SHAGGY-like kinase 12 regulates flowering through mediating CONSTANS stability in Arabidopsis

Photoperiod is a major environmental cue that determines the floral transition from vegetative to reproductive development in flowering plants. Arabidopsis thaliana responds to photoperiodic signals mainly through a central regulator CONSTANS (CO). Although it has been suggested that phosphorylation of CO contributes to its role in photoperiodic control of flowering, how this is regulated so far remains unknown. Here, we report that a glycogen synthase kinase-3 member, SHAGGY-like kinase 12 (SK12), plays an important role in preventing precocious flowering through phosphorylating CO. Loss of function of SK12 causes early flowering. SK12 expression in seedlings is decreased during the floral transition, and its expression in vascular tissues is required for repressing flowering. SK12 interacts with and phosphorylates CO at threonine 119, thus facilitating CO degradation. Our findings suggest that site-specific phosphorylation of CO by SK12 is critical for modulating the photoperiodic output for the floral induction in Arabidopsis.

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Calibration of LgrassFlo, a new model of perennial grass phenology in response to temperature and photoperiod.

10.5194/egusphere-egu21-12430 ◽

2021 ◽

Author(s):

Simon Rouet ◽

Jean-Louis Durand ◽

Didier Combes ◽

Abraham Escobar-Gutierrez ◽

Romain Barillot

Keyword(s):

Genetic Diversity ◽

Plant Architecture ◽

Floral Induction ◽

Perennial Grass ◽

Heading Date ◽

Reproductive Development ◽

Perennial Grasses ◽

Floral Transition ◽

New Model ◽

Primary Induction

In perennial grasses, the reproductive development encompasses several phenological events, such as apex induction, floral transition, heading and flowering, that deeply affect biomass production, forage quality and plant perenniality. Despite the importance of perennial grasses in agricultural systems and natural ecosystems, we still lack accurate models predicting the reproductive development and its consequences on plant growth and grassland management. Most of available models implements a fixed scheduling of the reproductive development expressed either in thermal time or in calendar time. The progressive completion of floral induction and the effects of environmental factors are generally poorly described. In addition, the vegetative and reproductive developments are represented as independent and successive phases. In the present work, we introduce the new model LgrassFlo, which simulates the reproductive development of perennial grasses in interaction with plant vegetative development and considering the effects of environmental conditions on floral induction.LgrassFlo simulates the canopy as the dynamics of a collection of individual plants, each being composed of one or more tillers. The 3D description of leaf growth and tillering is based on a functional-structural plant model of perennial ryegrass (Lgrass). We developed a new model of floral induction describing the progression of the primary and secondary induction of each apex of the plant according to (i) the daily temperature, (ii) photoperiod and (iii) plant architecture. This model was coupled to Lgrass, the model ensemble being called LgrassFlo. During apex induction, LgrassFlo accounts for an increase in the rates of leaf primordia initiation and leaf elongation. After floral transition, we assume that the apex only initiates spikelet primordia and that internodes start to elongate. LgrassFlo simulates the date of floral transition, the final number of leaves and the heading date based on a 3D representation of plant architecture.A specific experiment was carried out in order to calibrate LgrassFlo on data describing the vegetative and reproductive development of three Lolium perenne cultivars contrasted for their precocity and exposed to four inductive conditions in growth chambers. The first three conditions consisted in a period allowing for primary induction (low temperature &#8211; short day) followed by a period allowing for secondary induction (high temperature &#8211; long day), the two periods being spaced by a non-inductive period (high temperature - short day) of 0, 3 or 6 weeks. In the fourth condition, plants were not exposed to conditions allowing for the primary induction. A set of vegetative and reproductive parameters were estimated for each individual plant of the experiment. The parameter values were independent of the experimental treatment but showed a large genetic diversity both between and within varieties. Using this calibration, LgrassFlo satisfactorily predicted the observed diversity in final leaf number and heading date.The present model is a step forward towards a better prediction of perennial grass phenology in actual and future climatic conditions. In this respect, the model is being currently used to simulate the observed genetic diversity in the heading date of several Lolium perenne cultivars grown in contrasted temperate climates over the last 15 years.

