PHYTOALEXIN DEFICIENT 4 affects reactive oxygen species metabolism, cell wall and wood properties in hybrid aspen (Populus tremula L. × tremuloides)

Biotechnological Potential of the Stress Response and Plant Cell Death Regulators Proteins in the Biofuel Industry

Production of biofuel from lignocellulosic biomass is relatively low due to the limited knowledge about natural cell wall loosening and cellulolytic processes in plants. Industrial separation of cellulose fiber mass from lignin, its saccharification and alcoholic fermentation is still cost-ineffective and environmentally unfriendly. Assuming that the green transformation is inevitable and that new sources of raw materials for biofuels are needed, we decided to study cell death-a natural process occurring in plants in the context of reducing the recalcitrance of lignocellulose for the production of second-generation bioethanol. "Members of the enzyme families responsible for lysigenous aerenchyma formation were identified during the root hypoxia stress in Arabidopsis thaliana cell death mutants. The cell death regulatory genes, LESION SIMULATING DISEASE 1 (LSD1), PHYTOALEXIN DEFICIENT 4 (PAD4) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) conditionally regulate the cell wall when suppressed in transgenic aspen. During four years of growth in the field, the following effects were observed: lignin content was reduced, the cellulose fiber polymerization degree increased and the growth itself was unaffected. The wood of transgenic trees was more efficient as a substrate for saccharification, alcoholic fermentation and bioethanol production. The presented results may trigger the development of novel biotechnologies in the biofuel industry.

Mitochondrial HSC70-1 Regulates Polar Auxin Transport through ROS Homeostasis in Arabidopsis Roots

Arabidopsis mitochondrial-localized heat shock protein 70-1 (mtHSC70-1) modulates vegetative growth by assisting mitochondrial complex IV assembly and maintaining reactive oxygen species (ROS) homeostasis. In addition, mtHSC70-1 affects embryo development, and this effect is mediated by auxin. However, whether mtHSC70-1 regulates vegetative growth through auxin and knowledge of the link between ROS homeostasis and auxin distribution remain unclear. Here, we found that mtHSC70-1 knockout seedlings (mthsc70-1a) displayed shortened roots, decreased fresh root weight and lateral root number, increased root width and abnormal root morphology. The introduction of the mtHSC70-1 gene into mthsc70-1a restored the growth and development of roots to the level of the wild type. However, sugar and auxin supplementation could not help the mutant roots restore to normal. Moreover, mthsc70-1a seedlings showed a decrease in meristem length and activity, auxin transport carrier (PINs and AUX1) and auxin abundances in root tips. The application of exogenous reducing agents upregulated the levels of PINs in the mutant roots. The introduction of antioxidant enzyme genes (MSD1 or CAT1) into the mthsc70-1a mutant rescued the PIN and local auxin abundances and root growth and development. Taken together, our data suggest that mtHSC70-1 regulates polar auxin transport through ROS homeostasis in Arabidopsis roots.

Foamed Eco-Geopolymer Modified by Perlite and Cellulose as a Construction Material for Energy-Efficient Buildings

Irreversible climate change, including atmosphere temperature extremes, is one of the most important issues of the present time. In this context, the construction industry requires solutions for increasing the energy efficiency of buildings through feedback between temperature adjustment inside buildings and better isolation of the external parts of buildings. Newly developed thermal insulation materials play an important role in this strategy. This paper presents the foamed geopolymer based on metakaolin that can be used as a modern facade material. In order to further improve its thermal insulation properties, the composition of geopolymer was modified with organic substances, i.e., perlite and cellulose fibers (30% and 50% of the volume). The thermal conductivity and insulation properties, density, mineral phases, absorbability, and compressive strength were improved for composite materials. It has been shown that the final properties of the foamed geopolymer can be controlled to a great extent by modifications, and the final properties determine its applicability.

MITOGEN-ACTIVATED PROTEIN KINASE 4 impacts leaf development, temperature, and stomatal movement in hybrid aspen

Stomatal movement and density influence plant water use efficiency and thus biomass production. Studies in model plants within controlled environments suggest MITOGEN-ACTIVATED PROTEIN KINASE 4 (MPK4) may be crucial for stomatal regulation. We present functional analysis of MPK4 for hybrid aspen (Populus tremula × tremuloides) grown under natural field conditions for several seasons. We provide evidence of the role of MPK4 in the genetic and environmental regulation of stomatal formation, differentiation, signaling, and function; control of the photosynthetic and thermal status of leaves; and growth and acclimation responses. The long-term acclimation manifested as variations in stomatal density and distribution. Short-term acclimation responses were derived from changes in the stomatal aperture. MPK4 localized in the cytoplasm of guard cells (GCs) was a positive regulator of abscisic acid (ABA)-dependent stomatal closure and nitric oxide metabolism in the ABA-dependent pathways, while to a lesser extent, it was involved in ABA-induced hydrogen peroxide accumulation. MPK4 also affected the stomatal aperture through deregulation of microtubule patterns and cell wall structure and composition, including via pectin methyl-esterification, and extensin levels in the GC wall. Deregulation of leaf anatomy (cell compaction) and stomatal movement, together with increased light energy absorption, resulted in altered leaf temperature, photosynthesis, cell death, and biomass accumulation in mpk4 transgenic plants. Divergence between absorbed energy and assimilated energy is a bottleneck, and MPK4 can participate in the control of energy dissipation (thermal effects). Furthermore, MPK4 can participate in balancing the photosynthetic energy distribution via its effective use in growth or redirection to acclimation/defense responses.

