Root Hair Formation Research Articles

Adaptor proteins GIR1 and GIR2. II. Interaction with the co-repressor TOPLESS and promotion of histone deacetylation of target chromatin

Understanding how root hair development is controlled is important for understanding of many fundamental aspects of plant biology. Previously, we identified two plant-specific adaptor proteins GIR1 and GIR2 that interact with the major regulator of root hair development GL2 and suppress formation of root hair. Here, we show that GIR1 and GIR2 also interact with the co-repressor TOPLESS (TPL). This interaction required the GIR1 protein EAR motif, and was essential for the transcriptional repressor activity of GIR1. Both GIR1 and GIR2 promoted histone hypoacetylation of their target chromatin. Potentially, GIR1 and GIR2 might may link TPL to and participate in epigenetic regulation of root hair development.

Adaptor proteins GIR1 and GIR2. I. Interaction with the repressor GLABRA2 and regulation of root hair development

Plants use specialized root outgrowths, termed root hairs, to enhance acquisition of nutrients and water, help secure anchorage, and facilitate interactions with soil microbiome. One of the major regulators of this process is GLABRA2 (GL2), a transcriptional repressor of root hair differentiation. However, regulation of the GL2-function is relatively well characterized, it remains completely unknown whether GL2 itself functions in complex with other transcriptional regulators. We identified GIR1 and GIR2, a plant-specific two-member family of closely related proteins that interact with GL2. Loss-of-function mutants of GIR1 and GIR2 enhanced development of root hair whereas gain-of-function mutants repressed it. Thus, GIR1 and GIR2 might function as adaptor proteins that associate with GL2 and participate in control of root hair formation.

Seed-vectored endophytic bacteria modulate development of rice seedlings.

The aim of the present study was to evaluate the effects of the removal of indigenous bacteria from rice seeds on seedling growth and development. Here we report the presence of three indigenous endophytic bacteria in rice seeds that play important roles in modulating seedling development (shoot and root lengths, and formation of root hairs and secondary roots) and defence against pathogens. Seed-associated bacteria were removed using surface sterilization with NaOCl (bleach) followed by antibiotic treatment. When bacteria were absent, growth of seedlings in terms of root hair development and overall seedling size was less than that of seedlings that contained bacteria. Reactive oxygen staining of seedlings showed that endophytic bacteria became intracellular in root parenchyma cells and root hairs. Roots containing endophytic bacteria were seen to stain densely for reactive oxygen, while roots free of bacteria stained lightly for reactive oxygen. Bacteria were isolated and identified as Enterobacter asburiae (VWB1), Pantoea dispersa (VWB2) and Pseudomonas putida (VWB3) by 16S rDNA sequencing. Bacteria were found to produce indole acetic acid (auxins), inhibited the pathogen Fusarium oxysporum and solubilized phosphate. Reinoculation of bacteria onto seedlings derived from surface-disinfected rice and Bermuda grass seeds significantly restored seedling growth and development. Rice seeds harbour indigenous bacterial endophytes that greatly influence seedling growth and development, including root and shoot lengths, root hair formation and disease susceptibility of rice seedlings. This study shows that seeds of rice naturally harbour bacterial endophytes that play key roles in modulation of seedling development.

Roles of Genotype-Determined Mycotoxins in Maize Seedling Blight Caused by Fusarium graminearum.

Fusarium graminearum is an important causal agent of maize seedling blight. The species includes several chemotypes that produce various forms of deoxynivalenol (DON) and nivalenol (NIV). To understand the effects and roles of F. graminearum mycotoxins on maize seedling blight occurring at Zhang Ye of Gansu, China, 23 isolates of F. graminearum were collected and characterized. A PCR assay showed all 23 isolates belonged to the 15-acetyldeoxynivalenol (15-ADON) genotype. This was also confirmed by production of both DON and 15-ADON in either rice culture medium or maize seedling roots, detected by high performance liquid chromatography and mass spectrometry. In maize seedling roots, 15-ADON dominated at 6 days post inoculation (dpi) and DON was the main mycotoxin at 12 dpi. The biomass of F. graminearum doubled from 6 to 12 dpi, and was positively correlated with virulence of the isolates. Both mycotoxins affected maize root vitality, but 15-ADON had a greater effect than DON. ALDH9 and MDH, two dehydrogenase synthesis genes in maize, showed a lower relative expression in 15-ADON treatments than in DON treatments. It indicated that both mycotoxins affected seed germination and root development, with 15-ADON being more destructive. Under scanning electron microscopy and transmission electron microscopy, root hair formation and development were delayed by DON, but completely inhibited by 15-ADON. 15-ADON caused cell shrinkage, loose cellular structure, and widened intercellular spaces; it also destroyed organelles and caused plasmolysis, and eventually ruptured cell membranes causing cell death. DON did not affect cell morphology and arrangement, but altered the morphology of organelles, forming concentric membranous bodies and a large amount of irregular lipid droplets. Thus, both mycotoxins contributed to symptom expression of maize seedling blight, but 15-ADON was more destructive than DON.

