Search

Although plants are immobile, many of their organs are flexible to move in response to environmental cues. In dense vegetation, plants detect neighbors through far-red light perception with their leaf tip. They respond remotely, with asymmetrical growth between the abaxial and adaxial sides of the leafstalk, the petiole. This results in upward movement that brings the leaf blades into better lit zones of the canopy. The plant hormone auxin is required for this response, but it is not understood how non-differential leaf tip-derived auxin can remotely regulate movement. Here, we show that remote signaling of far-red light promotes auxin accumulation in the abaxial petiole. This local auxin accumulation is facilitated by reinforcing an intrinsic directionality of the auxin transport protein PIN3 on the petiole endodermis, as visualized with a PIN3-GFP line. Using an auxin biosensor, we show that auxin accumulates in all cell layers from endodermis to epidermis in the abaxial petiole, upon far-red light signaling in the remote leaf tip. In the petiole, auxin elicits a response to both auxin itself as well as a second growth promoter; gibberellin. We show that this dual regulation is necessary for hyponastic leaf movement in response to light. Our data indicate that gibberellin is required to permit cell growth, whereas differential auxin accumulation determines which cells can grow. Our results reveal how plants can spatially relay information about neighbor proximity from their sensory leaf tips to the petiole base, thus driving adaptive growth.

The study aim was to determine prevalence and predictors of life satisfaction in New Zealand. In this observational cross-sectional study, a sample of 10,799 participants from NZ were drawn from the Gallup World Poll from 2006 to 2017. Data were analysed using regression analysis and ANOVA. Prevalence of life satisfaction across time varied little from a high of 7.61 (SD = 1.6) in 2007 to a low of 7.23 (SD = 1.73) in 2011 (range 0-10). Satisfaction with standards of living predicted life satisfaction regardless of age or gender. For males across all age groups and females up to age 40 years, positive experiences and satisfaction with household income were important predictors. Being married was an important predictor for males over 40 years and feeling satisfied with their current city was important for females across all ages and for men under 40. The levels of life satisfaction changed over time, possibly due to major national events. Satisfaction with standards of living was found to predict life satisfaction regardless of age or gender. These results provide a path for policy focus towards increased life satisfaction.

According to Self-Determination Theory, need-supportive teaching fosters students’ motivation. The present study examined the interplay between the three dimensions of need support: autonomy support, structure, and involvement. Using both student and teacher-reports (N = 287 Grade 7 students), configurations of need support were examined with Latent Profile Analyses. Balanced profiles were identified based on student reports (low, moderate, or high need support), while unbalanced profiles were identified based on student-specific teacher-reports. Higher levels of need support were associated with more motivation and achievement, while high levels of teacher-reported structure and involvement could not compensate for a lack of teacher-reported autonomy support.

The plant hormone auxin is a key regulator of many growth and developmental processes. The presence of auxin  changes the gene expression of the cell via a short pathway called the nuclear auxin pathway (NAP). The NAP contains three players: TIR1/AFB, Aux/IAA and the transcription factor ARF. Under conditions of low auxin,  Aux/IAA binds ARF repressing it. At higher concentrations of auxin, TIR1/AFB binds Aux/IAA and marks it for degradation, thereby freeing ARF. Members of the ARF family bind a DNA motif called AuxRE (TGTCTC) and their DNA binding domains (DBDs) are known to dimerize and bind cooperatively on response elements composed by two AuxREs present in an inverted orientation. Although the affinities at play inside the NAP and between ARFs and AuxREs had been studied extensively with a range of techniques,  a quantitative view on this system was still lacking. Throughout this thesis, we therefore developed and applied methods with the goal of obtaining a quantitative understanding of ARF-ARF and ARF-AuxRE interactions.In chapter 2 we developed and utilized a method based on smFRET and smPIFE-FRET to study the interaction between ARF and composite DNA response elements. We tested several A. thaliana ARF-DBDs and showed that the differences in binding stability and kinetics are quantitatively captured by the method. The smFRET and smPIFE-FRET experiments in which  the affinity of a DNA-binding deficient mutant of AtARF5-DBD (R215A) was probed, proved that the shift in FRET efficiency seen when wt AtARF5-DBD is added in concentration of tens on nM is due to the specific protein interaction with the DNA motif. We then tested the binding preferences of Marchantia polymorpha ARF1 and ARF2, which are, respectively, the only members of the phylogenetically conserved class A-ARF and B-ARF in the species. Whereas A-ARFs are considered   activators, B-ARFs are considered repressors. In M.  polymorpha, a  mechanism in which B-ARF

