Symmetric Development: Transcriptional Regulation of Symmetry Transition in Plants

SummarySymmetry breaking and re-establishment is an important developmental process that occurs during the development of multicellular organisms. A new report determines that transcription factors regulate a symmetry transition event in plants by modifying the direction of auxin transport. This provides one of the first mechanistic descriptions of a transition from bilateral to radial symmetry in plants

Nitrate-Rich Beetroot Juice Selectively Lowers Ambulatory Pressures and LDL Cholesterol in Uncontrolled but not Controlled Hypertension: a Pilot Study.

Background Dietary nitrate has been shown to increase nitrate/nitrite levels in multiple populations, with potential blood pressure lowering effects. However, there are few reports among hypertensives. Aims We aimed to assess the effect of daily nitrate in subject with controlled hypertension vs. uncontrolled hypertension. Methods On day 0, hypertensives wore an ambulatory BP monitor (ABPM) for 24h and fasting blood was taken. Subjects then consumed concentrated beetroot juice (12.9mmol nitrate) for 14 consecutive days. On day 14 subjects consumed their last nitrate dose after fasting blood was drawn and again had an ABPM for 24h. Results According to baseline ABPM, 11 subjects had controlled BP while 8 had uncontrolled BP. There were similar, significant increases in serum nitrate/nitrite in both groups. We observed little change in BP variables among controlled hypertensives. However, there were reductions in BP variables in uncontrolled hypertensives where decreases in nighttime DBP (-6 ± 4.8mmHg), arterial stiffness (-0.08 ± 0.03 ambulatory arterial stiffness index) and LDL (-0.36 ± 0.42mmol/L) reached significance (p=003, 0.05 and 0.046 respectively). Conclusions Our results support the existing data suggesting an anti-hypertensive effect of nitratecontaining beetroot juice, but only among those with uncontrolled hypertension

Dietary Nitrate in Decreased Blood Pressure in Obstructive Sleep Apnoea Syndrome: a Series of N-of-1trials

Obstructive sleep apnoea syndrome (OSAS) is a consequence of repetitive oropharyngeal airway narrowing/closure during sleep resulting in chronic intermittent hypoxaemia [1]. OSAS is regarded as an independent risk factor for hypertension (HTN) development [2] and is associated with decreased cerebral blood flow [3], leading to daytime neuropsychological sequelae [1]. Blood pressure (BP) follows a circadian rhythm termed dipping and the absence of nocturnal BP dipping is associated with target-organ damage, cerebrovascular disease, myocardial remodelling and increased cardiovascular events/mortality [4]. Abnormal BP in OSAS typically manifests as reduced nocturnal BP dipping [5]. Although continuous positive airway pressure therapy (CPAP) represents the current gold standard treatment of OSAS, its antihyper- tensive effect is limite

A streamlined method for systematic, high resolution in situ analysis of mRNA distribution in plants

BACKGROUND: In situ hybridisation can provide cellular, and in some cases sub-cellular, resolution of mRNA levels within multicellular organisms and is widely used to provide spatial and temporal information on gene expression. However, standard protocols are complex and laborious to implement, restricting analysis to one or a few genes at any one time. Whole-mount and reverse transcriptase-PCR (RT-PCR) based protocols increase throughput, but can compromise both specificity and resolution. With the advent of genome-wide analysis of gene expression, there is an urgent need to develop high-throughput in situ methods that also provide high resolution. RESULTS: Here we describe the development of a method for performing high-throughput in situ hybridisations that retains both the high resolution and the specificity of the best manual versions. This refined semi-automated protocol has the potential for determining the spatial and temporal expression patterns of hundreds of genes in parallel on a variety of tissues. We show how tissue sections can be organized on microscope slides in a manner that allows the screening of multiple probes on each slide. Slide handling, hybridisation and processing steps have been streamlined providing a capacity of at least 200 probes per week (depending on the tissue type). The technique can be applied easily to different species and tissue types, and we illustrate this with wheat seed and Arabidopsis floral meristems, siliques and seedlings. CONCLUSION: The approach has the high specificity and high resolution of previous in situ methods while allowing for the analysis of several genes expression patterns in parallel. This method has the potential to provide an analysis of gene expression patterns at the genome level

MpFEW RHIZOIDS1 miRNA-mediated lateral inhibition controls rhizoid cell patterning in Marchantia polymorpha

Lateral inhibition patterns differentiated cell types among equivalent cells during development in bacteria, metazoans, and plants. Tip-growing rhizoid cells develop among flat epidermal cells in the epidermis of the early-diverging land plant Marchantia polymorpha. We show that the majority of rhizoid cells develop individually, but some develop in linear, one-dimensional groups (chains) of between 2 and 7 rhizoid cells in wild-type plants. The distribution of rhizoid cells can be accounted for within a simple cellular automata model of lateral inhibition. The model predicted that in the absence of lateral inhibition, two-dimensional rhizoid cell groups (clusters) form. These can be larger than those formed with lateral inhibition. M. polymorpha rhizoid differentiation is positively regulated by the ROOT HAIR DEFECTIVE SIX-LIKE1 (MpRSL1) basic-helix-loop-helix (bHLH) transcription factor, which is directly repressed by the FEW RHIZOIDS1 (MpFRH1) microRNA (miRNA). To test if MpFRH1 miRNA acts during lateral inhibition, we generated loss-of-function (lof) mutants without the MpFRH1 miRNA. Two-dimensional clusters of rhizoids develop in Mpfrh1lof mutants as predicted by the model for plants that lack lateral inhibition. Furthermore, two-dimensional clusters of up to 9 rhizoid cells developed in the Mpfrh1lof mutants compared to a maximum number of 7 observed in wild-type groups. The higher steady-state levels of MpRSL1 mRNA in Mpfrh1lof mutants indicate that MpFRH1-mediated lateral inhibition involves the repression of MpRSL1 activity. Together, the modeling and genetic data indicate that MpFRH1 miRNA mediates lateral inhibition by repressing MpRSL1 during pattern formation in the M. polymorpha epidermis

An evidence-based 3D reconstruction of Asteroxylon mackiei, the most complex plant preserved from the Rhynie chert.

