SEUSS and AINTEGUMENTA mediate patterning and ovule initiation during gynoecium medial domain development

The Arabidopsis (Arabidopsis thaliana) gynoecium, the female floral reproductive structure, requires the action of genes that specify positional identities during its development to generate an organ competent for seed development and dispersal. Early in gynoecial development, patterning events divide the primordium into distinct domains that will give rise to specific tissues and organs. The medial domain of the gynoecium gives rise to the ovules, and several other structures critical for reproductive competence. Here we report a synergistic genetic interaction between seuss and aintegumenta mutants resulting in a complete loss of ovule initiation and a reduction of the structures derived from the medial domain. We show that patterning events are disrupted early in the development of the seuss aintegumenta gynoecia and we identify PHABULOSA (PHB), REVOLUTA, and CRABS CLAW (CRC) as potential downstream targets of SEUSS (SEU) and AINTEGUMENTA (ANT) regulation. Our genetic data suggest that SEU additionally functions in pathways that are partially redundant and parallel to PHB, CRC, and ANT. Thus, SEU and ANT are part of a complex and robust molecular system that coordinates patterning cues and cellular proliferation along the three positional axes of the developing gynoecium.     

嘉庚蛸雌性生殖系统组织学观察

对象山港自然海区中的嘉庚蛸(Octopus tankahkeei)雌性生殖系统的组织学结构进行了研究.结果表明,雌性生殖系统由卵巢、输卵管、输卵管腺组成.卵巢单个、球形,内包裹滤泡细胞围成的卵子,输卵管1对,开口于外套腔中部,每条输卵管中部膨大形成圆球状的输卵管腺.近端输卵管内具两瓣蘑菇状突起,上有不规则短指状分枝,突...     

Glorund interactions in the regulation of gurken and oskar mRNAs

Precise temporal and spatial regulation of gene expression during Drosophila oogenesis is essential for patterning the anterior-posterior and dorsal-ventral body axes. Establishment of the anterior-posterior axis requires posterior localization and translational control of both oskar and nanos mRNAs. Establishment of the dorsal-ventral axis depends on the precise restriction of gurken mRNA and protein to the dorsal-anterior corner of the oocyte. We have previously shown that Glorund, the Drosophila hnRNP F/H homolog, contributes to anterior-posterior axis patterning by regulating translation of nanos mRNA, through a direct interaction with its 3′ untranslated region. To investigate the pleiotropy of the glorund mutant phenotype, which includes dorsal-ventral and nuclear morphology defects, we searched for proteins that interact with Glorund. Here we show that Glorund is part of a complex containing the hnRNP protein Hrp48 and the splicing factor Half-pint and plays a role both in mRNA localization and nurse cell chromosome organization, probably by regulating alternative splicing of ovarian tumor. We propose that Glorund is a component of multiple protein complexes and functions both as a translational repressor and splicing regulator for anterior-posterior and dorsal-ventral patterning.     

A new role for the SHATTERPROOF genes during Arabidopsis gynoecium development

Gynoecium development is a complex process which is regulated by key factors that control the spatial formation of the apical, medial and basal parts. SHATTERPROOF1 (SHP1) and SHP2, two closely related MADS-box genes, redundantly control the differentiation of the dehiscence zone and promote the lignification of adjacent cells. Furthermore, SHP1 and SHP2 have shown to play an important role in ovule identity determination. The present work identifies a new function for these two genes in promoting stigma, style and medial tissue development. This new role was discovered by combining the shp1 shp2 double mutant with the aintegumenta (ant) and crabs claw (crc) mutants. In quadruple mutant flowers, the inner whorl is composed of unfused carpels which lack almost completely apical and medial tissues, a phenotype similar to the previously reported fil ant and lug ant double mutants.     

Polar Auxin Transport Is Essential for Medial versus Lateral Tissue Specification and Vascular-Mediated Valve Outgrowth in Arabidopsis Gynoecia

