence that the pollen captured by the pollination drop affects auxin local accumulation and might cause deregulation of key genes required for the ovule's programmed cell death, activating both the cell cycle regulation and DNA replication genes.

Maternal nitric oxide homeostasis impacts female gametophyte development under optimal and stress conditions.

In adverse environments, the number of fertilizable female gametophytes (FGs) in plants is reduced, leading to increased survival of the remaining offspring. How the maternal plant perceives internal growth cues and external stress conditions to alter FG development remains largely unknown. We report that homeostasis of the stress signaling molecule nitric oxide (NO) plays a key role in controlling FG development under both optimal and stress conditions. NO homeostasis is precisely regulated by S-nitrosoglutathione reductase (GSNOR). Prior to fertilization, GSNOR protein is exclusively accumulated in sporophytic tissues and indirectly controls FG development in Arabidopsis (Arabidopsis thaliana). In GSNOR null mutants, NO species accumulated in the degenerating sporophytic nucellus, and auxin efflux into the developing FG was restricted, which inhibited FG development, resulting in reduced fertility. Importantly, restoring GSNOR expression in maternal, but not gametophytic tissues, or increasing auxin efflux substrate significantly increased the proportion of normal FGs and fertility. Furthermore, GSNOR overexpression or added auxin efflux substrate increased fertility under drought and salt stress. These data indicate that NO homeostasis is critical to normal auxin transport and maternal control of FG development, which in turn determine seed yield. Understanding this aspect of fertility control could contribute to mediating yield loss under adverse conditions.

Interspecific complementation-restoration of phenotype in Arabidopsis cuc2cuc3 mutant by sugarcane CUC2 gene.

BACKGROUND: In plants, a critical balance between differentiation and proliferation of stem cells at the shoot apical meristem zone is essential for proper growth. The spatiotemporal regulation of some crucial genes dictates the formation of a boundary within and around budding organs. The boundary plays a pivotal role in distinguishing one tissue type from another and provides a defined shape to the organs at their developed stage. NAM/CUC subfamily of the NAC transcription factors control the boundary formation during meristematic development. RESULTS: Here, we have identified the CUP-SHAPED COTYLEDON (CUC) genes in sugarcane and named SsCUC2 (for the orthologous gene of CUC1 and CUC2) and SsCUC3. The phylogenetic reconstruction showed that SsCUCs occupy the CUC2 and CUC3 clade together with monocots, whereas eudicot CUC2 and CUC3 settled separately in the different clade. The structural analysis of CUC genes showed that most of the CUC3 genes were accompanied by an intron gain during eudicot divergence. Besides, the study of SsCUCs expression in the RNA-seq obtained during different stages of ovule development revealed that SsCUCs express in developing young tissues, and the expression of SsCUC2 is regulated by miR164. We also demonstrate that SsCUC2 (a monocot) could complement the cuc2cuc3 mutant phenotype of Arabidopsis (eudicot). CONCLUSIONS: This study further supports that CUC2 has diverged in CUC1 and CUC2 during the evolution of monocots and eudicots from ancestral plants. The functional analysis of CUC expression patterns during sugarcane ovule development and ectopic expression of SsCUC2 in Arabidopsis showed that SsCUC2 has a conserved role in boundary formation. Overall, these findings improve our understanding of the functions of sugarcane CUC genes. Our results reveal the crucial functional role of CUC genes in sugarcane.

Flower meristem maintenance by TILLERS ABSENT 1 is essential for ovule development in rice.

Plant development depends on the activity of pluripotent stem cells in meristems, such as the shoot apical meristem and the flower meristem. In Arabidopsis thaliana, WUSCHEL (WUS) is essential for stem cell homeostasis in meristems and integument differentiation in ovule development. In rice (Oryza sativa), the WUS ortholog TILLERS ABSENT 1 (TAB1) promotes stem cell fate in axillary meristem development, but its function is unrelated to shoot apical meristem maintenance in vegetative development. In this study, we examined the role of TAB1 in flower development. The ovule, which originates directly from the flower meristem, failed to differentiate in tab1 mutants, suggesting that TAB1 is required for ovule formation. Expression of a stem cell marker was completely absent in the flower meristem at the ovule initiation stage, indicating that TAB1 is essential for stem cell maintenance in the 'final' flower meristem. The ovule defect in tab1 was partially rescued by floral organ number 2 mutation, which causes overproliferation of stem cells. Collectively, it is likely that TAB1 promotes ovule formation by maintaining stem cells at a later stage of flower development.

