Age-associated growth control modifies leaf proximodistal symmetry and enabled leaf shape diversification.

Biological shape diversity is often manifested in modulation of organ symmetry and modification of the patterned elaboration of repeated shape elements. Whether and how these two aspects of shape determination are coordinately regulated is unclear. Plant leaves provide an attractive system to investigate this problem, because they often show asymmetries along the proximodistal (PD) axis of their blades, along which they can also produce repeated marginal outgrowths such as serrations or leaflets.

Cell-cycle-linked growth reprogramming encodes developmental time into leaf morphogenesis.

How is time encoded into organ growth and morphogenesis? We address this question by investigating heteroblasty, where leaf development and form are modified with progressing plant age. By combining morphometric analyses, fate-mapping through live-imaging, computational analyses, and genetics, we identify age-dependent changes in cell-cycle-associated growth and histogenesis that underpin leaf heteroblasty. We show that in juvenile leaves, cell proliferation competence is rapidly released in a "proliferation burst" coupled with fast growth, whereas in adult leaves, proliferative growth is sustained for longer and at a slower rate.

Cytokinin promotes growth cessation in the Arabidopsis root.

The Arabidopsis root offers good opportunities to investigate how regulated cellular growth shapes different tissues and organs, a key question in developmental biology. Along the root's longitudinal axis, cells sequentially occupy different developmental states. Proliferative meristematic cells give rise to differentiating cells, which rapidly elongate in the elongation zone, then mature and stop growing in the differentiation zone.

The Copper-microRNA Pathway Is Integrated with Developmental and Environmental Stress Responses in .

As an essential nutrient, copper (Cu) scarcity causes a decrease in agricultural production. Cu deficiency responses include the induction of several microRNAs, known as Cu-miRNAs, which are responsible for degrading mRNAs from abundant and dispensable cuproproteins to economize copper when scarce. Cu-miRNAs, such as miR398 and miR408 are conserved, as well as the signal transduction pathway to induce them under Cu deficiency.

A WOX/Auxin Biosynthesis Module Controls Growth to Shape Leaf Form.

A key challenge in biology is to understand how the regional control of cell growth gives rise to final organ forms. Plant leaves must coordinate growth along both the proximodistal and mediolateral axes to produce their final shape. However, the cell-level mechanisms controlling this coordination remain largely unclear.

CRISPR/Cas9-Mediated Mutagenesis of in .

The small crucifer bears complex leaves divided into leaflets. This is in contrast to its relative, the reference plant , which has simple leaves. Comparative studies between these species provide attractive opportunities to study the diversification of form.

Autoregulation of RCO by Low-Affinity Binding Modulates Cytokinin Action and Shapes Leaf Diversity.

Mechanisms through which the evolution of gene regulation causes morphological diversity are largely unclear. The tremendous shape variation among plant leaves offers attractive opportunities to address this question. In cruciferous plants, the REDUCED COMPLEXITY (RCO) homeodomain protein evolved via gene duplication and acquired a novel expression domain that contributed to leaf shape diversity.

A Growth-Based Framework for Leaf Shape Development and Diversity.

How do genes modify cellular growth to create morphological diversity? We study this problem in two related plants with differently shaped leaves: Arabidopsis thaliana (simple leaf shape) and Cardamine hirsuta (complex shape with leaflets). We use live imaging, modeling, and genetics to deconstruct these organ-level differences into their cell-level constituents: growth amount, direction, and differentiation. We show that leaf shape depends on the interplay of two growth modes: a conserved organ-wide growth mode that reflects differentiation; and a local, directional mode that involves the patterning of growth foci along the leaf edge.

LMI1 homeodomain protein regulates organ proportions by spatial modulation of endoreduplication.

How the interplay between cell- and tissue-level processes produces correctly proportioned organs is a key problem in biology. In plants, the relative size of leaves compared with their lateral appendages, called stipules, varies tremendously throughout development and evolution, yet relevant mechanisms remain unknown. Here we use genetics, live imaging, and modeling to show that in leaves the LATE MERISTEM IDENTITY1 (LMI1) homeodomain protein regulates stipule proportions via an endoreduplication-dependent trade-off that limits tissue size despite increasing cell growth.

The Cardamine hirsuta genome offers insight into the evolution of morphological diversity.

Finding causal relationships between genotypic and phenotypic variation is a key focus of evolutionary biology, human genetics and plant breeding. To identify genome-wide patterns underlying trait diversity, we assembled a high-quality reference genome of Cardamine hirsuta, a close relative of the model plant Arabidopsis thaliana. We combined comparative genome and transcriptome analyses with the experimental tools available in C.

Daily rhythmicity of high affinity copper transport.

A differential demand for copper (Cu) of essential cupro-proteins that act within the mitochondrial and chloroplastal electronic transport chains occurs along the daily light/dark cycles. This requires a fine-tuned spatiotemporal regulation of Cu delivery, becoming especially relevant under non-optimal growth conditions. When scarce, Cu is imported through plasma membrane-bound high affinity Cu transporters (COPTs) whose coding genes are transcriptionally induced by the SPL7 transcription factor.

Alternate wiring of a KNOXI genetic network underlies differences in leaf development of A. thaliana and C. hirsuta.

Two interrelated problems in biology are understanding the regulatory logic and predictability of morphological evolution. Here, we studied these problems by comparing Arabidopsis thaliana, which has simple leaves, and its relative, Cardamine hirsuta, which has dissected leaves comprising leaflets. By transferring genes between the two species, we provide evidence for an inverse relationship between the pleiotropy of SHOOTMERISTEMLESS (STM) and BREVIPEDICELLUS (BP) homeobox genes and their ability to modify leaf form.