Arabidopsis plasma membrane H+-ATPase genes AHA2 and AHA7 have distinct and overlapping roles in the modulation of root tip H+ efflux in response to low-phosphorus stress.

Phosphorus deficiency in soil is one of the major limiting factors for plant growth. Plasma membrane H+-ATPase (PM H+-ATPase) plays an important role in the plant response to low-phosphorus stress (LP). However, few details are known regarding the action of PM H+-ATPase in mediating root proton (H+) flux and root growth under LP. In this study, we investigated the involvement and function of different Arabidopsis PM H+-ATPase genes in root H+ flux in response to LP. First, we examined the expressions of all Arabidopsis PM H+-ATPase gene family members (AHA1-AHA11) under LP. Expression of AHA2 and AHA7 in roots was enhanced under this condition. When the two genes were deficient in their respective Arabidopsis mutant plants, root growth and responses of the mutants to LP were highly inhibited compared with the wild-type plant. AHA2-deficient plants exhibited reduced primary root elongation and lower H+ efflux in the root elongation zone. AHA7-deficient plants exhibited reduced root hair density and lower H+ efflux in the root hair zone. The modulation of H+ efflux by AHA2 or AHA7 was affected by the action of 14-3-3 proteins and/or auxin regulatory pathways in the context of root growth and response to LP. Our results suggest that under LP conditions, AHA2 acts mainly to modulate primary root elongation by mediating H+ efflux in the root elongation zone, whereas AHA7 plays an important role in root hair formation by mediating H+ efflux in the root hair zone.

Inoculation with Bacillus licheniformis MH48 Promotes Nutrient Uptake in Seedlings of the Ornamental Plant Camellia japonica grown in Korean Reclaimed Coastal Lands

The objective of this study was to determine whether inoculation with Bacillus licheniformis MH48 as a plant growth-promoting rhizobacterium (PGPR) could promote nutrient uptake of seedlings of the ornamental plant Camellia japonica in the Saemangeum reclaimed coastal land in Korea. B. licheniformis MH48 inoculation increased total nitrogen and phosphorus content in soils by 2.2 and 20.0 fold, respectively, compared to those without bacterial inoculation. In addition, B. licheniformis MH48 produced auxin, which promoted the formation of lateral roots and root hairs, decreased production of growth-inhibiting ethylene, and alleviated salt stress. Total nitrogen and phosphorus uptake of seedlings subjected to bacterial inoculation was 2.3 and 3.6 fold higher, respectively, than the control. However, B. licheniformis MH48 inoculation had no significant effect on the growth of seedlings. Our results suggest that inoculation with B. licheniformis MH48 can be used as a PGPR bio - enhancer to stimulate fine root development, promote nutrient uptake and alleviate salt stress in ornamental plant seedlings grown in the high-salinity conditions of reclaimed coastal land.

The Histone Chaperone NRP1 Interacts with WEREWOLF to Activate GLABRA2 in Arabidopsis Root Hair Development.