Effect of Low Temperature on Changes in AGP Distribution during Development of Bellis perennis Ovules and Anthers.

Arabinogalactan proteins (AGPs) are a class of heavily glycosylated proteins occurring as a structural element of the cell wall-plasma membrane continuum. The features of AGPs described earlier suggest that the proteins may be implicated in plant adaptation to stress conditions in important developmental phases during the plant reproduction process. In this paper, the microscopic and immunocytochemical studies conducted using specific antibodies (JIM13, JIM15, MAC207) recognizing the carbohydrate chains of AGPs showed significant changes in the AGP distribution in female and male reproductive structures during the first stages of Bellis perennis development. In typical conditions, AGPs are characterized by a specific persistent spatio-temporal pattern of distribution. AGP epitopes are visible in the cell walls of somatic cells and in the megasporocyte walls, megaspores, and embryo sac at every stage of formation. During development in stress conditions, the AGP localization is altered, and AGPs entirely disappear in the embryo sac wall. In the case of male development, AGPs are present in the tapetum, microsporocytes, and microspores in normal conditions. In response to development at lower temperature, AGPs are localized in the common wall of microspores and in mature pollen grains. Additionally, they are accumulated in remnants of tapetum cells.

Differential gene expression patterns during gametophyte development provide insights into sex differentiation in the dioicous kelp Saccharina japonica.

BACKGROUND: In brown algae, dioicy is the prevalent sexual system, and phenotypic differences between male and female gametophytes have been found in many dioicous species. Saccharina japonica show remarkable sexual dimorphism in gametophytes before gametogenesis. A higher level of phenotypic differentiation was also found in female and male gametes after gametogenesis. However, the patterns of differential gene expression throughout gametophyte development and how these changes might relate to sex-specific fitness at the gamete stage in S. japonica are not well known. RESULTS: In this study, differences in gene expression between male and female gametophytes in different developmental stages were investigated using comparative transcriptome analysis. Among the 20,151 genes expressed in the haploid gametophyte generation, 37.53% were sex-biased. The abundance of sex-biased genes in mature gametophytes was much higher than that in immature gametophytes, and more male-biased than female-biased genes were observed in the mature stage. The predicted functions of most sex-biased genes were closely related to the sex-specific characteristics of gametes, including cell wall biosynthesis, sperm motility, and sperm and egg recognition. In addition, 51 genes were specifically expressed in males in both stages, showing great potential as candidate male sex-determining region (SDR) genes. CONCLUSIONS: This study describes a thorough investigation into differential gene expression between male and female gametophytes in the dioicous kelp S. japonica. A large number of sex-biased genes in mature gametophytes may be associated with the divergence of phenotypic traits and physiological functions between female gametes (eggs) and male gametes (sperm) during sexual differentiation. These genes may mainly come from new sex-biased genes that have recently evolved in the S. japonica lineage. The duplication of sex-biased genes was detected, which may increase the number of sex-biased genes after gametogenesis in S. japonica to some extent. The excess of male-biased genes over female-biased genes in the mature stage may reflect the different levels of sexual selection across sexes. This study deepens our understanding of the regulation of sex development and differentiation in the dioicous kelp S. japonica.

MircroRNA Profiles of Early Rice Inflorescence Revealed a Specific miRNA5506 Regulating Development of Floral Organs and Female Megagametophyte in Rice.

