Changes In Cell Wall Composition Research Articles

Boron deficiency disorders the cell wall in Neolamarckia cadamba

Boron (B) is an essential element for plant growth and development as it regulates numerous biological processes. Despite years of research on the role of B in regulating plant growth, changes in cell wall composition due to B deficiencyremain unclear. Here, we study B deficiency on the physiology and transcriptome of Neolamarckia cadamba, a fast-growing woody plant with diverse applications. B deficiency induces severe morphological and anatomical changes in N. cadamba including reduced seedling growth, significant inhibition of shoot tip growth and leaves. B deficiency also resulted in oxidative damage and decreasing B concentration in plant. In addition, enhancing activation of the phenylalanine ammonia lyase (PAL) and phenylpropanoid biosynthesis pathways resulted in increased shoot tip lignification. Pectin content decreased and the genes related to the synthesis of pectin and cellulose in mature leaves of N. cadamba changed expression levels in response to B deficiency. Moreover, BOR1, a potential B transporter, was differentially over-expressed under B deficiency in different tissues. Taking together, we can conclude that adaptive changes in N. cadamba cell walls to respond to B deficiency can potentially be utilized for genetic engineering and breeding for low B tolerance.

Plant priming changes physiological properties and lignin content in Miscanthus x giganteus

During the last couple of years, the traditionally mild climate of central Europe changed to very hot and dry (including the spring season). Local plants and crops need to deal with this stressful change causing a yield decrease. Primary aims were to explore simple ways of "hardening" Miscanthus x giganteus J.M.Greef, Deuter ex Hodk., Renvoize energy grass to deal with climate changes more efficiently and improve its productivity as a biomass crop at the same time. Plant priming has been discussed as a cheap and simple tool for the improvement of plant qualities. Specific doses of vitamins, metals as priming compounds, and different initial cultivation conditions (cold, hot, dark) were applied to study changes in plant physiology using non-invasive methods of measurement of leaf fluorescence and reflectance. After a short priming period, all plants studied were cultivated in a greenhouse under conditions mimicking the latest climate trend. Copper application and cold treatment (10 °C) increased the synthesis of lignin in treated plants. Nitrogen supplementation had the opposite effect; lignin production decreased. All treatments had a significant influence on photosynthetic processes; bud did not negatively influence the production of photosynthetic pigments. Obtained results show that applying particular physical and chemical primers to young Miscanthus x giganteus can result in substantial physiological changes, mainly concerning the effectivity of photosynthesis and change in cell wall composition.

Dynamic changes in cell wall composition of mature sunflower leaves under distinct water regimes affect photosynthesis.

In previous work, we identified that exposure to limited water availability induced changes in cell wall composition of mature Helianthus annuus L. leaves that affected mesophyll conductance to CO2 diffusion (gm). However, it is unclear on which timescale these changes in cell wall composition occurred. Here, we subjected H. annuus to control (i.e. water availability), different levels of short-term water deficit stress (ST), long-term water deficit stress (LT), and long-term water deficit stress followed by gradual recoveries addressed at different timescales (LT-Rec) to evaluate the dynamics of modifications in the main composition of cell wall (cellulose, hemicelluloses, pectins and lignins) affecting photosynthesis. During gradual ST treatments, pectins enhancement was associated with gm decline. However, during LT-Rec, pectins content decreased significantly after only 5 h, while hemicelluloses and lignins amounts changed after 24 h, all being uncoupled from gm. Surprisingly, lignins increased by around 200% compared with control and were related to stomatal conductance to gas diffusion (gs) during LT-Rec. Although we suspect that the accuracy of the protocols to determine cell wall composition should be re-evaluated, we demonstrate for the first time that a highly dynamic cell wall composition turnover differently affects photosynthesis in plants subjected to distinct water regimes.

