Ultra-Low Oxygen and Preconditioning Storage Regulate Ethylene Synthesis to Prevent Corky Disorders in 'Fuji' Apple.

Corky disorders in apples represent a significant problem for long-term storage where controlled atmosphere (CA) is mainly used. Ultra-low oxygen (ULO) is an alternative to CA, which consists of low partial pressure of O2 to maintain a low metabolism in the apple fruit, achieving an effective decrease in the ethylene production and physiological disorders. The aim of this research was to study the effectiveness of a short hypoxia period on the development of cork physiological disorders during the storage of apple. 'Fuji' apples were prestored under ULO (0.5 kPa O2) for two periods of time (15 and 30 days) and at two temperatures (0 or 5°C). Corky physiological disorders increased at 5°C prestorage temperature; however, ULO treatments for 15 or 30 days at 0 or 5°C achieved a significant reduction in corky disorders near to 1%, compared with control treatments. In addition, a considerable reduction in ethylene production for up to 30 days was observed in ULO-treated fruit at 0 and 5°C. ULO for 30 days at 0 and 5°C increased the internal production of ethanol and acetaldehyde, causing a lower sensory quality due to the presence of fermentative flavors in fruit stored at 5°C. ULO of 15 days of conditioning decreased the relative expression of ethylene biosynthesis genes MdACS1 and MdACO1, resulting in lower ethylene production.

Low Salt Treatment Results in Plant Growth Enhancement in Tomato Seedlings.

Climate change together with excessive fertilization and poor water quality can affect soil quality and salinization. In plants, high salinity causes osmotic stress, ionic toxicity, and oxidative stress. Consequently, salt stress limits plant development, growth, productivity, and yield. Tomatoes are a very common agricultural product, and some cultivars can partially tolerate salinity. However, most studies are focused on salt excess, which does not necessarily extrapolate on how plants develop in soils with low concentrations of salts. Thus, this study characterizes plant growth and the development of different salt concentrations from 25 to 200 mM in Solanum lycopersicum cv. Moneymaker. Tomato seedlings grown in Murashige and Skoog medium supplied with different NaCl concentrations (0, 25, 50, 75, 100, 125, 150, 175, and 200 mM) showed that low salt concentrations (25 and 50 mM) have a positive impact on lateral root development. This was further observed in physiological parameters such as shoot length, primary root length, and proliferation of lateral roots versus controls. Interestingly, no significant changes in Na+ concentration were observed in 25 mM NaCl in roots or shoots versus controls. Overall, our results suggest that non-toxic salt concentrations can have a positive impact on plant development.

Wine astringency: more than just tannin-protein interactions.

Red wines are characterized by their astringency, a very important sensory attribute that affects the perceived quality of wines. Three mechanisms have been proposed to explain astringency, and two theories describe how these mechanisms work in an integrated manner to produce tactile sensations such as drying, roughening, shrinking and puckering. The factors involved include not only tannins and salivary proteins, but also anthocyanins, grape polysaccharides and mannoproteins, as well as other wine matrix components that modulate their interactions. These multifactorial interactions could be responsible for different sensory responses and therefore need to be further studied. This review presents the latest advances in astringency perception and its possible origins, with special attention on the interactions of components, their impact on oral perception and the development of astringency sub-qualities. Future research efforts should concentrate on understanding the mechanisms involved as well as on the limiting factors related to the conformation and stability of the tannin-salivary protein complexes. © 2021 Society of Chemical Industry.

Stable Transformation of Arabidopsis thaliana Cell Suspension Cultures: A Case Study for The Overexpression of the COI1 Receptor.

Cell suspension cultures have been studied for decades to produce natural molecules. However, the difficulty in generating stably transformed cell lines has limited their use to produce high value chemicals reproducibly and in elevated quantities. In this protocol, a method to stably transform and maintain Arabidopsis cell suspension cultures is devised and presented in detail. Arabidopsis cell cultures were directly transformed with A. tumefaciens for the overexpression of the CORONATINE INSENSITIVE 1 (COI1) jasmonate receptor. Cell cultures were established after transformation and continuously maintained and tested for the overexpression of COI1. The protocol was also previously used to silence Arabidopsis peroxidases and allows for long term maintenance of transformed cells. Details on culture maintenance, both in liquid and solid media are provided, alongside with evidence of protein expression to confirm transformation. The system described provides a powerful tool for synthetic biology to study signaling independent of developmental control and to obtain metabolites of interest for the biotechnological and medical sectors.

Local Changes in Chromatin Accessibility and Transcriptional Networks Underlying the Nitrate Response in Arabidopsis Roots.