The developmental process of inflorescence and gametophytes is vital for sexual reproduction in rice. Multiple genes and conserved miRNAs have been characterized to regulate the process. The changes of miRNAs expression during the early development of rice inflorescence remain unknown. In this study, the analysis of miRNAs profiles in the early stage of rice inflorescence development identified 671 miRNAs, including 67 known and 44 novel differentially expressed miRNAs (DEMs). Six distinct clusters of miRNAs expression patterns were detected, and Cluster 5 comprised 110 DEMs, including unconserved, rice-specific osa-miR5506. Overexpression of osa-miR5506 caused pleiotropic abnormalities, including over- or under-developed palea, various numbers of floral organs and spikelet indeterminacy. In addition, the defects of ovaries development were frequently characterized by multiple megasporocytes, ovule-free ovary, megasporocyte degenerated and embryo sac degenerated in the transgenic lines. osa-miR5506 targeted REM transcription factor LOC_Os03g11370. Summarily, these results demonstrated that rice-specific osa-miR5506 plays an essential role in the regulation of floral organ number, spikelet determinacy and female gametophyte development in rice.

Deciphering the evolution of the ovule genetic network through expression analyses in Gnetum gnemon.

BACKGROUND AND AIMS: The ovule is a synapomorphy of all seed plants (gymnosperms and angiosperms); however, there are some striking differences in ovules among the major seed plant lineages, such as the number of integuments or the orientation of the ovule. The genetics involved in ovule development have been well studied in the model species Arabidopsis thaliana, which has two integuments and anatropous orientation. This study is approached from what is known in arabidopsis, focusing on the expression patterns of homologues of four genes known to be key for the proper development of the integuments in arabidopsis: AINTEGUMENTA (ANT), BELL1, (BEL1), KANADIs (KANs) and UNICORN (UCN). METHODS: We used histology to describe the morphoanatomical development from ovules to seeds in Gnetum gnemon. We carried out spatiotemporal expression analyses in G. gnemon, a gymnosperm, which has a unique ovule morphology with an integument covering the nucellus, two additional envelopes where the outermost becomes fleshy as the seed matures, and an orthotropous orientation. KEY RESULTS: Our anatomical and developmental descriptions provide a framework for expression analyses in the ovule of G. gnemon. Our expression results show that although ANT, KAN and UCN homologues are expressed in the inner integument, their spatiotemporal patterns differ from those found in angiosperms. Furthermore, all homologues studied here are expressed in the nucellus, revealing major differences in seed plants. Finally, no expression of the studied homologues was detected in the outer envelopes. CONCLUSIONS: Altogether, these analyses provide significant comparative data that allows us to better understand the functional evolution of these gene lineages, providing a compelling framework for evolutionary and developmental studies of seeds. Our findings suggest that these genes were most likely recruited from the sporangium development network and became restricted to the integuments of angiosperm ovules.

Phosphorylation of WRKY16 by MPK3-1 is essential for its transcriptional activity during fiber initiation and elongation in cotton (Gossypium hirsutum).

Cotton, one of the most important crops in the world, produces natural fiber materials for the textile industry. WRKY transcription factors play important roles in plant development and stress responses. However, little is known about whether and how WRKY transcription factors regulate fiber development of cotton so far. In this study, we show that a fiber-preferential WRKY transcription factor, GhWRKY16, positively regulates fiber initiation and elongation. GhWRKY16-silenced transgenic cotton displayed a remarkably reduced number of fiber protrusions on the ovule and shorter fibers compared to the wild-type. During early fiber development, GhWRKY16 directly binds to the promoters of GhHOX3, GhMYB109, GhCesA6D-D11, and GhMYB25 to induce their expression, thereby promoting fiber initiation and elongation. Moreover, GhWRKY16 is phosphorylated by the mitogen-activated protein kinase GhMPK3-1 at residues T-130 and S-260. Phosphorylated GhWRKY16 directly activates the transcription of GhMYB25, GhHOX3, GhMYB109, and GhCesA6D-D11 for early fiber development. Thus, our data demonstrate that GhWRKY16 plays a crucial role in fiber initiation and elongation, and that GhWRKY16 phosphorylation by GhMPK3-1 is essential for the transcriptional activation on downstream genes during the fiber development of cotton.

Sphingosine Promotes Embryo Biomass in Upland Cotton: A Biochemical and Transcriptomic Analysis.