Adjustments in photosynthesis and leaf water relations are related to changes in cell wall composition in Hordeum vulgare and Triticum aestivum subjected to water deficit stress

In the current climate change scenario, understanding crops’ physiological performance under water shortage is crucial to overcome drought periods. Although the implication of leaf water relations maintaining leaf turgor and stomatal functioning under water deprivation has been suggested, the relationships between photosynthesis and osmotic and elastic adjustments remain misunderstood. Similarly, only few studies in dicotyledonous analysed how changes in cell wall composition affected photosynthesis and leaf water relations under drought. To induce modifications in photosynthesis, leaf water relations and cell wall composition, Hordeum vulgare and Triticum aestivum were subjected to different water regimes: control (CL, full irrigation), moderate and severe water deficit stress (Mod WS and Sev WS, respectively). Water shortage decreased photosynthesis mainly due to stomatal conductance (gs) declines, being accompanied by reduced osmotic potential at full turgor (πo) and increased bulk modulus of elasticity (ε). Whereas both species enhanced pectins when intensifying water deprivation, species-dependent adjustments occurred for cellulose and hemicelluloses. From these results, we showed that πo and ε influenced photosynthesis, particularly, gs. Furthermore, the (Cellulose+Hemicelluloses)/Pectins ratio determined ε and mesophyll conductance (gm) in grasses, presenting the lowest pectins content within angiosperms. Thus, we highlight the relevance of cell wall composition regulating grasses physiology during drought acclimation.

Ketoconazole resistant Candida albicans is sensitive to a wireless electroceutical wound care dressing

Wireless electroceutical dressing (WED) fabric kills bacteria and disrupts bacterial biofilm. This work tested, comparing with standard of care topical antibiotic ketoconazole, whether the weak electric field generated by WED is effective to manage infection caused by ketoconazole-resistant yeast Candida albicans. WED inhibited Candida albicans biofilm formation and planktonic growth. Unlike ketoconazole, WED inhibited yeast to hyphal transition and downregulated EAP1 curbing cell attachment. In response to WED-dependent down-regulation of biofilm-forming BRG1 and ROB1, BCR1 expression was markedly induced in what seems to be a futile compensatory response. WED induced NRG1 and TUP1, negative regulators of filamentation; it down-regulated EFG1, a positive regulator of hyphal pathway. Consistent with the anti-hyphal properties of WED, the expression of ALS3 and HWP1 were diminished. Ketoconazole failed to reproduce the effects of WED on NRG1, TUP1 and EFG1. WED blunted efflux pump activity; this effect was in direct contrast to that of ketoconazole. WED exposure compromised cellular metabolism. In the presence of ketoconazole, the effect was synergistic. Unlike ketoconazole, WED caused membrane depolarization, changes in cell wall composition and loss of membrane integrity. This work presents first evidence that weak electric field is useful in managing pathogens which are otherwise known to be antibiotic resistant.

Silicon-mediated growth promotion in maize (Zea mays L.) occurs via a mechanism that does not involve activation of the plasma membrane H+-ATPase

Silicon (Si)-mediated growth promotion of various grasses is well documented. In the present study, Si-induced changes in maize shoot growth and its underlying mechanisms were studied. Maize plants were grown with various concentrations of Si (0–3 mM) in the nutrient solution. Silicon nutrition improved plant expansion growth. Silicon-supplied maize plants (0.8 and 1.2 mM) showed higher plant height and leaf area compared to no-Si amended plants. It was assumed that Si-induced expansion growth was due to positive Si effects on plasma membrane (PM) H+-ATPase. In this context, western blot analysis revealed an increase in PM H+-ATPase abundance by 77% under Si nutrition. However, in vitro measurements of enzyme activities showed no significant effect on apoplast pH, proton pumping, passive H+ efflux and enzyme kinetics such as Km, Vmax, and activation energy. Further, these results were confirmed by in vivo ratiometric analysis of apoplastic pH, which showed non-significant changes upon Si supply. In contrast, 1 mM Si altered the relative transcripts of specific PM H+-ATPase isoforms. Silicon application resulted in a significant decrease of MHA3, and this decrease in transcription seems to be compensated by an increased concentration of H+-ATPase protein. From these results, it can be concluded that changes in cell wall composition and PM H+-ATPase may be responsible for Si-mediated growth improvement in maize.