Although it is generally accepted that auxin is important for the patterning of the female reproductive organ, the gynoecium, the flow as well as the temporal and spatial actions of auxin have been difficult to show during early gynoecial development. The primordium of the Arabidopsis (Arabidopsis thaliana) gynoecium is composed of two congenitally fused, laterally positioned carpel primordia bisected by two medially positioned meristematic regions that give rise to apical and internal tissues, including the ovules. This organization makes the gynoecium one of the most complex plant structures, and as such, the regulation of its development has remained largely elusive. By determining the spatiotemporal expression of auxin response reporters and localization of PINFORMED (PIN) auxin efflux carriers, we have been able to create a map of the auxin flow during the earliest stages of gynoecial primordium initiation and outgrowth. We show that transient disruption of polar auxin transport (PAT) results in ectopic auxin responses, broadened expression domains of medial tissue markers, and disturbed lateral preprocambium initiation. Based on these results, we propose a new model of auxin-mediated gynoecial patterning, suggesting that valve outgrowth depends on PIN1-mediated lateral auxin maxima as well as subsequent internal auxin drainage and provascular formation, whereas the growth of the medial domains is less dependent on correct PAT. In addition, PAT is required to prevent the lateral domains, at least in the apical portion of the gynoecial primordium, from obtaining medial fates.The gynoecium is a highly complex assembly comprised of different tissues that work together to support female reproductive competence in angiosperms. As such, studies of the regulatory networks controlling gynoecial development are essential to not only understand plant reproduction, but also increase our knowledge about intertissue-specific cross talk and coordinated development. A gynoecium is composed of one or more carpels, which may have evolved by the invagination of an ancestral leaf-like structure carrying spores along its edges (for review, see Hawkins and Liu, 2014). The Arabidopsis (Arabidopsis thaliana) gynoecium is a bilateral structure composed of two congenitally fused carpels likely derived from the fusion of two leaf-like structures in which the central domains became the lateral valves and the peripheral meristematic margins carrying the ovules became the medial tissues (Hawkins and Liu, 2014). It has been suggested that the medial domains of the Arabidopsis gynoecial primordium are partially differentiated quasi-meristems with maintained meristematic characteristics allowing for prolonged proliferation (Girin et al., 2009). Accordingly, many lateral domain-specific genes are associated with leaf development, while several genes active in the medial domains are related to meristematic activity (Dinneny et al., 2005; Alonso-Cantabrana et al., 2007; González-Reig et al., 2012).Arabidopsis gynoecium development has been described and reviewed extensively (Sessions, 1997; Bowman et al., 1999; Ferrándiz et al., 1999; Balanzá et al., 2006; Østergaard, 2009; Sundberg and Ferrandíz, 2009) and is summarized in Figure 1. Briefly, at early floral stage 5 (stages according to Smyth et al., 1990), after the initiation of outer floral organs, the remaining floral meristem becomes dome shaped. Although the meristem still appears radially symmetric, it is considered to have a medial plane (black dashed lines in Fig. 1) facing the inflorescence meristem and a lateral plane (white dashed lines in Fig. 1) perpendicular to the medial plane. The terminal floral meristem subsequently broadens in the lateral plane, resulting in a bilateral flattened plate (late floral stage 5). At floral stage 6, differential growth has resulted in a central invagination positioned along the lateral plane, and differential gene expressions indicate that initial patterning events distinguishing medial and lateral domains as well as inner (adaxial) and outer (abaxial) tissues have initiated (Bowman et al., 1999). By the end of floral stage 7, the adaxial medial tissues grow toward each other, forming two medial ridges, also called carpel margin meristems (CMMs). The CMMs will give rise to placentae and subsequently ovule primordia at floral stage 8 (Schneitz et al., 1995). By stage 9, the major tissue types of the mature gynoecium become morphologically distinct as the style and stigmatic papillae start to differentiate. Cell differentiation and cell expansion continue during stages 10 to 12, and the gynoecium is fully mature and ready to accept pollen approximately 10 d after it started to initiate from the terminal floral meristem.Open in a separate windowFigure 1.Arabidopsis gynoecium development. Transmitted light confocal images of the remaining floral meristem (stage [st] 5) and the first stages of gynoecial primordia development (stages 6 and 7), and false-colored DIC images of floral stages 8 to 12 gynoecia along a developmental time scale showing the time in days after floral initiation at the end of each stage. Early and late stage 5 as well as upper images at floral stages 6 and 7 are viewed from above. Lower floral stage 6 image is viewed from the lateral side. Lower images of floral stages 7 to 12 gynoecia are viewed from the medial side. Upper images of floral stages 8 to 12 gynoecia show transverse sections. Stages and time scale are adapted after Smyth et al. (1990) and Sessions (1997). White dashed lines indicate lateral plane, black dashed lines indicate medial plane, arrowheads indicate lateral crease, and asterisks indicate CMM. Bars = 10 µm (stages 5–7), 25 µm (stages 8–10), and 50 µm (stages 11 and 12).It is commonly accepted that the plant hormone auxin is important for gynoecium development, and several models have been put forward to explain this on a mechanistic level (Nemhauser et al., 2000; Østergaard, 2009; Sundberg and Østergaard, 2009; Nole-Wilson et al., 2010; Marsch-Martínez et al., 2012; Hawkins and Liu, 2014). However, we still lack a clear picture of the auxin dynamics and response sites during the earliest developmental stages when the major patterning decisions are made. During lateral organ development, instructive auxin peaks or gradients are formed by site-specific auxin biosynthesis and polar auxin transport (PAT), which results in procambium formation, organ outgrowth, and tissue differentiation (Sachs, 1969; Benková et al., 2003; Mattsson et al., 2003; Heisler et al., 2005; Scarpella et al., 2006; Furutani et al., 2014). The plasma membrane-bound PINFORMED (PIN) proteins as well as at least four members of the ATP-binding cassette subfamily B (ABCB)/MULTI-DRUG RESISTANT/P-GLYCOPROTEIN (PGP) protein family show auxin efflux capacity (for review, see Habets and Offringa, 2014). The PIN proteins are often polarly localized at the plasma membrane, whereas the ABCB/PGP proteins are generally localized apolarly. Therefore, the PINs are largely responsible for the net directional flow of auxin, while the ABCB proteins most likely contribute to PAT by regulating the effective cellular auxin available for polar transport (Mravec et al., 2008; Wang et al., 2013). The phytotropin 1-N-naphtylphthalamic acid (NPA) is a well established and widely used PAT inhibitor, although its exact mode of action is obscure (Petrásek et al., 2003). NPA treatment mimics the pin-like shoot phenotype of pin1 loss-of-function mutants (Okada et al., 1991), and even though NPA appears not to directly interact with PIN proteins, it may influence subcellular dynamics and has been shown to bind to ABCB family members, thereby blocking their transport capacity (Noh et al., 2001; Murphy et al., 2002; Geisler et al., 2003; Nagashima et al., 2008; Kim et al., 2010). This suggests that NPA may reduce PAT in part by restricting the amount of auxin available for PIN-mediated polar transport.Although the pin1-1 knockout mutant rarely produces flowers (Okada et al., 1991), gynoecia of the hypomorphic pin1-5 mutant form elongated styles and reduced or even missing carpels (Bennett et al., 1995; Sohlberg et al., 2006). Auxin biosynthesis mutants also produce disproportionate gynoecial tissues (Cheng et al., 2006; Stepanova et al., 2008), suggesting that auxin peaks and fluxes are important for the coordinated development of gynoecial domains. However, because the gynoecium is the last organ to initiate from the floral meristem, the abnormal gynoecial development in auxin-related mutants may result from developmental defects that occurred prior to gynoecium formation. By transiently treating inflorescences with NPA, Nemhauser et al. (2000) showed that PAT in the gynoecial primordia is important for differential development. However, the whole gynoecium was regarded as one entity with apical-basal polarity, and the possibility that the lateral carpels and the medial meristematic tissues could respond differently to the treatment was never discussed. Thus, where and how NPA affects PAT-regulated development has remained elusive.To understand how local auxin activities influence the outgrowth and patterning events of young gynoecial primordia, we determined the localization of PIN and PGP auxin efflux proteins and the resulting auxin response domains. This allowed us to map the directional flow and auxin response peaks during the earliest stages of gynoecium development. In addition, we induced transient disruptions in PAT and assessed the response of auxin signaling and domain-specific markers to establish how auxin signaling and vascular, lateral, and medial domains are affected by alterations in PAT. Based on our data, we propose a new model for auxin-regulated gynoecial patterning in which the medial versus lateral identity is dependent on correct auxin localization, and subsequent carpel valve outgrowth is dependent on transport-mediated apical auxin drainage.     