Sphingolipids are essential membrane components and signal molecules, but their regulatory role in cotton embryo growth is largely unclear. In this study, we evaluated the effects of treatment with the sphingolipid synthesis inhibitor fumonisin B1 (FB1), the serine palmityl transferase (SPT) inhibitor myriocin, the SPT sphingolipid product DHS (d18:0 dihydrosphingosine), and the post-hydroxylation DHS product PHS (t18:0 phytosphingosine) on embryo growth in culture, and performed comparative transcriptomic analysis on control and PHS-treated samples. We found that FB1 could inhibit cotton embryo development. At the five-day ovule/embryo developmental stage, PHS was the most abundant sphingolipid. An SPT enzyme inhibitor reduced the fresh weight of embryos, while PHS had the opposite effect. The transcriptomic analysis identified 2769 differentially expressed genes (1983 upregulated and 786 downregulated) in the PHS samples. A large number of transcription factors were highly upregulated, such as zinc finger, MYB, NAC, bHLH, WRKY, MADS, and GRF in PHS-treated samples compared to controls. The lipid metabolism and plant hormone (auxin, brassinosteroid, and zeatin) related genes were also altered. Our findings provide target metabolites and genes for cotton seed improvement.

MADS-Box Protein Complex VvAG2, VvSEP3 and VvAGL11 Regulates the Formation of Ovules in Vitis vinifera L. cv. 'Xiangfei'.

The phenomenon of multi-carpel and multi-ovule exists in the grapevine cultivar 'Xiangfei', but the mechanism of ovule formation is seldom reported. In this study, we observed the ovule formation process by using 'Xiangfei' grapes. The role of the VvAG2 (VvAGAMOUS) gene in ovule formation was identified, and we explored the relationship between VvAG2, VvSEP3(VvMADS4) and VvAGL11(VvMADS5) proteins. The results showed that the ovule primordium appeared when the inflorescence length of 'Xiangfei' grapes were 4-5 cm long; the relative expression levels of VvAG2, VvAGL11 and VvSEP3 genes were higher during ovule formation, and the expression levels of VvAG2 gene was the highest. Transgenic tomato (Solanum lycopersicum) plants expressing VvAG2 produced higher numbers of ovules and carpels than the wild type. Moreover, yeast two-hybrid and yeast three-hybrid experiments demonstrated that VvSEP3 acts as a bridge and interacts with VvAG2 and VvAGL11 proteins, respectively. Meanwhile, a homodimer can be formed between VvSEP3 and VvSEP3, but there was no interaction between VvAG2 and VvAGL11. These findings suggest that the VvAG2 gene is involved in the formation of ovules, and VvAG2/VvSEP3 together with VvAGL11/VvSEP3 can form a tetrameric complex. In summary, our data showed that VvAG2 along with VvSEP3 and VvAGL11 jointly regulate the ovule formation of 'Xiangfei' grapes.

Dynamics of the cell fate specifications during female gametophyte development in Arabidopsis.

The female gametophytes of angiosperms contain cells with distinct functions, such as those that enable reproduction via pollen tube attraction and fertilization. Although the female gametophyte undergoes unique developmental processes, such as several rounds of nuclear division without cell plate formation and final cellularization, it remains unknown when and how the cell fate is determined during development. Here, we visualized the living dynamics of female gametophyte development and performed transcriptome analysis of individual cell types to assess the cell fate specifications in Arabidopsis thaliana. We recorded time lapses of the nuclear dynamics and cell plate formation from the 1-nucleate stage to the 7-cell stage after cellularization using an in vitro ovule culture system. The movies showed that the nuclear division occurred along the micropylar-chalazal (distal-proximal) axis. During cellularization, the polar nuclei migrated while associating with the forming edge of the cell plate, and then, migrated toward each other to fuse linearly. We also tracked the gene expression dynamics and identified that the expression of MYB98pro::GFP-MYB98, a synergid-specific marker, was initiated just after cellularization in the synergid, egg, and central cells and was then restricted to the synergid cells. This indicated that cell fates are determined immediately after cellularization. Transcriptome analysis of the female gametophyte cells of the wild-type and myb98 mutant revealed that the myb98 synergid cells had egg cell-like gene expression profiles. Although in myb98, egg cell-specific gene expression was properly initiated in the egg cells only after cellularization, but subsequently expressed ectopically in one of the 2 synergid cells. These results, together with the various initiation timings of the egg cell-specific genes, suggest complex regulation of the individual gametophyte cells, such as cellularization-triggered fate initiation, MYB98-dependent fate maintenance, cell morphogenesis, and organelle positioning. Our system of live-cell imaging and cell type-specific gene expression analysis provides insights into the dynamics and mechanisms of cell fate specifications in the development of female gametophytes in plants.