Background According to self‐determination theory, teachers can support their students’ engagement in learning by providing autonomy support and structure. Within classes, however, there appears to be great diversity in the extent to which students experience autonomy and structure. Aims This study aimed to investigate the degree to which teachers’ perceptions of student‐specific autonomy support and structure differ between students in their class and whether differentiated need support predicts students’ motivation. Sample Twenty‐four elementary school teachers and their students (n = 506) participated in this study. Method Teachers completed a short questionnaire assessing their perceptions of autonomy support and structure for each student. Students completed two questionnaires assessing perceptions of need support and their motivation. Multilevel analyses were conducted. Results The results showed that the within‐classroom variation in both teacher perceptions and student perceptions of need support was considerably larger than the between‐classroom variation. Teacher perceptions of student‐specific autonomy support were positively associated with students’ autonomous motivation and negatively with students’ controlled motivation. However, teacher perceptions of student‐specific structure were positively associated with students’ controlled motivation. Conclusions These findings suggest that teachers differentiate in need support. The positive association between teacher perceptions of structure and students’ controlled motivation might suggest that teachers may offer structure in controlling rather than autonomy‐supportive ways. Furthermore, the relations between need support and students’ motivation differed between the class‐level and the within‐class (student) level highlighting the need for disentangling the effects of need‐supportive teaching at different levels and adopting a multilevel

Contains fulltext : 220423.pdf (Publisher’s version ) (Closed access), CNOT1 is a member of the CCR4-NOT complex, which is a master regulator, orchestrating gene expression, RNA deadenylation, and protein ubiquitination. We report on 39 individuals with heterozygous de novo CNOT1 variants, including missense, splice site, and nonsense variants, who present with a clinical spectrum of intellectual disability, motor delay, speech delay, seizures, hypotonia, and behavioral problems. To link CNOT1 dysfunction to the neurodevelopmental phenotype observed, we generated variant-specific Drosophila models, which showed learning and memory defects upon CNOT1 knockdown. Introduction of human wild-type CNOT1 was able to rescue this phenotype, whereas mutants could not or only partially, supporting our hypothesis that CNOT1 impairment results in neurodevelopmental delay. Furthermore, the genetic interaction with autism-spectrum genes, such as ASH1L, DYRK1A, MED13, and SHANK3, was impaired in our Drosophila models. Molecular characterization of CNOT1 variants revealed normal CNOT1 expression levels, with both mutant and wild-type alleles expressed at similar levels. Analysis of protein-protein interactions with other members indicated that the CCR4-NOT complex remained intact. An integrated omics approach of patient-derived genomics and transcriptomics data suggested only minimal effects on endonucleolytic nonsense-mediated mRNA decay components, suggesting that de novo CNOT1 variants are likely haploinsufficient hypomorph or neomorph, rather than dominant negative. In summary, we provide strong evidence that de novo CNOT1 variants cause neurodevelopmental delay with a wide range of additional co-morbidities. Whereas the underlying pathophysiological mechanism warrants further analysis, our data demonstrate an essential and central role of the CCR4-NOT complex in human brain development.

The plant hormone auxin profoundly affects many aspects of plant growth and development. Since its discovery, the pathway leading to alteration in gene expression has been well documented. Strikingly, this nuclear auxin pathway (NAP) is short and consist of only three dedicated components, the SCF TIR1/AFB auxin receptor complex, AUX/IAA co-repressors and the auxin transcription factors (ARFs). Due to the simplicity of this pathway, a major question in the auxin field is how specificity is determined. In Chapter 1, I provide an introduction of the NAP, other physiological effects elicited by auxin, and how proteomic approaches might shed more light on auxin signalling.In Chapter 2, we provide a deeper insight into ARFs by dissecting and highlighting current views on ARF functioning. Since ARFs are the direct output of the NAP, we reason that the specificity within auxin signalling must be controlled by ARFs. Numerous aspects of ARF functioning may contribute to specificity. This can be deducted from specific cellular expression of ARFs, the promotor architecture where ARFs bind to, the combinatorial interactions amongst the NAP components and the functioning of ARF domains. We highlight that, although the DBD and PB1 domains of ARFs have been structurally and to some extent functionally resolved, the specificity in ARF functioning might reside in the middle region. From predictions, it appears that the middle region is intrinsically disordered. This might provide a signalling hub for ARF functioning. Intrinsically disordered regions have no structure but can provide platforms for co-factor interactions. That ARF co-factors are important for auxin output has been reported in a scattered fashion and is not clearly documented. We therefore, in Chapter 3, investigated which co-factors interact with ARFs. We utilized an unbiased quantitative affinity purification mass spectrometry approach to decipher the ARF interactome. Initial strategies utilizing conventional AP