Proso millet (Panicum miliaceum L.): A potential crop to meet demand scenario for sustainable saline agriculture

Proso millet (Panicum miliaceum L.) is resilient to abiotic stress, especially to land degradation caused by soil salinization. However, the mechanisms by which its roots adapt and tolerate salt stress are obscure. In this study, plants of a salt-sensitive cultivar (SS 212) and a salt-tolerant cultivar (ST 47) of proso millet were exposed to severe salt stress and subsequent re-watering. ST 47 exhibited greater salt tolerance than SS 212, as evidenced by higher increases in total root length (TRL), root surface area (RSA), root tip number (RTN). Moreover, microstructural analysis showed that relative to SS 212, the roots of ST 47 could maintain more intact internal structures and thicker cell walls under salt stress. Digital RNA sequence analysis revealed that ST 47 maintained better Na+/K+ balance to resist Na+ toxicity via a higher capability to restrict Na+ uptake, vacuolar Na+ sequestration, and Na+ exclusion. The mechanism for Na+ toxicity resistance in ST 47 involved promoting cell wall composition changes via efficient regulation of galactose metabolism and biosynthesis of cellulose and phenylpropanoids. Overall, this study provides valuable salt-tolerant cultivar resources and mechanisms for regulating salt tolerance, which could be applied for the rehabilitation of saline lands.

Tracking cell wall changes in wine and table grapes undergoing Botrytis cinerea infection using glycan microarrays.

The necrotrophic fungus Botrytis cinerea infects a broad range of fruit crops including domesticated grapevine Vitis vinifera cultivars. Damage caused by this pathogen is severely detrimental to the table and wine grape industries and results in substantial crop losses worldwide. The apoplast and cell wall interface is an important setting where many plant-pathogen interactions take place and where some defence-related messenger molecules are generated. Limited studies have investigated changes in grape cell wall composition upon infection with B. cinerea, with much being inferred from studies on other fruit crops. In this study, comprehensive microarray polymer profiling in combination with monosaccharide compositional analysis was applied for the first time to investigate cell wall compositional changes in the berries of wine (Sauvignon Blanc and Cabernet Sauvignon) and table (Dauphine and Barlinka) grape cultivars during Botrytis infection and tissue maceration. This was used in conjunction with scanning electron microscopy (SEM) and X-ray computed tomography (CT) to characterize infection progression. Grapes infected at veraison did not develop visible infection symptoms, whereas grapes inoculated at the post-veraison and ripe stages showed evidence of significant tissue degradation. The latter was characterized by a reduction in signals for pectin epitopes in the berry cell walls, implying the degradation of pectin polymers. The table grape cultivars showed more severe infection symptoms, and corresponding pectin depolymerization, compared with wine grape cultivars. In both grape types, hemicellulose layers were largely unaffected, as was the arabinogalactan protein content, whereas in moderate to severely infected table grape cultivars, evidence of extensin epitope deposition was present. Specific changes in the grape cell wall compositional profiles appear to correlate with fungal disease susceptibility. Cell wall factors important in influencing resistance may include pectin methylesterification profiles, as well as extensin reorganization.

Paraffin oil induces resistance against powdery mildew in grapevine through salicylic acid signaling.

Mineral oils have been widely used in the pest control of several crops. However, their mode of action is poorly understood, especially in the case of their antifungal properties. The possible direct fungicidal activity and the stress-inducing capability of paraffin oil on grapevine were examined using Vitis vinifera L. cv 'Kékfrankos' cuttings and the fungus Erysiphe necator, the causal agent of powdery mildew. Our experiments demonstrated that paraffin oil does not have fungicide activity on E. necator, but induces significant stress-related changes in grapevine physiology. Elevated H2 O2 production and the accumulation of the phytohormone salicylic acid were measured. Secondary thickening of the cell wall by lignin deposition and the accumulation of phenolic compounds were also observed. Some enzyme activities related to the detoxification of reactive oxygen species, disease response, and the synthesis of lignin were changed in accordance with the determined changes in cell wall composition and H2 O2 levels. The results suggest that paraffin oil induces stress responses on grapevine leaves through oxidative burst, and this response is systemized by salicylic acid. The accumulation of lignin and water-soluble phenolics may be directly responsible for the paraffin oil-induced resistance of grapevine against powdery mildew. © 2021 Society of Chemical Industry.