Transcriptional regulation, determined by the chromatin structure and regulatory elements interacting at promoter regions, is a key step in plant responses to environmental cues. Nitrate (NO3-) is a nutrient signal that regulates the expression of hundreds of genes in Arabidopsis thaliana. Here, we integrate mRNA sequencing, genome-wide RNA polymerase II (RNPII), chromatin immunoprecipitation sequencing, and DNase sequencing datasets to establish the relationship between RNPII occupancy and chromatin accessibility in response to NO3- treatments in Arabidopsis roots. Genomic footprinting allowed us to identify in vivo regulatory elements controlling gene expression in response to NO3- treatments. NO3--modulated transcription factor (TF) footprints are important for a rapid increase in RNPII occupancy and transcript accumulation over time. We mapped key TF regulatory interactions and functionally validated the role of NAP, an NAC-domain containing TF, as a new regulatory factor in NO3- transport. Taken together, our study provides a comprehensive view of transcriptional networks in response to a nutrient signal in Arabidopsis roots.

COI1-dependent jasmonate signalling affects growth, metabolite production and cell wall protein composition in arabidopsis.

Background and Aims: Cultured cell suspensions have been the preferred model to study the apoplast as well as to monitor metabolic and cell cycle-related changes. Previous work showed that methyl jasmonate (MeJA) inhibits leaf growth in a CORONATINE INSENSITIVE 1 (COI1)-dependent manner, with COI1 being the jasmonate (JA) receptor. Here, the effect of COI1 overexpression on the growth of stably transformed arabidopsis cell cultures is described. Methods: Time-course experiments were carried out to analyse gene expression, and protein and metabolite levels. Key Results: Both MeJA treatment and the overexpression of COI1 modify growth, by altering cell proliferation and expansion. DNA content as well as transcript patterns of cell cycle and cell wall remodelling markers were altered. COI1 overexpression also increases the protein levels of OLIGOGALACTURONIDE OXIDASE 1, BETA-GLUCOSIDASE/ENDOGLUCANASES and POLYGALACTURONASE INHIBITING PROTEIN2, reinforcing the role of COI1 in mediating defence responses and highlighting a link between cell wall loosening and growth regulation. Moreover, changes in the levels of the primary metabolites alanine, serine and succinic acid of MeJA-treated Arabidopsis cell cultures were observed. In addition, COI1 overexpression positively affects the availability of metabolites such as ß-alanine, threonic acid, putrescine, glucose and myo-inositol, thereby providing a connection between JA-inhibited growth and stress responses. Conclusions: This study contributes to the understanding of the regulation of growth and the production of metabolic resources by JAs and COI1. This will have important implications in dissecting the complex relationships between hormonal and cell wall signalling in plants. The work also provides tools to uncover novel mechanisms co-ordinating cell division and post-mitotic cell expansion in the absence of organ developmental control.

Nitrate Transport, Sensing, and Responses in Plants.

Nitrogen (N) is an essential macronutrient that affects plant growth and development. N is an important component of chlorophyll, amino acids, nucleic acids, and secondary metabolites. Nitrate is one of the most abundant N sources in the soil. Because nitrate and other N nutrients are often limiting, plants have developed sophisticated mechanisms to ensure adequate supply of nutrients in a variable environment. Nitrate is absorbed in the root and mobilized to other organs by nitrate transporters. Nitrate sensing activates signaling pathways that impinge upon molecular, metabolic, physiological, and developmental responses locally and at the whole plant level. With the advent of genomics technologies and genetic tools, important advances in our understanding of nitrate and other N nutrient responses have been achieved in the past decade. Furthermore, techniques that take advantage of natural polymorphisms present in divergent individuals from a single species have been essential in uncovering new components. However, there are still gaps in our understanding of how nitrate signaling affects biological processes in plants. Moreover, we still lack an integrated view of how all the regulatory factors identified interact or crosstalk to orchestrate the myriad N responses plants typically exhibit. In this review, we provide an updated overview of mechanisms by which nitrate is sensed and transported throughout the plant. We discuss signaling components and how nitrate sensing crosstalks with hormonal pathways for developmental responses locally and globally in the plant. Understanding how nitrate impacts on plant metabolism, physiology, and growth and development in plants is key to improving crops for sustainable agriculture.

Cytokinin cross-talking during biotic and abiotic stress responses.

As sessile organisms, plants have to be able to adapt to a continuously changing environment. Plants that perceive some of these changes as stress signals activate signaling pathways to modulate their development and to enable them to survive. The complex responses to environmental cues are to a large extent mediated by plant hormones that together orchestrate the final plant response. The phytohormone cytokinin is involved in many plant developmental processes. Recently, it has been established that cytokinin plays an important role in stress responses, but does not act alone. Indeed, the hormonal control of plant development and stress adaptation is the outcome of a complex network of multiple synergistic and antagonistic interactions between various hormones. Here, we review the recent findings on the cytokinin function as part of this hormonal network. We focus on the importance of the crosstalk between cytokinin and other hormones, such as abscisic acid, jasmonate, salicylic acid, ethylene, and auxin in the modulation of plant development and stress adaptation. Finally, the impact of the current research in the biotechnological industry will be discussed.

Reactive oxygen species and their role in plant defence and cell wall metabolism.

