Phospholipase C signaling involvement in macrotubule assembly and activation of the mechanism regulating protoplast volume in plasmolyzed root cells of Triticum turgidum

Genome-wide characterization and expression profiling of the Phospholipase C (PLC) gene family in three orchids of economic importance

Background

Phospholipases hydrolyze glycerophospholipids and generate diverse lipid-derived molecules with secondary messenger activity. Out of these, phospholipase C (PLC) specifically cleaves the phospholipids at ester linkages and yields diacylglycerol (DAG) and phosphorylated head groups. PLCs are classified further as phosphatidylinositol-specific PLCs (PI-PLCs) and non-specific PLCs with biased specificity for phosphatidylcholine (NPC/PC-PLC).

Results

In the present report, we identified and characterized PLC genes in the genomes of three orchids, Phalaenopsis equestris (seven PePLCs), Dendrobium catenatum (eight DcPLCs), and Apostasia shenzhenica (seven AsPLCs). Multiple sequence alignment analysis confirmed the presence of conserved X and Y catalytic domains, calcium/lipid-binding domain (C2 domain) at the C terminal region, and EF-hand at the N-terminal region in PI-PLC proteins and esterase domain in PC-PLC. Systematic phylogenetic analysis established the relationship of the PLC protein sequences and clustered them into two groups (PI-PLC and PC-PLC) along with those of Arabidopsis thaliana and Oryza sativa. Gene architecture studies showed the presence of nine exons in all PI-PLC genes while the number varied from one to five in PC-PLCs. RNA-seq-based spatio-temporal expression profile for PLC genes was generated, which showed that PePC-PLC1, PePC-PLC2A, DcPC-PLC1A, DcPC-PLC1B, DcPC-PLC2, DcPC-PLC1B, and AsPC-PLC1 had significant expression in all reproductive and vegetative tissues. The expression profile is matched to their upstream cis-regulatory promoter elements, which indicates that PLC genes have a role in various growth and development processes and during stress responses.

Conclusions

The present study unwrapped the opportunity for functional characterization of selected PLC genes in planta for plant improvement.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43141-021-00217-z.

The cotton laccase gene GhLAC15 enhances Verticillium wilt resistance via an increase in defence-induced lignification and lignin components in the cell walls of plants

Verticillium dahliae is a phytopathogenic fungal pathogen that causes vascular wilt diseases responsible for considerable decreases in cotton yields. The lignification of cell wall appositions is a conserved basal defence mechanism in the plant innate immune response. However, the function of laccase in defence-induced lignification has not been described. Screening of an SSH library of a resistant cotton cultivar, Jimian20, inoculated with V. dahliae revealed a laccase gene that was strongly induced by the pathogen. This gene was phylogenetically related to AtLAC15 and contained domains conserved by laccases; therefore, we named it GhLAC15. Quantitative reverse transcription-polymerase chain reaction indicated that GhLAC15 maintained higher expression levels in tolerant than in susceptible cultivars. Overexpression of GhLAC15 enhanced cell wall lignification, resulting in increased total lignin, G monolignol and G/S ratio, which significantly improved the Verticillium wilt resistance of transgenic Arabidopsis. In addition, the levels of arabinose and xylose were higher in transgenic plants than in wild-type plants, which resulted in transgenic Arabidopsis plants being less easily hydrolysed. Furthermore, suppression of the transcriptional level of GhLAC15 resulted in an increase in susceptibility in cotton. The content of monolignol and the G/S ratio were lower in silenced cotton plants, which led to resistant cotton cv. Jimian20 becoming susceptible. These results demonstrate that GhLAC15 enhances Verticillium wilt resistance via an increase in defence-induced lignification and arabinose and xylose accumulation in the cell wall of Gossypium hirsutum. This study broadens our knowledge of defence-induced lignification and cell wall modifications as defence mechanisms against V. dahliae.