BdERECTA controls vasculature patterning and phloem-xylem organization in Brachypodium distachyon

BackgroundThe vascular system of plants consists of two main tissue types, xylem and phloem. These tissues are organized into vascular bundles that are arranged into a complex network running through the plant that is essential for the viability of land plants. Despite their obvious importance, the genes involved in the organization of vascular tissues remain poorly understood in grasses.ResultsWe studied in detail the vascular network in stems from the model grass Brachypodium distachyon (Brachypodium) and identified a large set of genes differentially expressed in vascular bundles versus parenchyma tissues. To decipher the underlying molecular mechanisms of vascularization in grasses, we conducted a forward genetic screen for abnormal vasculature. We identified a mutation that severely affected the organization of vascular tissues. This mutant displayed defects in anastomosis of the vascular network and uncommon amphivasal vascular bundles. The causal mutation is a premature stop codon in ERECTA, a LRR receptor-like serine/threonine-protein kinase. Mutations in this gene are pleiotropic indicating that it serves multiple roles during plant development. This mutant also displayed changes in cell wall composition, gene expression and hormone homeostasis.ConclusionIn summary, ERECTA has a pleiotropic role in Brachypodium. We propose a major role of ERECTA in vasculature anastomosis and vascular tissue organization in Brachypodium.

Defects in Cell Wall Differentiation of the Arabidopsis Mutant rol1-2 Is Dependent on Cyclin-Dependent Kinase CDK8.

Plant cells are encapsulated by cell walls whose properties largely determine cell growth. We have previously identified the rol1-2 mutant, which shows defects in seedling root and shoot development. rol1-2 is affected in the Rhamnose synthase 1 (RHM1) and shows alterations in the structures of Rhamnogalacturonan I (RG I) and RG II, two rhamnose-containing pectins. The data presented here shows that root tissue of the rol1-2 mutant fails to properly differentiate the cell wall in cell corners and accumulates excessive amounts of callose, both of which likely alter the physical properties of cells. A surr (suppressor of the rol1-2 root developmental defect) mutant was identified that alleviates the cell growth defects in rol1-2. The cell wall differentiation defect is re-established in the rol1-2 surr mutant and callose accumulation is reduced compared to rol1-2. The surr mutation is an allele of the cyclin-dependent kinase 8 (CDK8), which encodes a component of the mediator complex that influences processes central to plant growth and development. Together, the identification of the surr mutant suggests that changes in cell wall composition and turnover in the rol1-2 mutant have a significant impact on cell growth and reveals a function of CDK8 in cell wall architecture and composition.

The chitin deacetylase PoCda7 is involved in the pathogenicity of Pyricularia oryzae

The fungal cell wall plays an essential role in maintaining cellular integrity and facing complex and changing environmental conditions. Whether a fungus successfully invades a host depends on whether it evades the plant's innate immune system, which recognizes the conserved components of the fungal cell wall, such as chitin. Fungi developed infection-related changes in cell wall composition in co-evolution with nature to solve this problem. One of the changes is the deacetylation of chitin by chitin deacetylase (CDA) to produce a polysaccharide that influences the infection of pathogenic fungi. The present study revealed the functions of PoCda7, a chitin deacetylase in Pyricularia oryzae. Phenotype analysis revealed that the knockout mutant of ΔPocda7 had no significant effect on fungal morphogenic development, including conidiation, germination, appressorial formation and cell wall of conidium and hyphae but was sensitive to reactive oxygen species. Glycerols are necessary to generate sufficient turgor in appressoria for invading the host surface. As a result of the decreased appressorium turgor pressure and decreased appressorium-mediated invasion, the fungal virulence of ΔPocda7 was significantly reduced in host plants. PoCda7 inhibited the cell death of leaves in Nicotiana benthamiana. Additionally, the expression of PoCDA7 was repressed in the early stage of infection. Subcellular localization experiments showed that PoCda7 was localized in the cell wall, and its fluorescence transferred to the EIHM and BIC when the rice blast fungus infected the rice leaf sheath, which was referred to as a candidate apoplastic effector in P. oryzae.