Harnessing the toxic properties of reactive oxygen species (ROS) to fight off invading pathogens can be considered a major evolutionary success story. All aerobic organisms have evolved the ability to regulate the levels of these toxic intermediates, whereas some have evolved elaborate signalling pathways to dramatically increase the levels of ROS and use them as weapons in mounting a defence response, a process commonly referred to as the oxidative burst. The balance between steady state levels of ROS and the exponential increase in these levels during the oxidative burst has begun to shed light on complex signalling networks mediated by these molecules. Here, we discuss the different sources of ROS that are present in plant cells and review their role in the oxidative burst. We further describe two well-studied ROS generating systems, the NADPH oxidase and apoplastic peroxidase proteins, and their role as the primary producers of ROS during pathogen invasion. We then discuss what is known about the metabolic and proteomic fluxes that occur in plant cells during the oxidative burst and after pathogen recognition, and try to highlight underlying biochemical processes that may provide more insight on the complex regulation of ROS in plants.

A peroxidase-dependent apoplastic oxidative burst in cultured Arabidopsis cells functions in MAMP-elicited defense.

Perception by plants of so-called microbe-associated molecular patterns (MAMPs) such as bacterial flagellin, referred to as pattern-triggered immunity, triggers a rapid transient accumulation of reactive oxygen species (ROS). We previously identified two cell wall peroxidases, PRX33 and PRX34, involved in apoplastic hydrogen peroxide (H2O2) production in Arabidopsis (Arabidopsis thaliana). Here, we describe the generation of Arabidopsis tissue culture lines in which the expression of PRX33 and PRX34 is knocked down by antisense expression of a heterologous French bean (Phaseolus vulgaris) peroxidase cDNA construct. Using these tissue culture lines and two inhibitors of ROS generation, azide and diphenylene iodonium, we found that perxoxidases generate about half of the H2O2 that accumulated in response to MAMP treatment and that NADPH oxidases and other sources such as mitochondria account for the remainder of the ROS. Knockdown of PRX33/PRX34 resulted in decreased expression of several MAMP-elicited genes, including MYB51, CYP79B2, and CYP81F2. Similarly, proteomic analysis showed that knockdown of PRX33/PRX34 led to the depletion of various MAMP-elicited defense-related proteins, including the two cysteine-rich peptides PDF2.2 and PDF2.3. Knockdown of PRX33/PRX34 also led to changes in the cell wall proteome, including increases in enzymes involved in cell wall remodeling, which may reflect enhanced cell wall expansion as a consequence of reduced H2O2-mediated cell wall cross-linking. Comparative metabolite profiling of a CaCl2 extract of the PRX33/PRX34 knockdown lines showed significant changes in amino acids, aldehydes, and keto acids but not fatty acids and sugars. Overall, these data suggest that PRX33/PRX34-generated ROS production is involved in the orchestration of pattern-triggered immunity in tissue culture cells.

The apoplastic oxidative burst peroxidase in Arabidopsis is a major component of pattern-triggered immunity.

In plants, reactive oxygen species (ROS) associated with the response to pathogen attack are generated by NADPH oxidases or apoplastic peroxidases. Antisense expression of a heterologous French bean (Phaseolus vulgaris) peroxidase (FBP1) cDNA in Arabidopsis thaliana was previously shown to diminish the expression of two Arabidopsis peroxidases (peroxidase 33 [PRX33] and PRX34), block the oxidative burst in response to a fungal elicitor, and cause enhanced susceptibility to a broad range of fungal and bacterial pathogens. Here we show that mature leaves of T-DNA insertion lines with diminished expression of PRX33 and PRX34 exhibit reduced ROS and callose deposition in response to microbe-associated molecular patterns (MAMPs), including the synthetic peptides Flg22 and Elf26 corresponding to bacterial flagellin and elongation factor Tu, respectively. PRX33 and PRX34 knockdown lines also exhibited diminished activation of Flg22-activated genes after Flg22 treatment. These MAMP-activated genes were also downregulated in unchallenged leaves of the peroxidase knockdown lines, suggesting that a low level of apoplastic ROS production may be required to preprime basal resistance. Finally, the PRX33 knockdown line is more susceptible to Pseudomonas syringae than wild-type plants. In aggregate, these data demonstrate that the peroxidase-dependent oxidative burst plays an important role in Arabidopsis basal resistance mediated by the recognition of MAMPs.

Detection of Hydrogen Peroxide by DAB Staining in Arabidopsis Leaves.

In this protocol, the in situ detection of hydrogen peroxide (one of several reactive oxygen species) is described in mature Arabidopsis rosette leaves by staining with 3,3'-diaminobenzidine (DAB) using an adaptation of previous methods (Thordal-Christensen et al., 1997; Bindschedler et al., 2006; Daudi et al., 2012). DAB is oxidized by hydrogen peroxide in the presence of some haem-containing proteins, such as peroxidases, to generate a dark brown precipitate. This precipitate is exploited as a stain to detect the presence and distribution of hydrogen peroxide in plant cells. The protocol can be modified slightly to detect hydrogen peroxide in different types of plant tissue.