HAWAIIAN SKIRT, and F-box gene from Arabidopsis, is a new player in the microRNA pathway

F-box proteins belong to a multi-protein E3 ubiquitin ligase complex (SCF) that target proteins for degradation via the proteasome.We demonstrated that HAWAIIAN SKIRT(HWS), an Arabidopsis ubiquitin protein ligase (SCFHWS), regulates organ growth, flower development and timing of abscission. Mutants of this gene (hws-1) are pleiotropic and the most obvious phenotype is the fusion of its floral organs, a phenotype shared with the cuc1/cuc2 double mutants and over-expressing lines of MIR164B. To understand the molecular mechanisms of HWS during plant development, an ethylmethylsulphonate mutagenized population of hws-1 seeds was generated and screened for mutations suppressing the hws-1 sepal fusion. We isolated shs-1/hws-1, shs-2/hws-1, and shs-3/hws-1, (suppressor of hws-1) mutants. Mapping analyses shown that shs1 is mutated in the miRNA164 binding site of CUPSHAPED COTYLEDON1 (CUC1) mRNA; while shs-2 and shs-3 are novel alleles of the plant homolog of Exporting-5 HASTY (HST), known to be important in miRNA biogenesis, function and transport. Consequently, we renamed them cuc1-1D, hst23 and hst24, respectively. We demonstrated that transcript levels of CUC1 and CUPSHAPED COTYLEDON 2 (CUC2), and MIR164 change in cuc1-1D and in hws-1 mutants; analyses revealed a role for HWS in cell proliferation and control of floral organ number. Additional genetic crosses between hws-1 and mutant lines for genes in the miRNA pathway were performed and double mutants obtained shown restoration of the hws-1 sepal fusion phenotype. Our data propose HWS as a new regulator in miRNA pathway and reveal a role for HWS to control floral organ number and cell proliferation

HAWAIIAN SKIRT controls size and floral organ number by modulating CUC1 and CUC2 expression

The Arabidopsis thaliana F-box gene HAWAIIAN SKIRT (HWS) affects organ growth and the timing of floral organ abscission. The loss-of-function hws-1 mutant exhibits fused sepals and increased organ size. To understand the molecular mechanisms of HWS during plant development, we mutagenized hws-1 seeds with ethylmethylsulphonate (EMS) and screened for mutations suppressing hws-1 associated phenotypes. We isolated the shs1/hws-1 (suppressor of hws-1) mutant in which hws-1 sepal fusion phenotype was suppressed. The shs1/hws-1 mutant carries a G→A nucleotide substitution in the MIR164 binding site of CUP-SHAPED COTYLEDON 1 (CUC1) mRNA. CUC1 and CUP-SHAPED COTYLEDON 2 (CUC2) transcript levels were altered in shs1, renamed cuc1-1D, and in hws-1 mutant. Genetic interaction analyses using single, double and triple mutants of cuc1-1D, cuc2-1D (a CUC2 mutant similar to cuc1-1D), and hws-1, demonstrate that HWS, CUC1 and CUC2 act together to control floral organ number. Loss of function of HWS is associated with larger petal size due to alterations in cell proliferation and mitotic growth, a role shared with the CUC1 gene

The Arabidopsis thaliana F-box gene HAWAIIAN SKIRT is a new player in the microRNA pathway

In Arabidopsis, the F-box HAWAIIAN SKIRT (HWS) protein is important for organ growth. Loss of function of HWS exhibits pleiotropic phenotypes including sepal fusion. To dissect the HWS role, we EMS-mutagenized hws-1 seeds and screened for mutations that suppress hws-1 associated phenotypes. We identified shs-2 and shs-3 (suppressor of hws-2 and 3) mutants in which the sepal fusion phenotype of hws-1 was suppressed. shs-2 and shs-3 (renamed hst-23/hws-1 and hst-24/hws-1) carry transition mutations that result in premature terminations in the plant homolog of Exportin-5 HASTY (HST), known to be important in miRNA biogenesis, function and transport. Genetic crosses between hws-1 and mutant lines for genes in the miRNA pathway, also suppress the phenotypes associated with HWS loss of function, corroborating epistatic relations between the miRNA pathway genes and HWS. In agreement with these data, accumulation of miRNA is modified in HWS loss or gain of function mutants. Our data propose HWS as a new player in the miRNA pathway, important for plant growth

Rose genomics: challenges and perspectives

International audienceCultivated roses have a very ancient history. Artificial crossing led to what is today perceived as modern rose cultivars. Impressively, these modern rose cultivars were established from less than 10 species, which have contributed to the origin of the about 35,000 existing rose cultivars. Roses exhibit an extraordinary diversity of traits, both of economic and scientific importance. Several recent studies have been marked as important milestones on the journey towards deeply understanding the molecular and genetic mechanisms that govern these traits, yet we still lack information on the genome sequences of rose species and cultivars, especially those that heavily participated to rose domestication and breeding programs

Single cell wall nonlinear mechanics revealed by a multiscale analysis of AFM force-indentation curves

Individual plant cells are rather complex mechanical objects. Despite the fact that their wall mechanical strength may be weakened by comparison with their original tissue template, they nevertheless retain some generic properties of the mother tissue, namely the viscoelasticity and the shape of their walls, which are driven by their internal hydrostatic turgor pressure. This viscoelastic behavior, which affects the power- law response of these cells when indented by an atomic force cantilever with a pyramidal tip, is also very sensitive to the culture media. To our knowledge, we develop here an original analyzing method, based on a multiscale decomposition of force-indentation curves, that reveals and quantifies for the first time the nonlinearity of the mechanical response of living single plant cells upon mechanical deformation. Further comparing the nonlinear strain responses of these isolated cells in three different media, we reveal an alteration of their linear bending elastic regime in both hyper- and hypotonic conditions