Adaptation of Arabidopsis halleri to extreme metal pollution through limited metal accumulation involves changes in cell wall composition and metal homeostasis.

Metallophytes constitute powerful models for the study of metal homeostasis, adaptation to extreme environments and the evolution of naturally selected traits. Arabidopsis halleri is a pseudometallophyte which shows constitutive zinc/cadmium (Zn/Cd) tolerance and Zn hyperaccumulation but high intraspecific variability in Cd accumulation. To examine the molecular basis of the variation in metal tolerance and accumulation, ionome, transcriptome and cell wall glycan array profiles were compared in two genetically close A.halleri populations from metalliferous and nonmetalliferous sites in Northern Italy. The metallicolous population displayed increased tolerance to and reduced hyperaccumulation of Zn, and limited accumulation of Cd, as well as altered metal homeostasis, compared to the nonmetallicolous population. This correlated well with the differential expression of transporter genes involved in trace metal entry and in Cd/Zn vacuolar sequestration in roots. Many cell wall-related genes were also more highly expressed in roots of the metallicolous population. Glycan array and histological staining analyses demonstrated that there were major differences between the two populations in terms of the accumulation of specific root pectin and hemicellulose epitopes. Our results support the idea that both specific cell wall components and regulation of transporter genes play a role in limiting accumulation of metals in A. halleri at contaminated sites.

Ginkgo biloba and Helianthus annuus show different strategies to adjust photosynthesis, leaf water relations, and cell wall composition under water deficit stress

Cell wall thickness (Tcw) determines photosynthesis and leaf elasticity. However, only a few studies in angiosperms addressed cell wall composition implication in regulating photosynthesis and leaf water relations through mesophyll conductance (gm) and bulk modulus of elasticity (e) adjustments, respectively. Thus, we compared the phylogenetically distant Ginkgo biloba L. and Helianthus annuus L. under control and water deprivation to study the relationship between changes in cell wall composition (cellulose, hemicelluloses, and pectins) with gm and e. Although no changes were found for Tcw, both species differently modified cell wall composition, resulting in different physiological consequences. H. annuus increased cellulose, hemicelluloses, and pectins in a similar proportion, maintaining e. Additionally, it reduced photosynthesis due to stomatal closure. G. biloba did not decrease photosynthesis and largely increased hemicelluloses, leaf mass area, and leaf density, enhancing e. Nonetheless, no association between cell wall composition and gm was found in either of the two species.

Integrative transcriptomics reveals genotypic impact on sugar beet storability

Key messageAn integrative comparative transcriptomic approach on six sugar beet varieties showing different amount of sucrose loss during storage revealed genotype-specific main driver genes and pathways characterizing storability.Sugar beet is next to sugar cane one of the most important sugar crops accounting for about 15% of the sucrose produced worldwide. Since its processing is increasingly centralized, storage of beet roots over an extended time has become necessary. Sucrose loss during storage is a major concern for the sugar industry because the accumulation of invert sugar and byproducts severely affect sucrose manufacturing. This loss is mainly due to ongoing respiration, but changes in cell wall composition and pathogen infestation also contribute. While some varieties can cope better during storage, the underlying molecular mechanisms are currently undiscovered. We applied integrative transcriptomics on six varieties exhibiting different levels of sucrose loss during storage. Already prior to storage, well storable varieties were characterized by a higher number of parenchyma cells, a smaller cell area, and a thinner periderm. Supporting these findings, transcriptomics identified changes in genes involved in cell wall modifications. After 13 weeks of storage, over 900 differentially expressed genes were detected between well and badly storable varieties, mainly in the category of defense response but also in carbohydrate metabolism and the phenylpropanoid pathway. These findings were confirmed by gene co-expression network analysis where hub genes were identified as main drivers of invert sugar accumulation and sucrose loss. Our data provide insight into transcriptional changes in sugar beet roots during storage resulting in the characterization of key pathways and hub genes that might be further used as markers to improve pathogen resistance and storage properties.