Funder: Biotechnology and Biological Sciences Research CouncilThe Early Devonian Rhynie chert preserves the earliest terrestrial ecosystem and informs our understanding of early life on land. However, our knowledge of the 3D structure, and development of these plants is still rudimentary. Here we used digital 3D reconstruction techniques to produce the first well-evidenced reconstruction of the structure and development of the rooting system of the lycopsid Asteroxylon mackiei, the most complex plant in the Rhynie chert. The reconstruction reveals the organisation of the three distinct axis types - leafy shoot axes, root-bearing axes, and rooting axes - in the body plan. Combining this reconstruction with developmental data from fossilised meristems, we demonstrate that the A. mackiei rooting axis - a transitional lycophyte organ between the rootless ancestral state and true roots - developed from root-bearing axes by anisotomous dichotomy. Our discovery demonstrates how this unique organ developed and highlights the value of evidence-based reconstructions for understanding the development and evolution of the first complex vascular plants on Earth

Multiple origins of dichotomous and lateral branching during root evolution

Roots of extant vascular plants proliferate through lateral branching (euphyllophytes) or dichotomy (lycophytes)1,2,3,4. The origin of these distinct modes of branching was key for plant evolution because they enabled the development of structurally and functionally different root systems that supported a diversity of shoot systems3,4,5,6. It has been unclear when lateral branching originated and how many times it evolved4,7,8. Here, we report that many euphyllophytes that were extant during the Devonian and Carboniferous periods developed dichotomous roots. Our data indicate that dichotomous root branching evolved in both lycophytes and euphyllophytes. Lateral roots then evolved at different times in three major lineages of extant euphyllophytes—the lignophytes, ferns and horsetails. The multiple origins of dichotomous and lateral root branching are extreme cases of convergent evolution that occurred during the Devonian and Carboniferous periods when the land-plant flora underwent a radiation in morphological diversity

RSL Class I Genes Controlled the Development of Epidermal Structures in the Common Ancestor of Land Plants

SummaryThe colonization of the land by plants, sometime before 470 million years ago, was accompanied by the evolution tissue systems [1–3]. Specialized structures with diverse functions—from nutrient acquisition to reproduction—derived from single cells in the outermost layer (epidermis) were important sources of morphological innovation at this time [2, 4, 5]. In extant plants, these structures may be unicellular extensions, such as root hairs or rhizoids [6–9], or multicellular structures, such as asexual propagules or secretory hairs (papillae) [10–12]. Here, we show that a ROOTHAIR DEFECTIVE SIX-LIKE (RSL) class I basic helix-loop-helix transcription factor positively regulates the development of the unicellular and multicellular structures that develop from individual cells that expand out of the epidermal plane of the liverwort Marchantia polymorpha; mutants that lack MpRSL1 function do not develop rhizoids, slime papillae, mucilage papillae, or gemmae. Furthermore, we discovered that RSL class I genes are also required for the development of multicellular axillary hairs on the gametophyte of the moss Physcomitrella patens. Because class I RSL proteins also control the development of rhizoids in mosses and root hairs in angiosperms [13, 14], these data demonstrate that the function of RSL class I genes was to control the development of structures derived from single epidermal cells in the common ancestor of the land plants. Class I RSL genes therefore controlled the generation of adaptive morphological diversity as plants colonized the land from the water

A Transcriptome Atlas of Physcomitrella patens Provides Insights into the Evolution and Development of Land Plants

Post-print version of the article.Identifying the genetic mechanisms that underpin the evolution of new organ and tissue systems is an aim of evolutionary developmental biology. Comparative functional genetic studies between angiosperms and bryophytes can define those genetic changes that were responsible for developmental innovations. Here, we report the generation of a transcriptome atlas covering most phases in the life cycle of the model bryophyte Physcomitrella patens, including detailed sporophyte developmental progression. We identified a comprehensive set of sporophyte-specific transcription factors, and found that many of these genes have homologs in angiosperms that function in developmental processes such as flowering and shoot branching. Deletion of the PpTCP5 transcription factor results in development of supernumerary sporangia attached to a single seta, suggesting that it negatively regulates branching in the moss sporophyte. Given that TCP genes repress branching in angiosperms, we suggest that this activity is ancient. Finally, comparison of P. patens and Arabidopsis thaliana transcriptomes led us to the identification of a conserved core of transcription factors expressed in tip-growing cells. We identified modifications in the expression patterns of these genes that could account for developmental differences between P. patens tip-growing cells and A. thaliana pollen tubes and root hairs.ERA-NET: (2nd call ERA-NET for Coordinating Plant Sciences); Fundação para a Ciência e a Tecnologia