HAWAIIAN SKIRT, and F-box gene from Arabidopsis, is a new player in the microRNA pathway

F-box proteins belong to a multi-protein E3 ubiquitin ligase complex (SCF) that target proteins for degradation via the proteasome.We demonstrated that HAWAIIAN SKIRT(HWS), an Arabidopsis ubiquitin protein ligase (SCFHWS), regulates organ growth, flower development and timing of abscission. Mutants of this gene (hws-1) are pleiotropic and the most obvious phenotype is the fusion of its floral organs, a phenotype shared with the cuc1/cuc2 double mutants and over-expressing lines of MIR164B. To understand the molecular mechanisms of HWS during plant development, an ethylmethylsulphonate mutagenized population of hws-1 seeds was generated and screened for mutations suppressing the hws-1 sepal fusion. We isolated shs-1/hws-1, shs-2/hws-1, and shs-3/hws-1, (suppressor of hws-1) mutants. Mapping analyses shown that shs1 is mutated in the miRNA164 binding site of CUPSHAPED COTYLEDON1 (CUC1) mRNA; while shs-2 and shs-3 are novel alleles of the plant homolog of Exporting-5 HASTY (HST), known to be important in miRNA biogenesis, function and transport. Consequently, we renamed them cuc1-1D, hst23 and hst24, respectively. We demonstrated that transcript levels of CUC1 and CUPSHAPED COTYLEDON 2 (CUC2), and MIR164 change in cuc1-1D and in hws-1 mutants; analyses revealed a role for HWS in cell proliferation and control of floral organ number. Additional genetic crosses between hws-1 and mutant lines for genes in the miRNA pathway were performed and double mutants obtained shown restoration of the hws-1 sepal fusion phenotype. Our data propose HWS as a new regulator in miRNA pathway and reveal a role for HWS to control floral organ number and cell proliferation

Analysis of gene expression in rose petals using expressed sequence tags

International audienc

A Comparative Mechanical Analysis of Plant and Animal Cells Reveals Convergence across Kingdoms

International audiencePlant and animals have evolved different strategies for their development. Whether this is linked to major differences in their cell mechanics remains unclear, mainly because measurements on plant and animal cells relied on independent experiments and setups, thus hindering any direct comparison. In this study we used the same micro-rheometer to compare animal and plant single cell rheology. We found that wall-less plant cells exhibit the same weak power law rheology as animal cells, with comparable values of elastic and loss moduli. Remarkably, microtubules primarily contributed to the rheological behavior of wall-less plant cells whereas rheology of animal cells was mainly dependent on the actin network. Thus, plant and animal cells evolved different molecular strategies to reach a comparable cytoplasmic mechanical core, suggesting that evolutionary convergence could include the internal biophysical properties of cells

Phenotypic characterisation of <i>hst-24</i>.

<p>(<b>A</b>) Dissected flower from developmental stage 15a from <i>hst-24/hws-1</i>. (<b>B</b>) Comparative analyses of sepal and petal sizes from flowers (stage 15a) of Col-0, <i>hws-1</i>, <i>hst-24/hws-1</i> and <i>hst-24</i>. (<b>C</b>). Twenty-five flowers from six plants of Col-0, <i>hst-24/hws-1</i> and <i>hst-24</i> were dissected and their sepals and petals quantified and statistically analysed by regression analyses using generalized linear models. Stars indicate a significant difference in the mean at P≤0.001 n = 450. Bars indicate SD. (<b>D</b>) Rosettes, and (<b>E</b>) Dissected leaves from 22-day-old plants from Col-0, <i>hws-1</i>, <i>hst-24/hws-1</i> and <i>hst-24</i>. Bars in A, B = 1mm; and in D, E = 1 cm.</p

The <i>shs1</i> mutant is an allele of <i>CUC1</i>.

<p>(<b>A-H</b>), Aerial and (<b>I-P</b>), lateral views of flowers at stage 15a; and (<b>Q-X</b>), lateral view of mature green siliques. From: (<b>A, I, Q</b>), Columbia-0; (<b>B, J, R</b>), <i>hws-1</i> (Columbia-0 background);(<b>C, K, S</b>), <i>hws-2</i> (<i>L</i>er background); (<b>D, L, T</b>), <i>hws-1/shs</i>+/-; (E, M. U), <i>hws-1/shs1 (hws-1/cuc1-1D)</i>; and primary transformants of (<b>F, N, V</b>), Columbia-0; (<b>G, O, W</b>), <i>hws-1</i>; and (<b>H, P, X</b>), <i>hws-2</i> complemented with a genomic region containing the <i>CUC1pr</i>::<i>CUC1-1D</i> gene. Scale bars: 1mm. Arrows show the sepal fusions. A petal in F and a sepal on P have been removed. * in N shows stamen fusion. (<b>Y</b>), Mapping strategy used to identify the <i>cuc1-1D</i> mutation. Structure of the gene and location of the transition substitution (G→A) 1,238bp from the ATG are included, intragenic regions are represented by thin lines and exons by black boxes.</p