Programmed cell death (PCD) control in plants: New insights from the Arabidopsis thaliana deathosome

Programmed cell death (PCD) is a genetically controlled process that leads to cell suicide in both eukaryotic and prokaryotic organisms. In plants PCD occurs during development, defence response and when exposed to adverse conditions. PCD acts controlling the number of cells by eliminating damaged, old, or unnecessary cells to maintain cellular homeostasis. Unlike in animals, the knowledge about PCD in plants is limited. The molecular network that controls plant PCD is poorly understood. Here we present a review of the current mechanisms involved with the genetic control of PCD in plants. We also present an updated version of the AtLSD1 deathosome, which was previously proposed as a network controlling HR-mediated cell death in Arabidopsis thaliana. Finally, we discuss the unclear points and open questions related to the AtLSD1 deathosome.

Biotechnological Potential of LSD1, EDS1, and PAD4 in the Improvement of Crops and Industrial Plants

Lesion Simulating Disease 1 (LSD1), Enhanced Disease Susceptibility (EDS1) and Phytoalexin Deficient 4 (PAD4) were discovered a quarter century ago as regulators of programmed cell death and biotic stress responses in Arabidopsis thaliana. Recent studies have demonstrated that these proteins are also required for acclimation responses to various abiotic stresses, such as high light, UV radiation, drought and cold, and that their function is mediated through secondary messengers, such as salicylic acid (SA), reactive oxygen species (ROS), ethylene (ET) and other signaling molecules. Furthermore, LSD1, EDS1 and PAD4 were recently shown to be involved in the modification of cell walls, and the regulation of seed yield, biomass production and water use efficiency. The function of these proteins was not only demonstrated in model plants, such as Arabidopsis thaliana or Nicotiana benthamiana, but also in the woody plant Populus tremula x tremuloides. In addition, orthologs of LSD1, EDS1, and PAD4 were found in other plant species, including different crop species. In this review, we focus on specific LSD1, EDS1 and PAD4 features that make them potentially important for agricultural and industrial use.

LSD1-, EDS1- and PAD4-dependent conditional correlation among salicylic acid, hydrogen peroxide, water use efficiency and seed yield in Arabidopsis thaliana

In Arabidopsis thaliana, LESION SIMULATING DISEASE 1 (LSD1), ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) and PHYTOALEXIN DEFICIENT 4 (PAD4) proteins are regulators of cell death (CD) in response to abiotic and biotic stresses. Hormones, such as salicylic acid (SA), and reactive oxygen species, such as hydrogen peroxide (H₂ O₂ ), are key signaling molecules involved in plant CD. The proposed mathematical models presented in this study suggest that LSD1, EDS1 and PAD4 together with SA and H₂ O₂ are involved in the control of plant water use efficiency (WUE), vegetative growth and generative development. The analysis of Arabidopsis wild-type and single mutants lsd1, eds1, and pad4, as well as double mutants eds1/lsd1 and pad4/lsd1, demonstrated the strong conditional correlation between SA/H₂ O₂ and WUE that is dependent on LSD1, EDS1 and PAD4 proteins. Moreover, we found a strong correlation between the SA/H₂ O₂ homeostasis of 4-week-old Arabidopsis leaves and a total seed yield of 9-week-old plants. Altogether, our results prove that SA and H₂ O₂ are conditionally regulated by LSD1/EDS/PAD4 to govern WUE, biomass accumulation and seed yield. Conditional correlation and the proposed models presented in this study can be used as the starting points in the creation of a plant breeding algorithm that would allow to estimate the seed yield at the initial stage of plant growth, based on WUE, SA and H₂ O₂ content.

Preliminary study of Cell Wall Structure and its Mechanical Properties of C3H and HCT RNAi Transgenic Poplar Sapling

This research focused on the cell wall structure and its mechanical properties of down-regulated Coumaroyl shikimate 3-hydroxylase (C3H) transgenic poplar and down-regulated hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) transgenic poplar (Populus alba × P. glandulosa cv ‘84 k’). The wood samples with respect to microstructure, the longitudinal elastic modulus (MOE) and hardness of wood fiber secondary cell wall were investigated. The results show that the lignin contents in the two transgenic poplar woods were lower than non-modified wood. The C3H transgenic poplar and HCT transgenic poplar have more than 18.5% and 16.1% cellulose crystalline regions than non-modified poplar respectively. The diameter of the fiber cell and the vessel element of transgenic poplars are smaller. Double radial vessel cell wall thicknesses of both transgenic poplars were smaller than non-modified poplar. Cell wall ratios for the transgenic poplar were higher than non-modified poplar and cell wall density was significantly lower in both C3H and HCT transgenic poplar. The cell wall MOEs of C3H and HCT transgenic poplar was 5.8% and 7.0% higher than non-modified poplar. HCT can be more effective than C3H to modify the trees by considerably increasing mechanical properties of the cell wall.