Cell wall remodeling under salt stress: Insights into changes in polysaccharides, feruloylation, lignification, and phenolic metabolism in maize.

Although cell wall polymers play important roles in the tolerance of plants to abiotic stress, the effects of salinity on cell wall composition and metabolism in grasses remain largely unexplored. Here, we conducted an in-depth study of changes in cell wall composition and phenolic metabolism induced upon salinity in maize seedlings and plants. Cell wall characterization revealed that salt stress modulated the deposition of cellulose, matrix polysaccharides and lignin in seedling roots, plant roots and stems. The extraction and analysis of arabinoxylans by size-exclusion chromatography, 2D-NMR spectroscopy and carbohydrate gel electrophoresis showed a reduction of arabinoxylan content in salt-stressed roots. Saponification and mild acid hydrolysis revealed that salinity also reduced the feruloylation of arabinoxylans in roots of seedlings and plants. Determination of lignin content and composition by nitrobenzene oxidation and 2D-NMR confirmed the increased incorporation of syringyl units in lignin of maize roots. Salt stress also induced the expression of genes and the activity of enzymes enrolled in phenylpropanoid biosynthesis. The UHPLC-MS-based metabolite profiling confirmed the modulation of phenolic profiling by salinity and the accumulation of ferulate and its derivatives 3- and 4-O-feruloyl quinate. In conclusion, we present a model for explaining cell wall remodeling in response to salinity.

Fresh, freeze-dried or cell wall samples: Which is the most appropriate to determine chemical, structural and rheological variations during apple processing using ATR-FTIR spectroscopy?

Attenuated total reflectance Fourier transform spectroscopy (ATR-FTIR) was applied on fresh (NF), freeze-dried (FD) and cell wall materials (AIS) of raw and processed apples. These samples prepared from 36 apple sets and the corresponding 72 purees, issued from different varieties, agricultural practices, storage periods and processing conditions, were used to build models including exploratory analysis, supervised classification and multivariate calibration. Fresh and freeze-dried samples presented similar fingerprint spectral variations due to processing. ATR-FTIR directly on fresh purees satisfactorily predicted textural properties such as particle average size and volume (RPD>3.0), while freeze-drying improved assessment of chemical (RPD>3.2) and rheological (RPD>3.1) parameters using partial least-squares regression. The assessment of texture and macrocomponents of purees can be obtained with a limited sample preparation. For research applications because of a need of sample preparation, changes of cell wall composition during fruit processing could be assessed in relationship with pectin degradation.

Arabinogalactan-proteins of Zostera marina L. contain unique glycan structures and provide insight into adaption processes to saline environments

Seagrasses evolved from monocotyledonous land plants that returned to the marine habitat. This transition was accomplished by substantial changes in cell wall composition, revealing habitat-driven adaption to the new environment. Whether arabinogalactan-proteins (AGPs), important signalling molecules of land plants, are present in seagrass cell walls is of evolutionary and plant development interest. AGPs of Zostera marina L. were isolated and structurally characterised by analytical and bioinformatics methods as well as by ELISA with different anti-AGP antibodies. Calcium-binding capacity of AGPs was studied by isothermal titration calorimetry (ITC) and microscopy. Bioinformatic searches of the Z. marina proteome identified 9 classical AGPs and a large number of chimeric AGPs. The glycan structures exhibit unique features, including a high degree of branching and an unusually high content of terminating 4-O-methyl-glucuronic acid (4-OMe GlcA) residues. Although the common backbone structure of land plant AGPs is conserved in Z. marina, the terminating residues are distinct with high amounts of uronic acids. These differences likely result from the glycan-active enzymes (glycosyltransferases and methyltransferases) and are essential for calcium-binding properties. The role of this polyanionic surface is discussed with regard to adaption to the marine environment.