NUCLEOSOME ASSEMBLY PROTEIN1 (NAP1) defines an evolutionarily conserved family of histone chaperones and loss of function of the Arabidopsis thaliana NAP1 family genes NAP1-RELATED PROTEIN1 (NRP1) and NRP2 causes abnormal root hair formation. Yet, the underlying molecular mechanisms remain unclear. Here, we show that NRP1 interacts with the transcription factor WEREWOLF (WER) in vitro and in vivo and enriches at the GLABRA2 (GL2) promoter in a WER-dependent manner. Crystallographic analysis indicates that NRP1 forms a dimer via its N-terminal α-helix. Mutants of NRP1 that either disrupt the α-helix dimerization or remove the C-terminal acidic tail, impair its binding to histones and WER and concomitantly lead to failure to activate GL2 transcription and to rescue the nrp1-1 nrp2-1 mutant phenotype. Our results further demonstrate that WER-dependent enrichment of NRP1 at the GL2 promoter is involved in local histone eviction and nucleosome loss in vivo. Biochemical competition assays imply that the association between NRP1 and histones may counteract the inhibitory effect of histones on the WER-DNA interaction. Collectively, our study provides important insight into the molecular mechanisms by which histone chaperones are recruited to target chromatin via interaction with a gene-specific transcription factor to moderate chromatin structure for proper root hair development.

Glucose and sucrose differentially modify cell proliferation in maize during germination

Glucose and sucrose play a dual role: as carbon and energy sources and as signaling molecules. In order to address the impact that sugars may have on maize seeds during germination, embryo axes were incubated with or without either of the two sugars. Expression of key cell cycle markers and protein abundance, cell patterning and de novo DNA synthesis in root meristem zones were analyzed. Embryo axes without added sugars in imbibition medium were unable to grow after 7 days; in sucrose, embryo axes developed seminal and primary roots with numerous root hairs, whereas in glucose axes showed a twisted morphology, no root hair formation but callus-like structures on adventitious and primary seminal roots. More and smaller cells were observed with glucose treatment in root apical meristems. de novo DNA synthesis was stimulated more by glucose than by sucrose. At 24 h of imbibition, expression of ZmCycD2;2a and ZmCycD4;2 was increased by sucrose and reduced by glucose. CDKA1;1 and CDKA2;1 expression was stimulated equally by both sugars. Protein abundance patterns were modified by sugars: ZmCycD2 showed peaks on glucose at 12 and 36 h of imbibition whereas sucrose promoted ZmCycD3 protein accumulation. In presence of glucose ZmCycD3, ZmCycD4 and ZmCycD6 protein abundance was reduced after 24 h. Finally, both sugars stimulated ZmCDKA protein accumulation but at different times. Overall, even though glucose appears to act as a stronger mitogen stimulator, sucrose stimulated the expression of more cell cycle markers during germination. This work provides evidence of a differential response of cell cycle markers to sucrose and glucose during maize germination that may affect the developmental program during plantlet establishment.

Tracheophytes Contain Conserved Orthologs of a Basic Helix-Loop-Helix Transcription Factor That Modulate ROOT HAIR SPECIFIC Genes.

ROOT HAIR SPECIFIC (RHS) genes, which contain the root hair-specific cis-element (RHE) in their regulatory regions, function in root hair morphogenesis. Here, we demonstrate that an Arabidopsis thaliana basic helix-loop-helix transcription factor, ROOT HAIR DEFECTVE SIX-LIKE4 (RSL4), directly binds to the RHE in vitro and in vivo, upregulates RHS genes, and stimulates root hair formation in Arabidopsis. Orthologs of RSL4 from a eudicot (poplar [Populus trichocarpa]), a monocot (rice [Oryza sativa]), and a lycophyte (Selaginella moellendorffii) each restored root hair growth in the Arabidopsis rsl4 mutant. In addition, the rice and S. moellendorffii RSL4 orthologs bound to the RHE in in vitro and in vivo assays. The RSL4 orthologous genes contain RHEs in their promoter regions, and RSL4 was able to bind to its own RHEs in vivo and amplify its own expression. This process likely provides a positive feedback loop for sustainable root hair growth. When RSL4 and its orthologs were expressed in cells in non-root-hair positions, they induced ectopic root hair growth, indicating that these genes are sufficient to specify root hair formation. Our results suggest that RSL4 mediates root hair formation by regulating RHS genes and that this mechanism is conserved throughout the tracheophyte (vascular plant) lineage.

Superior Root Hair Formation Confers Root Efficiency in Some, But Not All, Rice Genotypes upon P Deficiency.