Genome-Wide Analysis and Expression Profiling of the Phospholipase C Gene Family in Soybean (Glycine max)

Phosphatidylinositol-specific phospholipase C (PI-PLC) hydrolyses phosphatidylinositol-4,5-bisphosphate to produce diacylglycerol and inositol 1,4,5-trisphosphate. It plays an important role in plant development and abiotic stress responses. However, systematic analysis and expression profiling of the phospholipase C (PLC) gene family in soybean have not been reported. In this study, 12 putative PLC genes were identified in the soybean genome. Soybean PLCs were found on chromosomes 2, 11, 14 and 18 and encoded 58.8-70.06 kD proteins. Expression pattern analysis by RT-PCR demonstrated that expression of the GmPLCs was induced by PEG, NaCl and saline-alkali treatments in roots and leaves. GmPLC transcripts accumulated specifically in roots after ABA treatment. Furthermore, GmPLC transcripts were analyzed in various tissues. The results showed that GmPLC7 was highly expressed in most tissues, whereas GmPLC12 was expressed in early pods specifically. In addition, subcellular localization analysis was carried out and confirmed that GmPLC10 was localized in the plasma membrane in Nicotiana benthamiana. Our genomic analysis of the soybean PLC family provides an insight into the regulation of abiotic stress responses and development. It also provides a solid foundation for the functional characterization of the soybean PLC gene family.

Plant phosphoinositide-dependent phospholipases C: variations around a canonical theme

Phosphoinositide-specific phospholipase C (PI-PLC) cleaves, in a Ca(2+)-dependent manner, phosphatidylinositol-4,5-bisphosphate (PI-4,5-P2) into diacylglycerol (DAG) and inositol triphosphate (IP3). PI-PLCs are multidomain proteins that are structurally related to the PI-PLCζs, the simplest animal PI-PLCs. Like these animal counterparts, they are only composed of EF-hand, X/Y and C2 domains. However, plant PI-PLCs do not have a conventional EF-hand domain since they are often truncated, while some PI-PLCs have no EF-hand domain at all. Despite this simple structure, plant PI-PLCs are involved in many essential plant processes, either associated with development or in response to environmental stresses. The action of PI-PLCs relies on the mediators they produce. In plants, IP3 does not seem to be the sole active soluble molecule. Inositol pentakisphosphate (IP5) and inositol hexakisphosphate (IP6) also transmit signals, thus highlighting the importance of coupling PI-PLC action with inositol-phosphate kinases and phosphatases. PI-PLCs also produce a lipid molecule, but plant PI-PLC pathways show a peculiarity in that the active lipid does not appear to be DAG but its phosphorylated form, phosphatidic acid (PA). Besides, PI-PLCs can also act by altering their substrate levels. Taken together, plant PI-PLCs show functional differences when compared to their animal counterparts. However, they act on similar general signalling pathways including calcium homeostasis and cell phosphoproteome. Several important questions remain unanswered. The cross-talk between the soluble and lipid mediators generated by plant PI-PLCs is not understood and how the coupling between PI-PLCs and inositol-kinases or DAG-kinases is carried out remains to be established.

α-tubulin is rapidly phosphorylated in response to hyperosmotic stress in rice and Arabidopsis

By using high-resolution two-dimensional PAGE followed by phosphoprotein-specific staining and peptide mass fingerprint analysis along with other assays, we found that α-tubulin is phosphorylated in response to hyperosmotic stress in rice and Arabidopsis. The onset of the phosphorylation response was as early as 2 min after hyperosmotic stress treatment, and a major proportion of α-tubulin was phosphorylated after 60 min in root tissues. However, the phosphorylated form of α-tubulin was readily dephosphorylated upon stress removal. The phosphorylation site was identified as Thr349 by comprehensive mutagenesis of serine/threonine residues in a rice α-tubulin isoform followed by evaluation in cultured cell protoplasts. This residue is located at the surface for the interaction with β-tubulin in polymerized α-β tubulin dimers and has been proposed to be directly involved in this interaction. Thus, α-tubulin phosphorylation was considered to occur on free tubulin dimers in response to hyperosmotic stress. The incorporation of green fluorescent protein (GFP)-α-tubulin into cortical microtubules was completely inhibited in transgenic Arabidopsis when Thr349 was substituted with glutamate or aspartate. Using transgenic Arabidopsis plants expressing GFP-α-tubulin, we found that hyperosmotic stress causes extensive cortical microtubule depolymerization. Microtubule-destabilizing treatments such as propyzamide or oryzalin and temperature stresses resulted in α-tubulin phosphorylation, whereas hyperosmotic stress-induced α-tubulin phosphorylation was partially inhibited by taxol, which stabilizes microtubules. These results and the three-dimensional location of the phosphorylation site suggested that microtubules are depolymerized in response to hyperosmotic stress via α-tubulin phosphorylation. Together, the results of the present study reveal a novel mechanism that globally regulates the microtubule polymerization.

