Dataset Information

Unique and Conserved Features of the Barley Root Meristem.

ABSTRACT: Plant root growth is enabled by root meristems that harbor the stem cell niches as a source of progenitors for the different root tissues. Understanding the root development of diverse plant species is important to be able to control root growth in order to gain better performances of crop plants. In this study, we analyzed the root meristem of the fourth most abundant crop plant, barley (Hordeum vulgare). Cell division studies revealed that the barley stem cell niche comprises a Quiescent Center (QC) of around 30 cells with low mitotic activity. The surrounding stem cells contribute to root growth through the production of new cells that are displaced from the meristem, elongate and differentiate into specialized root tissues. The distal stem cells produce the root cap and lateral root cap cells, while cells lateral to the QC generate the epidermis, as it is typical for monocots. Endodermis and inner cortex are derived from one common initial lateral to the QC, while the outer cortex cell layers are derived from a distinct stem cell. In rice and Arabidopsis, meristem homeostasis is achieved through feedback signaling from differentiated cells involving peptides of the CLE family. Application of synthetic CLE40 orthologous peptide from barley promotes meristem cell differentiation, similar to rice and Arabidopsis. However, in contrast to Arabidopsis, the columella stem cells do not respond to the CLE40 peptide, indicating that distinct mechanisms control columella cell fate in monocot and dicot plants.

SUBMITTER: Kirschner GK

PROVIDER: S-EPMC5519606 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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Unique and Conserved Features of the Barley Root Meristem.

Kirschner Gwendolyn K GK Stahl Yvonne Y Von Korff Maria M Simon Rüdiger R

Frontiers in plant science 20170721

Plant root growth is enabled by root meristems that harbor the stem cell niches as a source of progenitors for the different root tissues. Understanding the root development of diverse plant species is important to be able to control root growth in order to gain better performances of crop plants. In this study, we analyzed the root meristem of the fourth most abundant crop plant, barley (<i>Hordeum vulgare</i>). Cell division studies revealed that the barley stem cell niche comprises a Quiescen ...[more]

PMID: 28785269

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Project description:Aluminum (Al) toxicity is considered to be the most harmful abiotic stress in acidic soils that today comprise more than 50% of the world's arable lands. Barley belongs to a group of crops that are most sensitive to Al in low pH soils. We present the RNA-seq analysis of root meristems of barley seedlings grown in hydroponics at optimal pH (6.0), low pH (4.0), and low pH with Al (10 μM of bioavailable Al3+ ions). Two independent experiments were conducted: with short-term (24 h) and long-term (7 days) Al treatment. In the short-term experiment, more genes were differentially expressed (DEGs) between root meristems grown at pH = 6.0 and pH = 4.0, than between those grown at pH = 4.0 with and without Al treatment. The genes upregulated by low pH were associated mainly with response to oxidative stress, cell wall organization, and iron ion binding. Among genes upregulated by Al, overrepresented were those related to response to stress condition and calcium ion binding. In the long-term experiment, the number of DEGs between hydroponics at pH = 4.0 and 6.0 were lower than in the short-term experiment, which suggests that plants partially adapted to the low pH. Interestingly, 7 days Al treatment caused massive changes in the transcriptome profile. Over 4,000 genes were upregulated and almost 2,000 genes were downregulated by long-term Al stress. These DEGs were related to stress response, cell wall development and metal ion transport. Based on our results we can assume that both, Al3+ ions and low pH are harmful to barley plants. Additionally, we phenotyped the root system of barley seedlings grown in the same hydroponic conditions for 7 days at pH = 6.0, pH = 4.0, and pH = 4.0 with Al. The results correspond to transcriptomic data and show that low pH itself is a stress factor that causes a significant reduction of root growth and the addition of aluminum further increases this reduction. It should be noted that in acidic arable lands, plants are exposed simultaneously to both of these stresses. The presented transcriptome analysis may help to find potential targets for breeding barley plants that are more tolerant to such conditions.