Root hairs are a low-cost way to extend root surface area (RSA), water and nutrient acquisition. This study investigated to what extend variation exists for root hair formation in rice in dependence of genotype, phosphorus (P) supply, growth medium, and root type. In general, genotypic variation was found for three root hair properties: root hair length, density, and longevity. In low P nutrient solution more than twofold genotypic difference was detected for root hair length while only onefold variation was found in low P soil. These differences were mostly due to the ability of some genotypes to increase root hair length in response to P deficiency. In addition, we were able to show that a higher proportion of root hairs remain viable even in mature, field-grown plants under low P conditions. All investigated root hair parameters exhibited high correlations across root types which were always higher in the low P conditions compared to the high P controls. Therefore we hypothesize that a low P response leads to a systemic signal in the entire root system. The genotype DJ123 consistently had the longest root hairs under low P conditions and we estimated that, across the field-grown root system, root hairs increased the total RSA by 31% in this genotype. This would explain why DJ123 is considered to be very root efficient in P uptake and suggests that DJ123 should be utilized as a donor in breeding for enhanced P uptake. Surprisingly, another root and P efficient genotype seemed not to rely on root hair growth upon P deficiency and therefore must contain different methods of low P adaptation. Genotypic ranking of root hair properties did change substantially with growth condition highlighting the need to phenotype plants in soil-based conditions or at least to validate results obtained in solution-based growth conditions.

Morphological and structural characterization of the attachment system in aerial roots of Syngonium podophyllum.

The attachment of aerial roots of Syngonium podophyllum involves a multi-step process adjusted by multi-scale structures. Helical-crack root hairs are first found in the attachment system, representing specialized structures for surface anchorage. The morphological variability of attachment organs reflects diverse climbing strategies. One such anchoring mode in clinging-climbers involves the time-dependent interaction between roots and the support: By naturally occurring adhesive roots with root hairs, the plant can ascend on supports of any shape and size. As a typical root-climber, Syngonium podophyllum develops elongate aerial roots at nodes. Here, we studied its attachment behavior from the external morphology to the internal structure in detail. Through SEM and LM observation on several root-substrate interfaces, we suggested that the attachment of aerial roots was mediated by a multi-step process, in which root hairs played significant roles in releasing mucilaginous substance and securing the durable anchorage. We summarized all the types of shape changes of root hairs with particular focus on the abnormal transition from a tube to a helical-crack ribbon. We demonstrated our understanding with respect to the formation of the helical-crack root hairs, based on the structural evidence of cellulose microfibrils orientation on the cell wall lamellae. The helical-crack root hairs serving as energy-dissipating units retard the failure of adhesion under high winds and loads.

S-nitrosoglutathione promotes cell wall remodelling, alters the transcriptional profile and induces root hair formation in the hairless root hair defective 6 (rhd6) mutant of Arabidopsis thaliana.

Nitric oxide (NO) exerts pleiotropic effects on plant development; however, its involvement in cell wall modification during root hair formation (RHF) has not yet been addressed. Here, mutants of Arabidopsis thaliana with altered root hair phenotypes were used to assess the involvement of S-nitrosoglutathione (GSNO), the primary NO source, in cell wall dynamics and gene expression in roots induced to form hairs. GSNO and auxin restored the root hair phenotype of the hairless root hair defective 6 (rhd6) mutant. A positive correlation was observed between increased NO production and RHF induced by auxin in rhd6 and transparent testa glabra (ttg) mutants. Deposition of an epitope within rhamnogalacturonan-I recognized by the CCRC-M2 antibody was delayed in root hair cells (trichoblasts) compared with nonhair cells (atrichoblasts). GSNO, but not auxin, restored the wild-type root glycome and transcriptome profiles in rhd6, modulating the expression of a large number of genes related to cell wall composition and metabolism, as well as those encoding ribosomal proteins, DNA and histone-modifying enzymes and proteins involved in post-translational modification. Our results demonstrate that NO plays a key role in cell wall remodelling in trichoblasts and suggest that it also participates in chromatin modification in root cells of A.thaliana.