Land plants can grow to exceptional body sizes, with the most complex specialized structures. Directional cell division has a fundamental role throughout the tremendous plant growth processes, yet its molecular regulation is still largely unknown. Chapter 1 of this thesis discusses mechanisms and sub-cellular structures known to be involved in plant cell division orientation control, and explores tools used for dissection of this complex mechanism.Dissecting the complex plant cell division control mechanisms requires a simple and highly predictable in vivo model system. The highly predictable a relatively simple development of the Arabidopsis embryo makes it suitable for studying plant cell division regulation. In Chapter 2, we explore the cellular basis -, cell division patterns -, and regulatory pathways underlying early plant embryogenesis. We describe previous research showing that most cell divisions in the Arabidopsis embryo divide according a geometry- based “shortest-wall” principle, except for formative, asymmetric divisions. When auxin- signalling is disabled by overexpression of the dominant negative response inhibitor BODENLOS (BDL; bdl-mutant) all divisions in the embryo switch to “shortest-wall” divisions, suggesting auxin-signalling based control of oriented cell divisions.Since the microtubule (MT) cytoskeleton is a possible factor regulating cell division orientation downstream of auxin, dissecting its dynamics and regulatory mechanisms is crucial to understand cell division regulation. Combining high-resolution imaging of cell walls and MTs with a modelling strategy for MT organisation, in Chapter 3, we show that the cortical MT array is crucial for division plane orientation control in de Arabidopsis embryo. In our model, MT-dynamics are confined by cell shape -, MT stability at cell edges-, and local MT stability by auxin. Additionally, comparison of cell-biology in wild-type - and bdl-mutant embryos in Chapter 4 reveals that F-actin organisation

Auxin is a key phytohormone for growth and development across many plant species. With the advances in next-generation sequencing, and ever-growing genomes and transcriptomes in the last decade, helped us infer the detailed origin and evolution of auxin biology in this thesis. We have developed a simple yet effective methodology to reconstruct the origin and evolution of various genes families across all plant lineages, including the algal ancestors. We first tested this protocol to study the evolution of auxin biosynthesis gene families Tryptophan aminotransferase of Arabidopsis (TAA) and YUCCA (YUC). Further, we exploited the evolution of Gretchen Hagen 3 (GH3) protein family involved in the auxin homeostasis that conjugate amino acids to hormones. Moreover, we also showed that this method could be applied to proteins with unknown or novel domains, by studying the evolution and annotation of SOSEKI (SOK) proteins. Auxin elicit both genomic and non-genomic responses, through nuclear auxin pathway (NAP) and Auxin binding protein 1 (ABP1), respectively. Hence, we also studied the origin and evolution of ABP1 as well as Auxin Response Factor (ARF), Auxin/Indole-3-acetic acid (Aux/IAA) and Transport inhibitor response 1/Auxin-signaling F-box (TIR1/AFB) gene families of NAP. A key step in the nuclear auxin pathway, is the interaction between ARF and Aux/IAA proteins through C-terminal Phox and Bem1 (PB1) domain. As PB1 domain is also identified in protozoans, fungi as well as in animals, we studied if the PB1 domain is originated in Last Eukaryote Common Ancestor (LECA). The results in this thesis collectively show the step-wise origins of auxin biology in green algae and subsequent functionality in land plants. We also highlighted questions that still remain and synchronize these findings with the on-going efforts to understand ‘non-canonical’ routes of auxin action in plants.

This review focuses on the evolution of plant hormone signaling pathways. Like the chemical nature of the hormones themselves, the signaling pathways are diverse. Therefore, we focus on a group of hormones whose primary perception mechanism involves an Skp1/Cullin/F-box-type ubiquitin ligase: auxin, jasmonic acid, gibberellic acid, and strigolactone. We begin with a comparison of the core signaling pathways of these four hormones, which have been established through studies conducted in model organisms in the Angiosperms. With the advent of next-generation sequencing and advanced tools for genetic manipulation, the door to understanding the origins of hormone signaling mechanisms in plants beyond these few model systems has opened. For example, in-depth phylogenetic analyses of hormone signaling components are now being complemented by genetic studies in early diverging land plants. Here we discuss recent investigations of how basal land plants make and sense hormones. Finally, we propose connections between the emergence of hormone signaling complexity and major developmental transitions in plant evolution.