The zinc finger homeodomain-2 gene of Drosophila controls Notch targets and regulates apoptosis in the tarsal segments

The development of the Drosophila leg is a good model to study processes of pattern formation, cell death and segmentation. Such processes require the coordinate activity of different genes and signaling pathways that progressively subdivide the leg territory into smaller domains. One of the main pathways needed for leg development is the Notch pathway, required for determining the proximo-distal axis of the leg and for the formation of the joints that separate different leg segments. The mechanisms required to coordinate such events are largely unknown. We describe here that the zinc finger homeodomain-2 (zfh-2) gene is highly expressed in cells that will form the leg joints and needed to establish a correct size and pattern in the distal leg. There is an early requirement of zfh-2 to establish the correct proximo-distal axis, but zfh-2 is also needed at late third instar to form the joint between the fourth and fifth tarsal segments. The expression of zfh-2 requires Notch activity but zfh-2 is necessary, in turn, to activate Notch targets such as Enhancer of split and big brain. zfh-2 is controlled by the Drosophila activator protein 2 gene and regulates the late expression of tarsal-less. In the absence of zfh-2 many cells ectopically express the pro-apoptotic gene head involution defective, activate caspase-3 and are positive for acridine orange, indicating they undergo apoptosis. Our results demonstrate the key role of zfh-2 in the control of cell death and Notch signaling during leg development.     