Disturbance of reactive oxygen species homeostasis induces atypical tubulin polymer formation and affects mitosis in root-tip cells of Triticum turgidum and Arabidopsis thaliana

In this study, the effects of disturbance of the reactive oxygen species (ROS) homeostasis on the organization of tubulin cytoskeleton in interphase and mitotic root-tip cells of Triticum turgidum and Arabidopsis thaliana were investigated. Reduced ROS levels were obtained by treatment with diphenylene iodonium (DPI) and N-acetyl-cysteine, whereas menadione was applied to achieve ROS overproduction. Both increased and low ROS levels induced: (a) Macrotubule formation in cells with low ROS levels and tubulin paracrystals under oxidative stress. The protein MAP65-1 was detected in treated cells, exhibiting a conformation comparable to that of the atypical tubulin polymers. (b) Disappearance of microtubules (MTs). (c) Inhibition of preprophase band formation. (d) Delay of the nuclear envelope breakdown at prometaphase. (e) Prevention of perinuclear tubulin polymer assembly in prophase cells. (f) Loss of bipolarity of prophase, metaphase and anaphase spindles. Interestingly, examination of the A. thaliana rhd2/At respiratory burst oxidase homolog C (rbohc) NADPH oxidase mutant, lacking RHD2/AtRBOHC, gave comparable results. Similarly to DPI, the decreased ROS levels in rhd2 root-tip cells, interfered with MT organization and induced macrotubule assembly. These data indicate, for first time in plants, that ROS are definitely implicated in: (a) mechanisms controlling the assembly/disassembly of interphase, preprophase and mitotic MT systems and (b) mitotic spindle function. The probable mechanisms, by which ROS affect these processes, are discussed.

Desiccation tolerance mechanism in resurrection fern-ally Selaginella tamariscina revealed by physiological and proteomic analysis

Drought is one of the most severe limitations to plant growth and productivity. Resurrection plants have evolved a unique capability to tolerate desiccation in vegetative tissues. Fern-ally Selaginella tamariscina (Beauv.) is one of the most primitive vascular resurrection plants, which can survive a desiccated state and recover when water becomes available. To better understand the mechanism of desiccation tolerance, we have applied physiological and proteomic analysis. Samples of S. tamariscina were water-deprived for up to seven days followed by 12 h of rewatering. Our results showed that endogenous abscisic acid (ABA) increased to regulate dehydration-responsive genes/proteins and physiological processes. In the course of dehydration, the contents of osmolytes represented by soluble sugars and proline were increased to maintain cell structure integrity. The activities of four antioxidant enzymes (superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutathione reductase (GR)) also increased. In contrast, both the rate of photosynthesis and the chlorophyll content decreased, and plasma membrane integrity was lost. We identified 138 desiccation-responsive two-dimensional electrophoresis (2-DE) spots, representing 103 unique proteins. Hierarchical clustering analysis revealed that 83% of the proteins were down-regulated upon dehydration. They were mainly involved in photosynthesis, carbohydrate and energy metabolism, stress and defense, protein metabolism, signaling, membrane/transport, cell structure, and cell division. The dynamic expression changes of the desiccation-responsive proteins provide strong evidence that cell structure modification, photosynthesis reduction, antioxidant system activation, and protein post-transcriptional/translational modifications are essential to the poikilochlorophyllous fern-ally S. tamariscina in response to dehydration. In addition, our comparative analysis of dehydration-responsive proteins in vegetative tissues from 19 desiccation tolerant and nontolerant plant species suggests that resurrection S. tamariscina has developed a specific desiccation tolerant mechanism. To our knowledge, this study constitutes the first detailed investigation of the protein complement in fern/fern-allies.

Inhibition of phospholipase C disrupts cytoskeletal organization and gravitropic growth in Arabidopsis roots