Project description:Aluminum (Al) is the most common metal in the Earth’s crust and Al toxicity is considered to be the most harmful abiotic stress in acidic soils that today comprise more than 50% of the world’s arable lands. The first symptom of Al toxicity is the reduction of root growth, resulting in decreased water and nutrients uptake, plant growth retardation, and finally, yield reduction. Barley (Hordeum vulgare L.), which is the fourth cereal crop in regards to cultivation area and production tonnage, belongs to crops most sensitive to toxic aluminum ions in low pH soils. We present the RNA-seq transcriptome analysis of root meristems of barley seedlings grown in hydroponics at optimal pH (6.0), low pH (4.0), and low pH with Al (10 µM of bioavailable Al3+ ions). Two independent experiments were conducted: with short-term (24 h) and long-term (7 days) Al treatment. Interestingly, in the short-term experiment, more genes were differentially expressed between root meristems grown at pH=6.0 and pH=4.0, than between those grown at pH=4.0 with and without Al treatment. The upregulated genes that were overrepresented at conditions of low pH, compared to optimal pH, were associated with response to oxidative stress, cell wall organization, and iron ion binding. Among genes downregulated by low pH were mainly those related to chromatin organization. These results show that low pH itself is a severe stress for barley plants. Among genes upregulated by short Al treatment, overrepresented were those related to response to stress condition and calcium ion binding. After 7 days of hydroponics, the number of DEGs between hydroponics at pH=4.0 and 6.0 were still high but lower than in the short-term experiment, which suggests that plants partially adapted to the low pH. Interestingly, 7 day Al treatment caused massive changes in the transcriptome profile compared to the condition of low pH alone. Over 4 000 genes were upregulated and almost 2 000 genes were downregulated by long-term Al stress. These DEGs were related to e.g. stress response, cell wall development and metal ion transport. Based on our results we can assume that both, Al3+ ions and low pH are harmful to barley plants.Additionally, we phenotyped in detail the root system of barley seedlings grown in the same hydroponic conditions for 7 days at pH=6.0, pH=4.0, and pH=4.0 with Al. The results correspond to transcriptomic data and show that low pH itself is a stress facor that causes a significant reduction of root growth and the addition of aluminum further increases this reduction. It should be underlined that in the acidic arable lands, plants are exposed simultaneously to both of these stresses (low pH and Al), as Al becomes soluble at pH below 5.5. The presented transcriptome analysis may help to find potential targets for breeding barley plants more tolerant to such conditions.

Project description:BACKGROUND: Plant genomes contain a high proportion of duplicated genes as a result of numerous whole, segmental and local duplications. These duplications lead up to the formation of gene families, which are the usual material for many evolutionary studies. However, all characterized genomes include single-copy (unique) genes that have not received much attention. Unlike gene duplication, gene loss is not an unspecific mechanism but is rather influenced by a functional selection. In this context, we have established and used stringent criteria in order to identify suitable sets of unique genes present in plant proteomes. Comparisons of unique genes in the green phylum were used to characterize the gene and protein features exhibited by both conserved and species-specific unique genes. RESULTS: We identified the unique genes within both A. thaliana and O. sativa genomes and classified them according to the number of homologs in the alternative species: none (U{1:0}), one (U{1:1}) or several (U{1:m}). Regardless of the species, all the genes in these groups present some conserved characteristics, such as small average protein size and abnormal intron number. In order to understand the origin and function of unique genes, we further characterized the U{1:1} gene pairs. The possible involvement of sequence convergence in the creation of U{1:1} pairs was discarded due to the frequent conservation of intron positions. Furthermore, an orthology relationship between the two members of each U{1:1} pair was strongly supported by a high conservation in the protein sizes and transcription levels. Within the promoter of the unique conserved genes, we found a number of TATA and TELO boxes that specifically differed from their mean number in the whole genome. Many unique genes have been conserved as unique through evolution from the green alga Ostreococcus lucimarinus to higher plants. Plant unique genes may also have homologs in bacteria and we showed a link between the targeting towards plastids of proteins encoded by plant nuclear unique genes and their homology with a bacterial protein. CONCLUSION: Many of the A. thaliana and O. sativa unique genes are conserved in plants for which the ancestor diverged at least 725 million years ago (MYA). Half of these genes are also present in other eukaryotic and/or prokaryotic species. Thus, our results indicate that (i) a strong negative selection pressure has conserved a number of genes as unique in genomes throughout evolution, (ii) most unique genes are subjected to a low divergence rate, (iii) they have some features observed in housekeeping genes but for most of them there is no functional annotation and (iv) they may have an ancient origin involving a possible gene transfer from ancestral chloroplasts or bacteria to the plant nucleus.

Dataset Information

Unique and Conserved Features of the Barley Root Meristem.

Publications

Unique and Conserved Features of the Barley Root Meristem.

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