The complex nature of mental well-being is reflected in the great diversity of variables thought to represent aspects of mental flourishing. Discovering the underlying structure of mental well-being is important for a full understanding of this complex construct. Using data from 3 countries (the United States, Japan, and Iran), we performed multi-dimensional scaling to analyze the representation of 9 hedonic and eudaimonic well-being variables in a 2-dimensional psychological space. The analyses revealed 2 interpretable underlying dimensions across cultures and gender groups. The first dimension-eudaimonic well-being versus hedonic well-being-is well-known to well-being researchers. The second dimension-existential relatedness versus Epicurean independence-has not been recognized before. Existential relatedness is the characteristic of being meaningfully interconnected with things other than oneself, and is mainly based on the variables positive relations with others, personal growth, purpose in life, and life satisfaction. Epicurean independence is the characteristic of being relatively free of painful experiences and not feeling the need to have ones' views accepted by anyone but oneself. Epicurean independence is mainly based on the variables autonomy and absence of negative affect. We explain these dimensions in detail and discuss the implications for well-being research and policy.

During plant embryogenesis, the future body plan of the plant is laid down. Part of this development is the specification of cell identities: the outer epidermis, the middle ground tissue and the inner vascular cells. In this thesis we have looked at the genetic components that control plant vascular identity. We have traced back the first vascular cells to the 16-cell embryo and discovered that the development of vascular identity is not a single step but rather a multi-step process. Upstream of this multi-step process we discovered a large set of candidate regulators that control vascular identity. After focusing one of these candidates we now hypothesize that the protein GBF2 can regulate vascular gene expression. Together with proteins that act downstream of the plant hormone auxin, GBF2 interacts with specific DNA sequences to regulate the initiation of vascular development.

The emergence of vascular plants (Tracheophytes) has had great impacts on our planet and now make up the majority of the biomass on Earth. The innovation of vascular tissues in plants allowed the colonization of a larger habitats and subsequently created the opportunity for new ecosystems to arise. Vascular tissues can thus be regarded as one of the key evolutionary innovations in the plant lineage. Yet, the molecular innovations that led to the evolution of these conductive tissues are unknown. Here, we reveal the evolutionary trajectory for the heterodimeric TMO5/LHW transcription factor complex, which is rate-limiting for vascular cell proliferation in Arabidopsis thaliana. We show that both regulators have origins predating vascular tissue emergence, and even terrestrialization. We further show that TMO5 evolved its modern function at the origin of land plants, by mutations in the DNA-binding region of the bHLH domain. An innovation in LHW, coinciding with vascular plant emergence, conditioned obligate heterodimerization and generated the critical function in vascular development. In summary, our results suggest that division potential of vascular cells may have been an important factor contributing to the evolution of vascular plants.

Land plants can reproduce sexually by developing an embryo from a fertilized egg cell. However, embryos can also be formed from other cell types in many plant species. A key question is thus how embryo identity in plants is controlled, and how this process is modified during non-zygotic embryogenesis. The Arabidopsis zygote divides to produce an embryonic lineage and an extra-embryonic suspensor. Yet, normally quiescent suspensor cells can develop a second embryo when the initial embryo is damaged, or when response to the signaling molecule auxin is locally blocked. Here we have used auxin-dependent suspensor embryogenesis as a model to determine transcriptome changes during embryonic reprogramming. We find that reprogramming is complex and accompanied by large transcriptomic changes prior to anatomic changes. This analysis revealed a strong enrichment for genes encoding components of auxin homeostasis and response among misregulated genes. Strikingly, deregulation among multiple auxin-related gene families converged upon re-establishment of cellular auxin levels or response. This suggests a remarkable degree of feedback regulation to create resilience in auxin response during embryo development. Starting from the transcriptome of auxin-deregulated embryos, we identify an auxin-dependent bHLH transcription factor network that mediates the activity of this hormone in suppressing embryo development from the suspensor.