The Proline-Rich Family Protein EXTENSIN33 Is Required for Etiolated Arabidopsis thaliana Hypocotyl Growth.

Growth of etiolated Arabidopsis hypocotyls is biphasic. During the first phase, cells elongate slowly and synchronously. At 48 h after imbibition, cells at the hypocotyl base accelerate their growth. Subsequently, this rapid elongation propagates through the hypocotyl from base to top. It is largely unclear what regulates the switch from slow to fast elongation. Reverse genetics-based screening for hypocotyl phenotypes identified three independent mutant lines of At1g70990, a short extensin (EXT) family protein that we named EXT33, with shorter etiolated hypocotyls during the slow elongation phase. However, at 72 h after imbibition, these dark-grown mutant hypocotyls start to elongate faster than the wild type (WT). As a result, fully mature 8-day-old dark-grown hypocotyls were significantly longer than WTs. Mutant roots showed no growth phenotype. In line with these results, analysis of native promoter-driven transcriptional fusion lines revealed that, in dark-grown hypocotyls, expression occurred in the epidermis and cortex and that it was strongest in the growing part. Confocal and spinning disk microscopy on C-terminal protein-GFP fusion lines localized the EXT33-protein to the ER and cell wall. Fourier-transform infrared microspectroscopy identified subtle changes in cell wall composition between WT and the mutant, reflecting altered cell wall biomechanics measured by constant load extensometry. Our results indicate that the EXT33 short EXT family protein is required during the first phase of dark-grown hypocotyl elongation and that it regulates the moment and extent of the growth acceleration by modulating cell wall extensibility.

The Cell Wall Integrity Pathway Contributes to the Early Stages of Aspergillus fumigatus Asexual Development.

Aspergillus fumigatus is a major cause of human disease. The survival of this fungus is dependent on the cell wall organization and function of its components. The cell wall integrity pathway (CWIP) is the primary signaling cascade that controls de novo synthesis of the cell wall in fungi. Abundant conidiation is a hallmark in A. fumigatus, and uptake of conidia by a susceptible host is usually the initial event in infection. The formation of conidia is mediated by the development of fungus-specific specialized structures, conidiophores, which are accompanied by cell wall remodeling. The molecular regulation of these changes in cell wall composition required for the rise of conidiophore from the solid surface and to disperse the conidia into the air is currently unknown. Here, we investigated the role of CWIP in conidiation. We show that CWIP pkcAG579R, ΔmpkA, and ΔrlmA mutants displayed reduced conidiation during synchronized asexual differentiation. The transcription factor RlmA directly regulated the expression of regulators of conidiation, including flbB, flbC, brlA, abaA, and rasB, as well as genes involved in cell wall synthesis and remodeling, and this affected the chitin content in aerial hyphae. Phosphorylation of RlmA and MpkA was increased during asexual differentiation. We also observed that MpkA physically associated with the proteins FlbB, FlbC, BrlA, and RasB during this process, suggesting another level of cross talk between the CWIP and asexual development pathways. In summary, our results support the conclusion that one function of the CWIP is the regulation of asexual development in filamentous fungi.IMPORTANCE A remarkable feature of the human pathogen Aspergillus fumigatus is its ability to produce impressive amounts of infectious propagules known as conidia. These particles reach immunocompromised patients and may initiate a life-threatening mycosis. The conidiation process in Aspergillus is governed by a sequence of proteins that coordinate the development of conidiophores. This process requires the remodeling of the cell wall so that the conidiophores can rise and withstand the chains of conidia. The events regulating cell wall remodeling during conidiation are currently unknown. Here, we show that the cell wall integrity pathway (CWIP) components RlmA and MpkA directly contribute to the activation of the conidiation cascade by enabling transcription or phosphorylation of critical proteins involved in asexual development. This study points to an essential role for the CWIP during conidiation and provides further insights into the complex regulation of asexual development in filamentous fungi.