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Cytokinin signalling regulates two-stage inflorescence arrest in Arabidopsis

10.1101/2022.01.06.475268 ◽

2022 ◽

Author(s):

Catriona H Walker ◽

Alexander Ware ◽

Jan Šimura ◽

Karin Ljung ◽

Zoe A Wilson ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Reproductive Success ◽

Flowering Plants ◽

Loss Of Function ◽

Inflorescence Meristem ◽

Fruit Removal ◽

Cytokinin Receptor ◽

Developmental Arrest ◽

Cytokinin Treatment ◽

Floral Primordia

To maximise their reproductive success, flowering plants must correctly time their entry into and exit from the reproductive phase (flowering). While much is known about the mechanisms that regulate the initiation of flowering, the regulation of end-of-flowering remains largely uncharacterised. End-of-flowering in Arabidopsis thaliana consists of the quasi-synchronous arrest of individual inflorescences, but it is unclear how this arrest is correctly timed with respect to environmental stimuli and ongoing reproductive success. Here we show that Arabidopsis inflorescence arrest is a complex developmental phenomenon which includes a decline in size and cessation of activity in the inflorescence meristem (IM), coupled with a separable developmental arrest in all unopened floral primordia (floral arrest); these events occur well before the visible arrest of the inflorescence. We show that global removal of inflorescences can delay both IM arrest and floral arrest, but that local fruit removal only delays floral arrest, emphasising the separability of these processes. We test a role for cytokinin in regulating inflorescence arrest, and find that cytokinin treatment can delay arrest. We further show that gain-of-function cytokinin receptor hypersensitive mutants can delay floral arrest, and also IM arrest, depending on the expression pattern of the receptor; conversely, loss-of-function mutants prevent extension of flowering in response to inflorescence removal. Collectively, our data suggest that the dilution of cytokinin among an increasing number of sink organs leads to end-of-flowering in Arabidopsis by triggering IM and floral arrest, conversely meaning that a lack of reproductive success can homeostatically extend flowering in compensation.

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Integrated dominance mechanisms regulate reproductive architecture in Arabidopsis thaliana and Brassica napus

Plant Physiology ◽

10.1093/plphys/kiab194 ◽

2021 ◽

Author(s):

Catriona H Walker ◽

Cara D Wheeldon ◽

Tom Bennett

Keyword(s):

Arabidopsis Thaliana ◽

Brassica Napus ◽

Resource Use ◽

Reproductive Effort ◽

Seed Set ◽

Developmental Stages ◽

Reproductive Development ◽

Flowering Plants ◽

Negative Feedbacks ◽

Spatio Temporal

Abstract The production of seed in flowering plants is complicated by the need to first invest in reproductive shoots, inflorescences, flowers and fruit. Furthermore, in many species, it will be months between plants generating flowers and setting seed. How can plants therefore produce an optimal seed-set relative to environmental resources when the ‘reproductive architecture’ that supports seed-set needs to be elaborated so far in advance? Here, we address this question by investigating the spatio-temporal control of reproductive architecture in Arabidopsis (Arabidopsis thaliana) and Brassica napus. We show that resource- and resource-related signals such as substrate volume play a key role in determining the scale of reproductive effort, and that this is reflected in the earliest events in reproductive development, which broadly predicts the subsequent reproductive effort. We show that a series of negative feedbacks both within and between developmental stages prevent plants from over-committing to early stages of development. These feedbacks create a highly plastic, homeostatic system in which additional organs can be produced in the case of reproductive failure elsewhere in the system. We propose that these feedbacks represent an ‘integrated dominance’ mechanism that allows resource use to be correctly sequenced between developmental stages to optimise seed set.