The evolution of multi-cellular plants went hand in hand with the establishment of a complex polarity system to guide development and survival. Within the cell, polarity cues need to be established, read and translated into sub-cellular processes. Yet, the exact mechanisms that translate polarity into sub-cellular processes remain elusive. In Chapter 1, we discuss polarity and several proteins that use polar information to guide their localization.  The Arabidopsis embryo is introduced as an excellent model for studying cell polarity.In Chapter 2, we take a closer look at development of the Arabidopsis embryo. Hereby we focus specifically on how oriented divisions are generated by developmental regulators and the division machinery. Recent advancement in 3D imaging of the embryo revealed that cell division abides to a ‘smallest plane’ rule, and that auxin can prevent adherence to this rule.  Studying how auxin effectors are linked to cell division regulators and cell polarity may provide a greater understanding of oriented cell division in the embryo.Using the Arabidopsis embryo as model for auxin-regulated development, we identify a novel family of polarly localized proteins in Chapter 3. Unlike previously published polar proteins, this new family shows a robust localization to specific cell edges, which coined the name SOSEKI (SOK, Japanese for cornerstone). SOK localization is guided by integration of plant-wide apico-basal and radial polarity. Pharmacological inhibition of pathways commonly used by polarly localized proteins showed that SOK is localized through a novel mechanism. Mis-expression of SOK1 caused oblique cell divisions and polar localization was required for this activity. We identified a highly conserved N-terminal domain that structurally resembles the DIX domain found in Wnt polarity signalling proteins in animals (Ehebauer & Arias, 2009; Schwarz-Romond et al., 2007). In animals, this domain shows autocatalytic polymerization. SOK1 DIX

A fundamental question in developmental biology is how the complex cellular pattern in multicellular organisms arises from a single cell. In land plants, the biosynthesis, transport, and signaling of phytohormone auxin is essential for pattern formation in embryogenesis. In Chapter 1, a brief introduction on plant embryogenesis, the roles of auxin signaling in pattern formation in early embryo, cellular basis on oriented cell division, and auxin-regulated oriented cell division during early embryogenesis are described as the foundation of this thesis aimed to answer the domain and cellular structures regulated by auxin that lead precise pattern formation during early embryo development of Arabidopsis thaliana. In Chapter 2, two novel fluorescent protein-based reporters for auxin perception and response, respectively, were developed to overcome technical bottlenecks for dissecting auxin signaling in embryos. The novel reporters offer higher sensitivity and responsiveness compared to existing tools. Our reporters revealed the gradients and maxima of auxin perception and response that had been hypothesized, but not yet detected. In addition, these new tools now offer a wider scope of application beyond the embryo and are generic tools for the auxin biology research community. In Chapter 3, the auxin reporters described in the previous chapter were improved to overcome their limitations, and the first comprehensive auxin reporter that was able to simultaneously visualize both auxin perception and response was characterized. With this new auxin reporter, the differential auxin signaling capacity between different cell types and differentiation states was demonstrated. In addition, the reporter for auxin response described in the previous chapter was applied in mutant embryos with a local auxin response defect, revealing its broad impact on auxin output. In Chapter 4, a toolkit of fluorescent protein-based markers labeling specific cellular structures was established. The

Growth of plants depends on cell division and elongation of the divided cells. After cell division, plant cells are fixed immediately within their tissue context. Thus, a carefully positioning and orientation of the division plane is crucial for plants to properly pattern and grow. Anticlinal cell divisions result in more cells within a cell file and lead to longitudinal growth; while periclinal and radial divisions (PRD) result in the addition of cell files during radial growth. So far, how a cell controls the position and orientation of its division plane remains poorly understood. In this thesis we focused on a complex of two proteins called TMO5 and LHW that are capable of shifting the division plane orientation towards PRD. Our main aim was to identify which genes are activated by the TMO5/LHW complex and characterize these to understand how plant cells control the positioning and orientation of their cell divisions to allow normal growth. After introducing the main concepts and background information in Chapter 2, we continue to show in Chapter 3 how we generated and characterized an inducible line of TMO5 and LHW (dGR). We compared this line to the existing TMO5-LHW misexpression and overexpression lines and concluded we created an excellent tool to study cell division orientation. Because TMO5 and LHW are transcription factors, we next studied the transcriptional changes upon induction. While it is commonly assumed that the plant hormone cytokinin is required to control these divisions, we could prove that indeed cytokinin response is triggered upon induction of TMO5/LHW. In Chapter 4 we used the transcriptional data to select putative targets, which were verified using a misexpression screen. We identified DOF2.1 as a factor capable of inducing PRD and continued to show how DOF2.1 functions downstream of TMO5-LHW and controls division plane orientation during vascular development. Analysis of loss-of-function mutants of DOF2.1 and the two closest family mem