The phospholipase protein superfamily plays an important role in hormonal signalling and cellular responses to environmental stimuli. There is also growing evidence for interactions between phospholipases and the cytoskeleton. In this report we used a pharmacological approach to investigate whether inhibiting a member of the phospholipase superfamily, phospholipase C (PLC), affects microtubules and actin microfilaments as well as root growth and morphology of Arabidopsis thaliana seedlings. Inhibiting PLC activity using the aminosteroid U73122 significantly inhibited root elongation and disrupted root morphology in a concentration-dependent manner, with the response being saturated at 5 μM, whereas the inactive analogue U73343 was ineffective. The primary root appeared to lose growth directionality accompanied by root waving and formation of curls. Immunolabelling of roots exposed to increasingly higher U73122 concentrations revealed that the normal transverse arrays of cortical microtubules in the elongation zone became progressively more disorganized or depolymerized, with the disorganization appearing within 1 h of incubation. Likewise, actin microfilament arrays also were disrupted. Inhibiting PLC using an alternative inhibitor, neomycin, caused similar disruptions to both cytoskeletal organization and root morphology. In seedlings gravistimulated by rotating the culture plates by 90°, both U73122 and neomycin disrupted the normal gravitropic growth of roots and etiolated hypocotyls. The effects of PLC inhibitors are therefore consistent with the notion that, as with phospholipases A and D, PLC likewise interacts with the cytoskeleton, alters growth morphology, and is involved in gravitropism.

Exploring the mechanism of Physcomitrella patens desiccation tolerance through a proteomic strategy

The moss Physcomitrella patens has been shown to tolerate abiotic stresses, including salinity, cold, and desiccation. To better understand this plant's mechanism of desiccation tolerance, we have applied cellular and proteomic analyses. Gametophores were desiccated over 1 month to 10% of their original fresh weight. We report that during the course of dehydration, several related processes are set in motion: plasmolysis, chloroplast remodeling, and microtubule depolymerization. Despite the severe desiccation, the membrane system maintains integrity. Through two-dimensional gel electrophoresis and image analysis, we identified 71 proteins as desiccation responsive. Following identification and functional categorization, we found that a majority of the desiccation-responsive proteins were involved in metabolism, cytoskeleton, defense, and signaling. Degradation of cytoskeletal proteins might result in cytoskeletal disassembly and consequent changes in the cell structure. Late embryogenesis abundant proteins and reactive oxygen species-scavenging enzymes are both prominently induced, and they might help to diminish the damage brought by desiccation.

Intercourse between cell wall and cytoplasm exemplified by arabinogalactan proteins and cortical microtubules

How does a plant cell sense and respond to the status of its cell wall? Intercourse between cell wall and cytoplasm has long been supposed to involve arabinogalactan proteins, in part because many of them are anchored to the plasma membrane. Disrupting arabinogalactan proteins has recently been shown to disrupt the array of cortical microtubules present just inside the plasma membrane, implying that microtubules and arabinogalactan proteins interact. In this article, we assess possibilities for how this interaction might be mediated. First, we consider microdomains in the plasma membrane (lipid rafts), which have been alleged to link internal and external regions of the plasma membrane; however, the characteristics and even the existence of these domains remains controversial. Next, we point out that disrupting the synthesis of cellulose also can disrupt microtubules and consider whether arabinogalactan proteins are part of a network linking microtubules and nascent microfibrils. Finally, we outline several signaling cascades that could transmit information from arabinogalactan proteins to microtubules through channels of cellular communication. These diverse possibilities highlight the work that remains to be done before we can understand how plant cells communicate across their membranes.

The involvement of phospholipases C and D in the asymmetric division of subsidiary cell mother cells of Zea mays

In the present study, the involvement of phospholipase C and D (PLC and PLD) pathways in the asymmetric divisions that produce the stomatal complexes of Zea mays was investigated. In particular, the polar organization of microtubules (MTs) and actin filaments (AFs) and the process of asymmetric division were studied in subsidiary cell mother cells (SMCs) treated with PLC and PLD modulators. In SMCs treated with butanol-1 (but-1), which blocks phosphatidic acid (PA) production via PLDs, AF-patch formation laterally to the inducing guard cell mother cell (GMC) and the subsequent asymmetric division were inhibited. In these SMCs, cell division plane determination, as expressed by MT preprophase band (MT-PPB) formation, was not disturbed. Exogenously applied PA partially relieved the but-1 effects on SMCs. In contrast to SMCs, but-1 did not affect the symmetric GMC division. Inhibition of the PLC catalytic activity by neomycin or U73122 resulted in inhibition of asymmetric SMC division, while AF-patch and MT-PPB were organized as in control SMCs. These data show that the PLC and PLD signaling pathways are involved in the transduction and/or perception of the inductive stimulus that is emitted by the GMCs and induces the polar AF organization and asymmetric SMC division. In contrast, division plane determination in SMCs, as expressed by MT-PPB formation, does not depend on PLC and PLD signaling pathways.