Nitric oxide signaling is involved in the response to iron deficiency in the woody plant Malus xiaojinensis

To cope with iron (Fe) deficiency, plants have evolved a wide range of adaptive responses from changes in morphology to altered physiological responses. Recent studies have demonstrated that nitric oxide (NO) is involved in the Fe-deficiency response through hormonal signaling pathways. Here, we report that NO plays a significant role in Malus xiaojinensis, an Fe-efficient woody plant. Fe deficiency triggered significant accumulation of NO in the root system, predominantly in the outer cortical and epidermal cells of the elongation zone. The NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO) completely arrested Fe deficiency-induced root hair formation, blocked the increase in root ferric-chelate reductase activity and in root H+ excretion, further reduced the active iron content in young leaves and roots, and prevented the upregulation of the critical Fe-related genes, FIT, MxFRO2-like, and MxIRT1. These conditions were restored under Fe deficiency by treatment with the NO donor, sodium nitroprusside (SNP). Additionally, chlorophyll content and relative expression levels of the genes chlorophyll a deoxygenase (MxCAO) and polyamine oxidase (MxPAO) were not changed significantly following Fe deficiency for 6 d; however, SNP treatment increased MxHEMA gene expression. Interestingly, the Fv/Fm ratio, the maximum quantum yield of photosystem II (PSII), decreased significantly following cPTIO treatment. We observed more severe chlorosis under Fe deficiency with cPTIO treatment for 9 d. These results strongly suggest that NO mediates a range of responses to Fe deficiency in M. xiaojinensis, from morphological changes to the regulation of physiological processes and gene expression.

Soil ammonia volatilization following urea application suppresses root hair formation and reduces seed germination in six wheat varieties

Poor seed germination and early seedling growth caused by ammonia toxicity following urea application are major constraints for wheat production. This study aims to determine ammonia volatilization caused by urea and its damage to seed germination, early seedling growth, and its associated physiological mechanism. Two petri dish experiments were conducted under four nitrogen (N) application rates (0, 0.58, 1.16 and 1.75mgNg−1 soil) for six wheat varieties that differ in their ammonia tolerance with regard to the germination percentage (%), its associated indicator, related growth parameters, root hair development and changes in the content of endogenous hormones. Increasing the N rate significantly increased ammonia volatilization from 9.69 to 121.9mg per pot and therefore reduced the germination percentage (%) by 51%–95% and suppressed root and shoot growth (P≤0.05). The variation in the response of the different genotypes to ammonia toxicity was distinguishing. Root was more sensitive to ammonia volatilization than shoot. Ammonia toxicity seriously suppressed root hair formation, and the varieties that were tolerant of ammonia toxicity could sustain relatively more abundant root hair formation compared with the other more sensitive varieties. The specific balance between several endogenous plant hormones was also found in response to ammonia toxicity between two varieties with contrasting tolerance. This study emphasized the potential to select varieties with high tolerance to ammonia toxicity to improve seed germination and early seedling establishment through a breeding programme. The physiological mechanisms of seed germination responsible for high tolerance to ammonia toxicity are rapid root hair formation and the synergistic effect between several endogenous plant hormones.

Analysis of plant growth-promoting properties of Bacillusamyloliquefaciens UCMB5113 using Arabidopsis thaliana as host plant

Main conclusionThis study showed thatBacillusamyloliquefaciensUCMB5113 colonizingArabidopsisroots changed root structure and promoted growth implying the usability of this strain as a novel tool to support sustainable crop production.Root architecture plays a crucial role for plants to ensure uptake of water, minerals and nutrients and to provide anchorage in the soil. The root is a dynamic structure with plastic growth and branching depending on the continuous integration of internal and environmental factors. The rhizosphere contains a complex microbiota, where some microbes can colonize plant roots and support growth and stress tolerance. Here, we report that the rhizobacterium Bacillus amyloliquefaciens subsp. plantarum UCMB5113 stimulated the growth of Arabidopsisthaliana Col-0 by increased lateral root outgrowth and elongation and root-hair formation, although primary root elongation was inhibited. In addition, the growth of the above ground tissues was stimulated by UCMB5113. Specific hormone reporter gene lines were tested which suggested a role for at least auxin and cytokinin signaling during rhizobacterial modulation of Arabidopsis root architecture. UCMB5113 produced cytokinins and indole-3-acetic acid, and the formation of the latter was stimulated by root exudates and tryptophan. The plant growth promotion effect by UCMB5113 did not appear to depend on jasmonic acid in contrast to the disease suppression effect in plants. UCMB5113 exudates inhibited primary root growth, while a semi-purified lipopeptide fraction did not and resulted in the overall growth promotion indicating an interplay of many different bacterial compounds that affect the root growth of the host plant. This study illustrates that beneficial microbes interact with plants in root development via classic and novel signals.