Growth of plant tissues and organs depends on continuous production of new cells, by niches of stem cells. Stem cells typically divide to give rise to one differentiating daughter and one non-differentiating daughter. This constant process of self-renewal ensures that the niches of stem cells or meristems stay active throughout plant-life. Specification of stem cells occurs very early during development of the emrbyo and they are maintained during later stages. The Arabidopsis embryo is a highly predictable and relatively simple model to study several developmental processes. Chapter 1 discusses the Arabidopsis embryo as a model for development and morphogenesis and describes the currently known factors involved in these processes. Molecular cloning is a vital technique of today’s plant biological research. The ability to quickly produce reliable constructs for follow-up analyses can greatly accelerate biological research. In Chapter 2, we describe the optimization of a highly efficient Ligation Independent Cloning method. This method makes use of sticky overhangs that enable in vivo ligation of cloning products. We present a step-by-step protocol that enables generating plant transformation-ready constructs in a semi-high-throughput manner, within two to three days. This method can for example facilitate follow-up analysis of genome-wide approaches. Proteins regularly function as part of larger protein-complexes and their interaction partners can often be indicative of functionality. Unbiased, in vivo analysis of protein complexes can therefore be very informative for the functional characterization of a protein of interest. In Chapter 3, we describe an optimized method for immunoprecipitation followed by tandem mass-spectrometry. By performing mass-spectrometry measurements on at least three biological replicates, relative abundance of proteins in GFP-tagged sample compared to background controls can be statistically evaluated to identify high-confidence interacto

Control of tissue dimensions in multicellular organisms requires the precise quantitative regulation of mitotic activity. In plants, where cells are immobile, tissue size is achieved through control of both cell division orientation and mitotic rate. The bHLH transcription factor heterodimer formed by TARGET OF MONOPTEROS5 (TMO5) and LONESOME HIGHWAY (LHVV) is a central regulator of vascular width-increasing divisions. An important unanswered question is how its activity is limited to specify vascular tissue dimensions. Here we identify a regulatory network that restricts TMO5/LHW activity. We show that thermospermine synthase ACAULIS5 antagonizes TMO5/LHW activity by promoting the accumulation of SAC51-LIKE (SACL) bHLH transcription factors. SACL proteins heterodimerize with LHW therefore likely competing with TMO5/LHW interactions prevent activation of TMO5/LHW target genes, and suppress the over-proliferation caused by excess TMO5/LHW activity. These findings connect two thus-far disparate pathways and provide a mechanistic understanding of the quantitative control of vascular tissue growth.

The plant hormone auxin and its directional transport are known to play a crucial role in defining the embryonic axis and subsequent development of the body plan. Although the role of PIN auxin efflux transporters has been clearly assigned during embryonic shoot and root specification, the role of the auxin influx carriers AUX1 and LIKE-AUX1 (LAX) proteins is not well established. Here, we used chemical and genetic tools on Brassica napus microspore-derived embryos and Arabidopsis thaliana zygotic embryos, and demonstrate that AUX1, LAX1 and LAX2 are required for both shoot and root pole formation, in concert with PIN efflux carriers. Furthermore, we uncovered a positive-feedback loop betweenMONOPTEROS(ARF5)- dependent auxin signalling and auxin transport. ThisMONOPTEROSdependent transcriptional regulation of auxin influx (AUX1, LAX1 and LAX2) and auxin efflux (PIN1 and PIN4) carriers by MONOPTEROS helps to maintain proper auxin transport to the root tip. These results indicate that auxin-dependent cell specification during embryo development requires balanced auxin transport involving both influx and efflux mechanisms, and that this transport is maintained by a positive transcriptional feedback on auxin signalling.

Embryogenesis is the beginning of plant development, yet the cell fate decisions and patterning steps that occur during this time are reiterated during development to build the post-embryonic architecture. In Arabidopsis, embryogenesis follows a simple and predictable pattern, making it an ideal model with which to understand how cellular and tissue developmental processes are controlled. Here, we review the early stages of Arabidopsis embryogenesis, focusing on the globular stage, during which time stem cells are first specified and all major tissues obtain their identities. We discuss four different aspects of development: the formation of outer versus inner layers; the specification of vascular and ground tissues; the determination of shoot and root domains; and the establishment of the first stem cells.

The auxin receptor TIR1 is an F-box protein functioning in a ubiquitin ligase complex to target repressors for degradation. It is itself an unstable protein, but newly identified mutations protect both TIR1 and its substrates from degradation. These mutations could help in identifying the substrates for hundreds of other F-box proteins.