A global view of RNA-protein interactions reveals novel root hair cell fate regulators
Ontology highlight
ABSTRACT: The Arabidopsis thaliana root epidermis is comprised of two cell types, hair and nonhair cells, which differentiate from the same precursor. Although the transcriptional programs regulating these events are well studied, post-transcriptional factors functioning in this cell fate decision are mostly unknown. Here, we globally identify RNA-protein interactions and RNA secondary structure in hair and nonhair cell nuclei. This analysis reveals distinct structural and protein binding patterns across both transcriptomes, allowing identification of differential RNA binding protein (RBP) recognition sites. Using these sequences, we identify two RBPs that regulate hair cell development. Specifically, we find that SERRATE functions in a microRNA-dependent manner to inhibit hair cell fate, while also terminating hair growth in differentiated hair cells independent of microRNAs. Additionally, we show that GLYCINE-RICH PROTEIN 8 alleviates phosphate starvation stress while promoting hair cell fate. In total, this global analysis reveals novel post-transcriptional regulators of plant root epidermal cell fate.
Project description:The root epidermis of Arabidopsis provides a simple and experimentally useful model for studying the molecular basis of cell fate and differentiation. The goal of this study was to define the larger gene regulatory network that governs the differentiation of the root hair and non-hair cell types of the Arabidopsis root epidermis. Transcript levels in the root epidermis of wild-type and mutant lines were assessed by purifying populations of root epidermal cells using fluorescence-based cell-sorting. Further, the role of the plant hormones auxin and ethylene on root epidermis development was assessed by defining transcript levels in the root epidermis of plants grown on media containing IAA or ACC. These microarray results were used to construct a comprehensive gene regulatory network that depicts the transcriptional control of root epidermal cell fate and differentiation in Arabidopsis.
Project description:Root hairs are an extensive structure of root epidermal cells and are critical for nutrient acquisition, soil anchorage, and environ- mental interactions in sessile plants. The phytohormone ethylene (ET) promotes root hair growth and also mediates the effects of different signals that stimulate hair cell development. However, the molecular basis of ET-induced root hair growth remains poorly understood. Here, we show that ET-activated transcription factor ETHYLENE-INSENSITIVE 3 (EIN3) physically interacts with ROOT HAIR DEFECTIVE 6 (RHD6), a well-documented positive regulator of hair cells, and that the two factors directly coactivate the hair length-determining gene RHD6-LIKE 4 (RSL4) to promote root hair elongation. Transcriptome analysis further revealed the parallel roles of the regulator pairs EIN3/EIL1 (EIN3-LIKE 1) and RHD6/ RSL1 (RHD6-LIKE 1). EIN3/EIL1 and RHD6/RSL1 coordinately en- hance root hair initiation by selectively regulating a subset of core root hair (H) genes. Thus, our work reveals a key transcriptional complex consisting of EIN3/EIL1 and RHD6/RSL1 in the control of root hair initiation and elongation, and provides a molecular framework for the integration of environmental signals and in- trinsic regulators in modulating plant organ development.
Project description:The root epidermis of Arabidopsis provides a simple and experimentally useful model for studying the molecular basis of cell fate and differentiation. The goal of this study was to define the larger gene regulatory network that governs the differentiation of the root hair and non-hair cell types of the Arabidopsis root epidermis. Transcript levels in the root epidermis of wild-type and mutant lines were assessed by purifying populations of root epidermal cells using fluorescence-based cell-sorting. Further, the role of the plant hormones auxin and ethylene on root epidermis development was assessed by defining transcript levels in the root epidermis of plants grown on media containing IAA or ACC. These microarray results were used to construct a comprehensive gene regulatory network that depicts the transcriptional control of root epidermal cell fate and differentiation in Arabidopsis. The cells of the developing root epidermis were obtained by growing plant seedlings expressing the WER::GFP transgene under sterile conditions on MS media, cutting off root tips (including all developmental stages), protoplasting the roots, and purifying cells containing GFP using FACS. The WER::GFP transgene is expressed throughout the developing cells of the root epidermis and the lateral root cap. Three biological replicates were analyzed for each of the 25 plant lines examined in this study.
Project description:Phosphate (Pi) deficiency alters root hair length and frequency as a means of increasing the absorptive surface area of roots. Three partly redundant single R3 MYB proteins, CAPRICE (CPC), ENHANCER OF TRY AND CPC1 (ETC1) and TRIPTYCHON (TRY), positively regulate the root hair cell fate by participating in a lateral inhibition mechanism. To identify putative targets and processes that are controlled by these three transcription factors (TFs), we conducted transcriptional profiling of roots from Arabidopsis thaliana wild-type plants, and cpc, etc1 and try mutants grown under Pi-replete and Pi-deficient conditions using RNA-seq.