Cu from dissolution of CuO nanoparticles signals changes in root morphology

Utilization of CuO nanoparticles (NPs) in agriculture, as fertilizers or pesticides, requires understanding of their impact on plant metabolism. Inhibition of root elongation by CuO NPs (>10 mg Cu/kg) occurred in wheat grown in sand. Morphological changes included root hair proliferation and shortening of the zones of division and elongation. The epidermal cells in the compressed root tip were abnormal in shape and file patterning but staining with SYTOX Blue did not reveal a general increase in epidermal cell death. Inhibition of root elongation and proliferation of root hair formation occurred also in response to exogenous indole acetic acid (IAA) supplied through tryptophan metabolism by the root-colonizing bacterium, Pseudomonas chlororaphis O6. Altered root morphology caused by the CuO NPs was likely due to release of Cu from dissolution at the root surface because similar changes occurred with Cu ions (≥6 mg/kg). Use of a fluorescent probe showed the accumulation of nitric oxide (NO), required for root hair formation, was not changed by the NPs. These findings suggested that dissolution of the NPs in the rhizosphere resulted levels of Cu that modified IAA distribution to causing root shortening but permitted NO cell signaling to promote root hair proliferation.

Exogenous application of abscisic acid (ABA) increases root and cell hydraulic conductivity and abundance of some aquaporin isoforms in the ABA-deficient barley mutant Az34.

Background and Aims Regulation of water channel aquaporins (AQPs) provides another mechanism by which abscisic acid (ABA) may influence water flow through plants. To the best of our knowledge, no studies have addressed the changes in ABA levels, the abundance of AQPs and root cell hydraulic conductivity (LpCell) in the same tissues. Thus, we followed the mechanisms by which ABA affects root hydraulics in an ABA-deficient barley mutant Az34 and its parental line 'Steptoe'. We compared the abundance of AQPs and ABA in cells to determine spatial correlations between AQP abundance and local ABA concentrations in different root tissues. In addition, abundance of AQPs and ABA in cortex cells was related to LpCell. Methods Root hydraulic conductivity (LpRoot) was measured by means of root exudation analyses and LpCell using a cell pressure probe. The abundance of ABA and AQPs in root tissues was assessed through immunohistochemical analyses. Isoform-specific antibodies raised against HvPIP2;1, HvPIP2;2 and HvPIP2;5 were used. Key Results Immunolocalization revealed lower ABA levels in root tissues of Az34 compared with 'Steptoe'. Root hydraulic conductivity (LpRoot) was lower in Az34, yet the abundance of HvPIPs in root tissues was similar in the two genotypes. Root hair formation occurred closer to the tip, while the length of the root hair zone was shorter in Az34 than in 'Steptoe'. Application of external ABA to the root medium of Az34 and 'Steptoe' increased the immunostaining of root cells for ABA and for HvPIP2;1 and HvPIP2;2 especially in root epidermal cells and the cortical cell layer located beneath, parallel to an increase in LpRoot and LpCell. Treatment of roots with Fenton reagent, which inhibits AQP activity, prevented the ABA-induced increase in root hydraulic conductivity. Conclusion Shortly after (<2 h) ABA application to the roots of ABA-deficient barley, increased tissue ABA concentrations and AQP abundance (especially the plasma-membrane localized isoforms HvPIP2;1 and HvPIP2;2) were spatially correlated in root epidermal cells and the cortical cell layer located beneath, in conjunction with increased LpCell of the cortical cells. In contrast, long-term ABA deficiency throughout seedling development affects root hydraulics through other mechanisms, in particular the developmental timing of the formation of root hairs closer to the root tip and the length of the root hair zone.

The LIKE SEX FOUR2 regulates root development by modulating reactive oxygen species homeostasis in Arabidopsis.