A mongolian pine specific endoplasmic reticulum localized CALMODULIN-LIKE calcium binding protein enhances arabidopsis growth

Stress-adapted wild plants are natural sources of novel genes for molecular breeding. Here, we conducted a transcriptional analysis of Pinus sylvestris var. mongolica Litv, an evergreen pine in northeastern China, to identify a novel CALMODULIN-LIKE protein-encoding gene, PsCML1, no significant homologs found in other plant species. PsCML1 encodes a protein predicted to have a single trans-membrane domain at its N-terminal. Four EF-hand motifs (calcium [Ca]-binding structures) are located at its C-terminal and showed Ca²⁺-specific affinity in isothermal titration calorimetric analysis. Transient expression of PsCML1 in Nicotiana benthamiana showed that the PsCML1 localizes to the endoplasmic reticulum (ER). Heterologous expression of PsCML1 in Arabidopsis significantly promoted seedling growth, and increased resistance to stress from NaCl and Ca²⁺ deficiency. The roots of the transgenic seedlings had higher contents of cellulose and pectin, but less hemicellulose than those of the wild type (WT). The biosynthesis of cell wall components is linked with protein glycosylation in the ER and reactive oxygen species (ROS) homeostasis. No significant difference was found in the extent of protein glycosylation between the transgenic and WT plants. However, the transgenic roots had higher steady-state levels of ROS, NADPH oxidase activity, and endo-membrane dynamics than those of the WT. A working model was proposed to delineate the interaction among Ca²⁺, ROS homeostasis, and cell wall loosening-dependent cell division.

ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) affects development, photosynthesis, and hormonal homeostasis in hybrid aspen (Populus tremula L. × P. tremuloides)

ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) was first described as a protein involved in salicylic acid (SA)-, ethylene-, and reactive oxygen species (ROS)-dependent defense and acclimation responses. It is a molecular regulator of biotic and abiotic stress-induced programmed cell death. Its role is relatively well known in annual plants, such as Arabidopsis thaliana or Nicotiana benthamiana. However, little is known about its functions in woody plants. Therefore, in this study, we aimed to characterize the function of EDS1 in the Populus tremula L. × P. tremuloides hybrid grown for several seasons in the natural environment. We used two transgenic lines, eds1-7 and eds1-12, with decreased EDS1 expression levels in this study. The observed changes in physiological and biochemical parameters corresponded with the EDS1 silencing level. Both transgenic lines produced more lateral shoots in comparison to the wild-type (WT) plants, which resulted in the modification of tree morphology. Photosynthetic parameters, such as quantum yield of photosystem II (ϕPSII), photochemical and non-photochemical quenching (qP and NPQ, respectively), as well as chlorophyll content were found to be increased in both transgenic lines, which resulted in changes in photosynthetic efficiency. Our data also revealed lower foliar concentrations of SA and ROS, the latter resulting most probably from more efficient antioxidant system in both transgenic lines. In addition, our data indicated significantly decreased rate of leaf senescence during several autumn seasons. Transcriptomic analysis revealed deregulation of 2215 and 376 genes in eds1-12 and eds1-7, respectively, and also revealed 207 genes that were commonly deregulated in both transgenic lines. The deregulation was primarily observed in the genes involved in photosynthesis, signaling, hormonal metabolism, and development, which was found to agree with the results of biochemical and physiological tests. In general, our data proved that poplar EDS1 affects tree morphology, photosynthetic efficiency, ROS and SA metabolism, as well as leaf senescence.

Activation of disease resistance against Botryosphaeria dothidea by downregulating the expression of MdSYP121 in apple

In plants, the vesicle fusion process plays a vital role in pathogen defence. However, the importance of the vesicle fusion process in apple ring rot has not been studied. Here, we isolated and characterised the apple syntaxin gene MdSYP121. Silencing the MdSYP121 gene in transgenic apple calli increased tolerance to Botryosphaeria dothidea infection; this increased tolerance was correlated with salicylic acid (SA) synthesis-related and signalling-related gene transcription. In contrast, overexpressing MdSYP121 in apple calli resulted in the opposite phenotypes. In addition, the results of RNA sequencing (RNA-Seq) and quantitative real-time PCR (qRT-PCR) assays suggested that MdSYP121 plays an important role in responses to oxidation-reduction reactions. Silencing MdSYP121 in apple calli enhanced the expression levels of reactive oxygen species (ROS)-related genes and the activity of ROS-related enzymes. The enhanced defence response status in MdSYP121-RNAi lines suggests that syntaxins are involved in the defence response to B. dothidea. More importantly, we showed that MdSYP121 forms a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex with MdSNAP33, and the complex may participate in regulating resistance to B. dothidea. In conclusion, by regulating the interaction of SA pathway and oxidation-reduction process, MdSYP121 can influence the pathogen infection process in apple.