Project description:Cyanide is stoichiometrically produced as a co-product of the ethylene biosynthesis pathway, and it is detoxified by the b-cyanoalanine synthase enzyme. The molecular and phenotypical analysis of T-DNA insertional mutants of the mitochondrial b-cyanoalanine synthase CYS-C1 suggests that discrete accumulation of cyanide is not toxic for the plant and does not alter mitochondrial respiration rates, but does act as a strong inhibitor of root hair development. The cys-c1 null allele is defective in root hair formation and accumulates cyanide in root tissues. The root hair defect is phenocopied in wild type plants by the exogenous addition of cyanide to the growth medium and is reversed by the addition of hydroxocobalamin. Hydroxocobalamin not only recovers the root phenotype of the mutant, but also the formation of ROS at the initial step of the root hair tip. Transcriptional profile analysis of the cys-c1 mutant reveals that cyanide accumulation acts as a repressor signal for several genes encoding enzymes involved in cell wall rebuilding and the formation of the root hair tip, as well as genes involved in ethylene signaling and metabolism. Our results demonstrate that mitochondrial b-cyanoalanine synthase activity is essential to maintain a low level of cyanide for proper root hair development.
Project description:Cyanide is stoichiometrically produced as a co-product of the ethylene biosynthesis pathway, and it is detoxified by the b-cyanoalanine synthase enzyme. The molecular and phenotypical analysis of T-DNA insertional mutants of the mitochondrial b-cyanoalanine synthase CYS-C1 suggests that discrete accumulation of cyanide is not toxic for the plant and does not alter mitochondrial respiration rates, but does act as a strong inhibitor of root hair development. The cys-c1 null allele is defective in root hair formation and accumulates cyanide in root tissues. The root hair defect is phenocopied in wild type plants by the exogenous addition of cyanide to the growth medium and is reversed by the addition of hydroxocobalamin. Hydroxocobalamin not only recovers the root phenotype of the mutant, but also the formation of ROS at the initial step of the root hair tip. Transcriptional profile analysis of the cys-c1 mutant reveals that cyanide accumulation acts as a repressor signal for several genes encoding enzymes involved in cell wall rebuilding and the formation of the root hair tip, as well as genes involved in ethylene signaling and metabolism. Our results demonstrate that mitochondrial b-cyanoalanine synthase activity is essential to maintain a low level of cyanide for proper root hair development. Using Affymetrix ATH1 GeneChips, we performed a comparative transcriptomic analysis of roots of the cys-c1 and wild type plants. Total RNA was extracted from roots of 14-days-old plants grown under identical conditions on MS medium (three biological replicates for each genotype), and these samples were used to prepare complementary RNA and and analyzed using the Affymetrix-Arabidopsis ATH1GeneChip array.
Project description:We provide an atlas of gene and protein expression in Arabidopsis root hair cells, generated by paired-end RNA-seq and LC/MS-MS analysis from protoplasts that carry the root hair-specific pEXP7-GFP reporter construct. In total, transcripts from 23,234 genes were detected in root hairs; those related to cell wall biosynthesis and translation differed most dramatically in abundance when compared to non-GFP root protoplasts.
Project description:Plant root architecture is a major determinant of fitness, and is under constant modification in response to favorable and unfavorable environmental stimuli. Beyond impacts on the primary root, the environment can also alter the position, spacing, density, and length of secondary or lateral roots. Lateral root development is among the best-studied developmental processes in Arabidopsis thaliana, yet the earliest steps of organogenesis remain elusive. Among the challenges faced in capturing these early molecular events is the fact that this process occurs in a small number of cells with unpredictable timing. The advent of single-cell sequencing affords the opportunity to isolate cells undergoing this fate transition and examine their transcriptomes independently. Using this approach, we successfully captured the transcriptomes of lateral root primordia and discovered many previously unreported upregulated genes. To further study this process, we developed a method to selectively repress genes in the xylem pole pericycle cells where lateral roots originate. We found that expression of several of the upregulated genes was required for normal root development. In addition, we discovered a subpopulation of cells in the endodermal cell file that respond to lateral root initiation, further highlighting the benefits of the single cell approach.
Project description:In order to identify the possible protein targets of cyanide in the regulation of root hair, we have carried out a single cell proteomic approach to characterize the protein atlas in wild type root hair cells compared to the cas-c1 mutant cells. Root hair specific cells were obtained from isolated protoplast from root tissues of Arabidopsis wt-pCOBL9:GFP and cas-c1-pCOBL9:GFP lines. To analyze the effect of the CAS-C1 mutation, we isolated 1 x 106 root hair cells by Fluorescence-activated cell sorting (FACS) from three independent replicate of wt-pCOBL9:GFP and cas-c1-pCOBL9:GFP roots. The extracted proteins from each sample were trypsin-digested and the digested peptides were analyzed by liquid chromatography-high resolution mass spectrometry (LC-MS/MS) for protein identification. In wild type samples, we have identified 3829 unique proteins at a false discovery rate below 1% (FDR<1%), that represent almost 10% of the total Arabidopsis proteome. In protein extract of the cas-c1-pCOBL9:GFP roots samples, we have identified 3972 proteins of which 3515 were commons in both cell types, 310 were only identified y wild type and 457 only in cas-c1 mutant (Fig. 5).