Modulation of copper deficiency responses by diurnal and circadian rhythms in Arabidopsis thaliana.

Copper homeostasis under deficiency is regulated by the SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7 (SPL7) transcription factor. The daily oscillating expression of two SPL7-dependent copper deficiency markers, COPPER TRANSPORTER (COPT2) and IRON SUPEROXIDE DISMUTASE (FSD1), has been followed by quantitative PCR and in promoter:LUCIFERASE transgenic plants. Both genes showed circadian and diurnal regulation.

Heterochrony underpins natural variation in Cardamine hirsuta leaf form.

A key problem in biology is whether the same processes underlie morphological variation between and within species. Here, by using plant leaves as an example, we show that the causes of diversity at these two evolutionary scales can be divergent. Some species like the model plant Arabidopsis thaliana have simple leaves, whereas others like the A.

Functional characterisation of Arabidopsis SPL7 conserved protein domains suggests novel regulatory mechanisms in the Cu deficiency response.

Background: The Arabidopsis SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE (SPL) transcription factor SPL7 reprograms cellular gene expression to adapt plant growth and cellular metabolism to copper (Cu) limited culture conditions. Plant cells require Cu to maintain essential processes, such as photosynthesis, scavenging reactive oxygen species, cell wall lignification and hormone sensing. More specifically, SPL7 activity promotes a high-affinity Cu-uptake system and optimizes Cu (re-)distribution to essential Cu-proteins by means of specific miRNAs targeting mRNA transcripts for those dispensable.

The Arabidopsis KIN17 and its homolog KLP mediate different aspects of plant growth and development.

Proteins harboring the kin17 domain (KIN17) constitute a family of well-conserved eukaryotic nuclear proteins involved in nucleic acid metabolism. In mammals, KIN17 orthologs contribute to DNA replication, RNA splicing, and DNA integrity maintenance. Recently, we reported a functional characterization of an Arabidopsis thaliana KIN17 homolog (AtKIN17) that uncovered a role for this protein in tuning physiological responses during copper (Cu) deficiency and oxidative stress.

Leaf shape evolution through duplication, regulatory diversification, and loss of a homeobox gene.

In this work, we investigate morphological differences between Arabidopsis thaliana, which has simple leaves, and its relative Cardamine hirsuta, which has dissected leaves comprising distinct leaflets. With the use of genetics, interspecific gene transfers, and time-lapse imaging, we show that leaflet development requires the REDUCED COMPLEXITY (RCO) homeodomain protein. RCO functions specifically in leaves, where it sculpts developing leaflets by repressing growth at their flanks.

A conserved KIN17 curved DNA-binding domain protein assembles with SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE7 to adapt Arabidopsis growth and development to limiting copper availability.

Proper copper (Cu) homeostasis is required by living organisms to maintain essential cellular functions. In the model plant Arabidopsis (Arabidopsis thaliana), the SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE7 (SPL7) transcription factor participates in reprogramming global gene expression during Cu insufficiency in order to improve the metal uptake and prioritize its distribution to Cu proteins of major importance. As a consequence, spl7 null mutants show morphological and physiological disorders during Cu-limited growth, resulting in lower fresh weight, reduced root elongation, and chlorosis.

The Arabidopsis COPT6 transport protein functions in copper distribution under copper-deficient conditions.

Copper (Cu), an essential redox active cofactor, participates in fundamental biological processes, but it becomes highly cytotoxic when present in excess. Therefore, living organisms have established suitable mechanisms to balance cellular and systemic Cu levels. An important strategy to maintain Cu homeostasis consists of regulating uptake and mobilization via the conserved family of CTR/COPT Cu transport proteins.

SPL8 and miR156-targeted SPL genes redundantly regulate Arabidopsis gynoecium differential patterning.

SPL8 and miR156-targeted SPL genes are known to play an essential role in Arabidopsis anther development. Here we show that these SPL genes are also expressed within the developing gynoecium, where they redundantly control development of the female reproductive tract. Whereas the gynoecium morphology in the spl8 single mutant is largely normal, additional down-regulation of miR156-targeted SPL genes results in a shortened style and an apically swollen ovary narrowing onto an elongated gynophore.

Novel positive regulatory role for the SPL6 transcription factor in the N TIR-NB-LRR receptor-mediated plant innate immunity.

Following the recognition of pathogen-encoded effectors, plant TIR-NB-LRR immune receptors induce defense signaling by a largely unknown mechanism. We identify a novel and conserved role for the SQUAMOSA PROMOTER BINDING PROTEIN (SBP)-domain transcription factor SPL6 in enabling the activation of the defense transcriptome following its association with a nuclear-localized immune receptor. During an active immune response, the Nicotiana TIR-NB-LRR N immune receptor associates with NbSPL6 within distinct nuclear compartments.

SPL8 Acts Together with the Brassinosteroid-Signaling Component BIM1 in Controlling Arabidopsis thaliana Male Fertility.

The non-miR156 targeted SBP-box gene SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 8 (SPL8), plays an important role in Arabidopsis anther development, where its loss-of-function results in a semi-sterile phenotype. Fully male-sterile plants are obtained when a spl8 loss-of-function mutation is introduced into a 35S:MIR156 genetic background, thereby revealing functional redundancy between SPL8 and miR156-targeted SBP-box genes. Here, we show that BIM1, a gene encoding a bHLH protein involved in brassinosteroid signaling and embryonic patterning, functions redundantly with SPL8 in its requirement for male fertility.