Maintaining reactive oxygen species (ROS) homeostasis plays a central role in plants, and is also critical for plant root development. Threshold levels of ROS act as signals for elongation and differentiation of root cells. The protein phosphatase LIKE SEX FOUR2 (LSF2) has been reported to regulate starch metabolism in Arabidopsis, but little is known about the mechanism how LSF2 affect ROS homeostasis. Here, we identified that LSF2 function as a component modulating ROS homeostasis in response to oxidative stress and, thus regulate root development. Compared with wild type Arabidopsis, lsf2-1 mutant exhibited reduced rates of superoxide generation and higher levels of hydrogen peroxide upon oxidative stress treatments. The activities of several antioxidant enzymes, including superoxide dismutase, catalase, and ascorbate peroxidase, were also affected in lsf2-1 mutant under these oxidative stress conditions. Consequently, lsf2-1 mutant exhibited the reduced root growth but less inhibition of root hair formation compared to wild type Arabidopsis plants. Importantly, protein phosphatase LSF2 interacted with mitogen-activated protein kinase 8 (MPK8), a known component of ROS homeostasis pathways in the cytoplasm. These findings indicated the novel function of LSF2 that controls ROS homeostasis to regulate root development.

Rhizosphere priming of barley with and without root hairs

The influence of plant roots and the associated rhizosphere activities on decomposition of soil organic matter (SOM), the rhizosphere priming effect, has emerged as a crucial mechanism regulating global carbon (C) and nitrogen (N) cycles. However, the role of root morphology in controlling the rhizosphere priming effect remains largely unknown. To investigate the link between root hairs, a critical part of the entire root morphology, and the rhizosphere priming effect, we grew a barley wild type and a barley mutant without root hairs in a greenhouse and continuously labeled them with 13C-depleted CO2. Soil CO2 efflux was measured during tillering and head-emergence stages of plant growth. Based on its δ13C signature, total CO2 was partitioned for root-derived and SOM-derived CO2, and the SOM decomposition primed in the rhizosphere was calculated. Soil microbial biomass C and N, and the activities of six extracellular enzymes (β-cellobiohydrolase, β-glucosidase, acid phosphatase, β-xylosidase, leucin-aminopeptidase, and N-acetyl-β-glucosaminidase) were measured to test the effects of root hairs.During the early stage of development (tillering), when plants were sufficiently supplied with nutrients, the barley mutant without root hairs produced more shoot biomass. In contrast, high C costs for root-hair formation likely reduced the growth of the barley wild type. At this stage, the wild type with regular root hairs produced a positive rhizosphere priming effect (69% increase), but the mutant without root hairs produced a negative priming effect on SOM decomposition (28% decline). At the head-emergence stage, when nutrients were scarce, plant biomass production of the mutant was reduced, probably due to inefficient nutrient uptake in the absence of root hairs. At this stage, both barley types produced positive rhizosphere priming effects (72% and 209% increase for the wild type and the mutant, respectively) and the microbial biomass was higher for both planted soils compared to the tillering stage. Extracellular enzymes responsible for the decomposition of stable SOM had higher activities in cases of positive priming effects. Overall, root hairs played an important role in regulating rhizosphere priming.

The ectopic localization of CAPRICE LIKE MYB3 protein in Arabidopsis root epidermis

Cell fate determination is a critical step of plant morphogenesis. Root hair and trichome formation is a good model for studying cell fate determination. The gene CAPRICE (CPC) encodes an R3 type MYB transcription factor, promotes root hair formation, and inhibits trichome formation in Arabidopsis thaliana. The CPC homologous gene CPC LIKE MYB3 (CPL3) encoded 66% similar amino acid sequence to CPC, and it also possessed a cell-to-cell movement WxM motif. CPC protein moves from non-hair cells to neighboring root hair forming cells and induces root hair formation in Arabidopsis root epidermal cells. In this study, to investigate the function and cell-to-cell movement ability of CPL3, we generated CPC:CPL3:GFP transgenic plants to compare against CPL3:CPL3:GFP transgenic plants. CPC:CPL3:GFP transgenic plants showed no-trichome and many root-hair phenotypes, confirming similar function of CPL3 to CPC in root hair and trichome cell fate determination. However, CPL3:GFP fusion protein localized exclusively in non-hair cells in CPC:CPL3:GFP transgenic plants. Collectively, our results suggest that the CPL3 protein does not have cell-to-cell movement ability. Our findings indicate that the CPC family includes a movement protein and a protein that does not move. We believe our results provide new insight into the regulatory mechanism that mediates epidermal cell fate determination.