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MIR822 modulates monosporic female gametogenesis through an ARGONAUTE9-dependent pathway in Arabidopsis thaliana

10.1101/2021.10.18.464879 ◽

2021 ◽

Author(s):

ANDREA TOVAR AGUILAR ◽

Daniel GRIMANELLI ◽

Gerardo Acosta Garcia ◽

Jean Philippe Vielle Calzada ◽

Jesus Agustin Badillo-Corona ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Molecular Mechanisms ◽

Target Genes ◽

Flowering Plants ◽

Loss Of Function ◽

Genes Encoding ◽

Functional Megaspore ◽

Dependent Pathway ◽

Female Gametogenesis

In the ovule of flowering plants, the establishment of the haploid generation occurs when a somatic cell differentiates into a Megaspore Mother Cell (MMC) and initiates meiosis. As most flowering plants, Arabidopsis thaliana undergoes a monosporic type of gametogenesis; three meiotically derived cells degenerate without further division, and a single one, the functional megaspore (FM), divides mitotically to form the female gametophyte. In Arabidopsis, the ARGONAUTE4 clade proteins are involved in the control of megasporogenesis. In particular, mutations in ARGONAUTE9 (AGO9) lead to the ectopic differentiation of gametic precursors that can give rise female gametophytes. However, the genetic basis and molecular mechanisms that control monosporic gametogenesis remain largely unknown. Here, we show that Arabidopsis plants carrying loss-of-function mutations in the AGO9-interacting miR822a give rise to extranumerary surviving megaspores that acquire a FM identity and divide without giving rise to differentiated female gametophytes. The overexpression of three miR822a target genes encoding Cysteine/Histidine-Rich C1 domain proteins (DC1) phenocopy mir822a plants. The miR822a targets are overexpressed in ago9 mutant ovules, confirming that miR822a acts through an AGO9-dependent pathway to negatively regulate DC1 domain proteins. Our results identify a new role of miRNAs in the most prevalent form of female gametogenesis in flowering plants

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α-Synuclein Induces the GSK-3-Mediated Phosphorylation and Degradation of NURR1 and Loss of Dopaminergic Hallmarks

Molecular Neurobiology ◽

10.1007/s12035-021-02558-9 ◽

2021 ◽

Author(s):

Ángel Juan García-Yagüe ◽

Isabel Lastres-Becker ◽

Leonidas Stefanis ◽

Demetrios K. Vassilatis ◽

Antonio Cuadrado

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Dopaminergic Neurons ◽

Glycogen Synthase ◽

Single Point ◽

Mechanistic Explanation ◽

Substantia Nigra Pars Compacta ◽

Glycogen Synthase Kinase 3 ◽

Deletion Mutants ◽

Loss Of Function

Abstract In Parkinson’s disease, the dysfunction of the dopaminergic nigrostriatal tract involves the loss of function of dopaminergic neurons of the substantia nigra pars compacta followed by death of these neurons. The functional recovery of these neurons requires a deep knowledge of the molecules that maintain the dopaminergic phenotype during adulthood and the mechanisms that subvert their activity. Previous studies have shown that transcription factor NURR1, involved in differentiation and maintenance of the dopaminergic phenotype, is downregulated by α-synuclein (α-SYN). In this study, we provide a mechanistic explanation to this finding by connecting α-SYN-induced activation of glycogen synthase kinase-3 (GSK-3) with NURR1 phosphorylation followed by proteasomal degradation. The use of sequential deletion mutants and single point mutants of NURR1 allowed the identification of a domain comprising amino acids 123-PSSPPTPSTPS-134 that is targeted by GSK-3 and leads to subsequent ubiquitination and proteasome degradation. This study provides a detailed analysis of the regulation of NURR1 stability by phosphorylation in synucleinopathies such as Parkinson’s disease. Graphical abstract

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Systematic analyses of the MIR172 family members of Arabidopsis define their distinct roles in regulation of APETALA2 during floral transition

PLoS Biology ◽

10.1371/journal.pbio.3001043 ◽

2021 ◽

Vol 19 (2) ◽

pp. e3001043

Author(s):

Diarmuid S. Ó’Maoiléidigh ◽

Annabel D. van Driel ◽

Anamika Singh ◽

Qing Sang ◽

Nolwenn Le Bec ◽

...