AtLURE1/PRK6-mediated signaling promotes conspecific micropylar pollen tube guidance.

Reproductive isolation is a prerequisite to form and maintain a new species. Multiple prezygotic and postzygotic reproductive isolation barriers have been reported in plants. In the model plant, Arabidopsis thaliana conspecific pollen tube precedence controlled by AtLURE1/PRK6-mediated signaling has been recently reported as a major prezygotic reproductive isolation barrier. By accelerating emergence of own pollen tubes from the transmitting tract, A. thaliana ovules promote self-fertilization and thus prevent fertilization by a different species. Taking advantage of a septuple atlure1null mutant, we now report on the role of AtLURE1/PRK6-mediated signaling for micropylar pollen tube guidance. Compared with wild-type (WT) ovules, atlure1null ovules displayed remarkably reduced micropylar pollen tube attraction efficiencies in modified semi-in vivo A. thaliana ovule targeting assays. However, when prk6 mutant pollen tubes were applied, atlure1null ovules showed micropylar attraction efficiencies comparable to that of WT ovules. These findings indicate that AtLURE1/PRK6-mediated signaling regulates micropylar pollen tube attraction in addition to promoting emergence of own pollen tubes from the transmitting tract. Moreover, semi-in vivo ovule targeting competition assays with the same amount of pollen grains from both A. thaliana and Arabidopsis lyrata showed that A. thaliana WT and xiuqiu mutant ovules are mainly targeted by own pollen tubes and that atlure1null mutant ovules are also entered to a large extent by A. lyrata pollen tubes. Taken together, we report that AtLURE1/PRK6-mediated signaling promotes conspecific micropylar pollen tube attraction representing an additional prezygotic isolation barrier.

Spatiotemporal control of miR398 biogenesis, via chromatin remodeling and kinase signaling, ensures proper ovule development.

The coordinated development of sporophytic and gametophytic tissues is essential for proper ovule patterning and fertility. However, the mechanisms regulating their integrated development remain poorly understood. Here, we report that the Swi2/Snf2-Related1 (SWR1) chromatin-remodeling complex acts with the ERECTA receptor kinase-signaling pathway to control female gametophyte and integument growth in Arabidopsis thaliana by inhibiting transcription of the microRNA gene MIR398c in early-stage megagametogenesis. Moreover, pri-miR398c is transcribed in the female gametophyte but is then translocated to and processed in the ovule sporophytic tissues. Together, SWR1 and ERECTA also activate ARGONAUTE10 (AGO10) expression in the chalaza; AGO10 sequesters miR398, thereby ensuring the expression of three AGAMOUS-LIKE (AGL) genes (AGL51, AGL52, and AGL78) in the female gametophyte. In the context of sexual organ morphogenesis, these findings suggest that the spatiotemporal control of miRNA biogenesis, resulting from coordination between chromatin remodeling and cell signaling, is essential for proper ovule development in Arabidopsis.

A digital 3D reference atlas reveals cellular growth patterns shaping the Arabidopsis ovule.

A fundamental question in biology is how morphogenesis integrates the multitude of processes that act at different scales, ranging from the molecular control of gene expression to cellular coordination in a tissue. Using machine-learning-based digital image analysis, we generated a three-dimensional atlas of ovule development in Arabidopsis thaliana, enabling the quantitative spatio-temporal analysis of cellular and gene expression patterns with cell and tissue resolution. We discovered novel morphological manifestations of ovule polarity, a new mode of cell layer formation, and previously unrecognized subepidermal cell populations that initiate ovule curvature. The data suggest an irregular cellular build-up of WUSCHEL expression in the primordium and new functions for INNER NO OUTER in restricting nucellar cell proliferation and the organization of the interior chalaza. Our work demonstrates the analytical power of a three-dimensional digital representation when studying the morphogenesis of an organ of complex architecture that eventually consists of 1900 cells.