hunchback and Ikaros-like zinc finger genes control reproductive system development in Caenorhabditis elegans

Here we provide evidence for a C2H2 zinc finger gene family with similarity to Ikaros and hunchback. The founding member of this family is Caenorhabditis elegans ehn-3, which has important and poorly understood functions in somatic gonad development. We examined the expression and function of four additional hunchback/Ikaros-like (HIL) genes in C. elegans reproductive system development. Two genes, ehn-3 and R08E3.4, are expressed in somatic gonadal precursors (SGPs) and have overlapping functions in their development. In ehn-3; R08E3.4 double mutants, we find defects in the generation of distal tip cells, anchor cells, and spermatheca; three of the five tissues derived from the SGPs. We provide in vivo evidence that C. elegans HIL proteins have functionally distinct zinc finger domains, with specificity residing in the N-terminal set of four zinc fingers and a likely protein-protein interaction domain provided by the C-terminal pair of zinc fingers. In addition, we find that a chimeric human Ikaros protein containing the N-terminal zinc fingers of EHN-3 functions in C. elegans. Together, these results lend support to the idea that the C. elegans HIL genes and Ikaros have similar functional domains. We propose that hunchback, Ikaros, and the HIL genes arose from a common ancestor that was present prior to the divergence of protostomes and deuterostomes.     

Pollen tube reallocation in two preanthesis cleistogamous species, Ranalisma rostratum and Sagittaria guyanensis ssp. lappula (Alismataceae)

Pollen deposition on stigmas and pollen tube growth in two apocarpous species, Ranalisma rostratum and Sagittaria guyanensis ssp. lappula (Alismataceae), were examined with fluorescence microscopy. The reallocation of pollen tubes among pistils was observed in both species. The percentage of pollinated stigmas per flower was only 22.0% in R. rostratum and 51.0% in S. guyanensis, though the seed/ovule ratios are higher than 65% in both species. The number of pollen grains on each single stigma ranged from 0 to 96 in R. rostratum, and from 0 to 125 in S. guyanensis. When more than one pollen grain deposited on a stigma, all pollen tubes grew to the ovary, but only one of them turned towards the ovule and finally entered the nucleus. The other tubes grew through the receptacle tissue into ovules of adjacent carpels whose stigmas were unpollinated or pollinated later. The intercarpellary growth of pollen tubes could be a mechanism to increase the efficiency of sexual reproduction in an apocarpous gynoecium with low pollination on the pistils.     

uninflatable encodes a novel ectodermal apical surface protein required for tracheal inflation in Drosophila

The tracheal system of Drosophila melanogaster has proven to be an excellent model system for studying the development of branched tubular organs. Mechanisms regulating the patterning and initial maturation of the tracheal system have been largely worked out, yet important questions remain regarding how the mature tubes inflate with air at the end of embryogenesis, and how the tracheal system grows in response to the oxygen needs of a developing larva that increases nearly 1000-fold in volume over a four day period. Here we describe the cloning and characterization of uninflatable (uif), a gene that encodes a large transmembrane protein containing carbohydrate binding and cell signaling motifs in its extracellular domain. Uif is highly conserved in insect species, but does not appear to have a true ortholog in vertebrate species. uif is expressed zygotically beginning in stage 5 embryos, and Uif protein localizes to the apical plasma membrane in all ectodermally derived epithelia, most notably in the tracheal system. uif mutant animals show defects in tracheal inflation at the end of embryogenesis, and die primarily as larvae. Tracheal tubes in mutant larvae are often crushed or twisted, although tracheal patterning and maturation appear normal during embryogenesis. uif mutant larvae also show defects in tracheal growth and molting of their tracheal cuticle.     

Bazooka regulates microtubule organization and spatial restriction of germ plasm assembly in the Drosophila oocyte

Localization of the germ plasm to the posterior of the Drosophila oocyte is required for anteroposterior patterning and germ cell development during embryogenesis. While mechanisms governing the localization of individual germ plasm components have been elucidated, the process by which germ plasm assembly is restricted to the posterior pole is poorly understood. In this study, we identify a novel allele of bazooka (baz), the Drosophila homolog of Par-3, which has allowed the analysis of baz function throughout oogenesis. We demonstrate that baz is required for spatial restriction of the germ plasm and axis patterning, and we uncover multiple requirements for baz in regulating the organization of the oocyte microtubule cytoskeleton. Our results suggest that distinct cortical domains established by Par proteins polarize the oocyte through differential effects on microtubule organization. We further show that microtubule plus-end enrichment is sufficient to drive germ plasm assembly even at a distance from the oocyte cortex, suggesting that control of microtubule organization is critical not only for the localization of germ plasm components to the posterior of the oocyte but also for the restriction of germ plasm assembly to the posterior pole.