Keyword(s):

Arabidopsis Thaliana ◽

Gene Regulatory Networks ◽

Shoot Apex ◽

Regulatory Networks ◽

Floral Induction ◽

Mature Mirnas ◽

Floral Transition ◽

Shoot Meristem ◽

Gene Regulatory

MicroRNAs (miRNAs) play important roles in regulating flowering and reproduction of angiosperms. Mature miRNAs are encoded by multiple MIRNA genes that can differ in their spatiotemporal activities and their contributions to gene regulatory networks, but the functions of individual MIRNA genes are poorly defined. We functionally analyzed the activity of all 5 Arabidopsis thaliana MIR172 genes, which encode miR172 and promote the floral transition by inhibiting the accumulation of APETALA2 (AP2) and APETALA2-LIKE (AP2-LIKE) transcription factors (TFs). Through genome editing and detailed confocal microscopy, we show that the activity of miR172 at the shoot apex is encoded by 3 MIR172 genes, is critical for floral transition of the shoot meristem under noninductive photoperiods, and reduces accumulation of AP2 and TARGET OF EAT2 (TOE2), an AP2-LIKE TF, at the shoot meristem. Utilizing the genetic resources generated here, we show that the promotion of flowering by miR172 is enhanced by the MADS-domain TF FRUITFULL, which may facilitate long-term silencing of AP2-LIKE transcription, and that their activities are partially coordinated by the TF SQUAMOSA PROMOTER-BINDING-LIKE PROTEIN 15. Thus, we present a genetic framework for the depletion of AP2 and AP2-LIKE TFs at the shoot apex during floral transition and demonstrate that this plays a central role in floral induction.

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Structural Maintenance of Chromosomes 5/6 Complex Is Necessary for Tetraploid Genome Stability in Arabidopsis thaliana

Frontiers in Plant Science ◽

10.3389/fpls.2021.748252 ◽

2021 ◽

Vol 12 ◽

Author(s):

Fen Yang ◽

Nadia Fernández Jiménez ◽

Joanna Majka ◽

Mónica Pradillo ◽

Ales Pecinka

Keyword(s):

Arabidopsis Thaliana ◽

Genome Stability ◽

Flowering Plants ◽

Common Phenomenon ◽

Loss Of Function ◽

Homologous Chromosomes ◽

Maternal Genome ◽

Important Player ◽

Polyploid Genome ◽

Structural Maintenance Of Chromosomes

Polyploidization is a common phenomenon in the evolution of flowering plants. However, only a few genes controlling polyploid genome stability, fitness, and reproductive success are known. Here, we studied the effects of loss-of-function mutations in NSE2 and NSE4A subunits of the Structural Maintenance of Chromosomes 5/6 (SMC5/6) complex in autotetraploid Arabidopsis thaliana plants. The diploid nse2 and nse4a plants show partially reduced fertility and produce about 10% triploid offspring with two paternal and one maternal genome copies. In contrast, the autotetraploid nse2 and nse4a plants were almost sterile and produced hexaploid and aneuploid progeny with the extra genome copies or chromosomes coming from both parents. In addition, tetraploid mutants had more severe meiotic defects, possibly due to the presence of four homologous chromosomes instead of two. Overall, our study suggests that the SMC5/6 complex is an important player in the maintenance of tetraploid genome stability and that autotetraploid Arabidopsis plants have a generally higher frequency of but also higher tolerance for aneuploidy compared to diploids.

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