Suberin deposition in potato periderm: a novel resistance mechanism against tuber greening

PaMYB11 promotes suberin deposition in Norway spruce embryogenic tissue during cryopreservation: A novel resistance mechanism against osmosis

The osmotic resistance mechanism has been extensively studied in whole plants or plant tissues. However, little is known about it in embryogenic tissue (ET) which is widely used in plant-based biotechnological systems. Suberin, a cell wall aliphatic and aromatic heteropolymer, plays a critical role in plant cells against osmosis stress. The suberin regulatory biosynthesis has rarely been studied in gymnosperms. Here, PaMYB11, a subgroup 11 R2R3-MYB transcription factor, plays a key role in the osmotic resistance of Norway spruce (Picea abies) ETs during cryoprotectant pretreatment. Thus, RNA-seq, histological, and analytical chemical analyses are performed on the stable transformations of PaMYB11-OE and PaMYB11-SRDX in Norway spruce ETs. DAP-seq, Y1H, and LUC are further combined to explore the PaMYB11 targets. Activation of PaMYB11 is necessary and sufficient for suberin lamellae deposition on Norway spruce embryogenic cell walls, which plays a decisive role in ET survival under osmotic stress. Transcriptome analysis shows that PaMYB11 enhances suberin lamellae monomer synthesis by promoting very long-chain fatty acid (VLCFA) synthesis. PaPOP, PaADH1, and PaTET8L, the first two (PaADH1 and PaPOP, included) involved in VLCFA synthesis, are proved to be the direct targets of PaMYB11. Our study identified a novel osmotic response directed by PaMYB11 in Norway spruce ET, which provides a new understanding of the resistance mechanism against osmosis in gymnosperms.

Imaging plant cell walls using fluorescent stains: The beauty is in the details

Plants continuously face various environmental stressors throughout their lifetime. To be able to grow and adapt in different environments, they developed specialized tissues that allowed them to maintain a protected yet interconnected body. These tissues undergo specific primary and secondary cell wall modifications that are essential to ensure normal plant growth, adaptation and successful land colonization. The composition of cell walls can vary among different plant species, organs and tissues. The ability to remodel their cell walls is fundamental for plants to be able to cope with multiple biotic and abiotic stressors. A better understanding of the changes taking place in plant cell walls may help identify and develop new strategies as well as tools to enhance plants' survival under environmental stresses or prevent pathogen attack. Since the invention of microscopy, numerous imaging techniques have been developed to determine the composition and dynamics of plant cell walls during normal growth and in response to environmental stimuli. In this review, we discuss the main advances in imaging plant cell walls, with a particular focus on fluorescent stains for different cell wall components and their compatibility with tissue clearing techniques. Lay Description: Plants are continuously subjected to various environmental stresses during their lifespan. They evolved specialized tissues that thrive in different environments, enabling them to maintain a protected yet interconnected body. Such tissues undergo distinct primary and secondary cell wall alterations essential to normal plant growth, their adaptability and successful land colonization. Cell wall composition may differ among various plant species, organs and even tissues. To deal with various biotic and abiotic stresses, plants must have the capacity to remodel their cell walls. Gaining insight into changes that take place in plant cell walls will help identify and create novel tools and strategies to improve plants' ability to withstand environmental challenges. Multiple imaging techniques have been developed since the introduction of microscopy to analyse the composition and dynamics of plant cell walls during growth and in response to environmental changes. Advancements in plant tissue cleaning procedures and their compatibility with cell wall stains have significantly enhanced our ability to perform high-resolution cell wall imaging. At the same time, several factors influence the effectiveness of cleaning and staining plant specimens, as well as the time necessary for the process, including the specimen's size, thickness, tissue complexity and the presence of autofluorescence. In this review, we will discuss the major advances in imaging plant cell walls, with a particular emphasis on fluorescent stains for diverse cell wall components and their compatibility with tissue clearing techniques. We hope that this review will assist readers in selecting the most appropriate stain or combination of stains to highlight specific cell wall components of interest.

Ethanol fumigation combined with modified atmosphere packaging delays potato greening under light

Potato greening under light causes post-harvest loss and compromises progress being made in the potato industry. In this study, we investigated the inhibiting effects of ethanol fumigation treatment on potato greening and water loss under light. This paper also examined the different treatments on the relationship between starch granule size and potato greening. Our results suggested that ethanol fumigation combined with modified atmosphere packaging have an effective in improving the overall visual quality and maintained a higher a* value and lower chlorophyll concentration. Ethanol fumigation combined with modified atmosphere packaging treatment deterred greening and water loss compared to the alone treatment. This was due to the larger starch granule size and fewer grana lamellae around the amyloplasts. Our results provide an effectively strategy that treating potatoes with 600 μL L-1 ethanol combined with modified atmosphere packaging to delay potato greening and explain the underlying mechanism of ethanol inhibition of potato greening.

PpyMYB144 transcriptionally regulates pear fruit skin russeting by activating the cytochrome P450 gene PpyCYP86B1

PpyMYB144 directly activates the promoter of PpyCYP86B1, promotes the synthesis of α, ω-diacids, and involves in pear fruit skin russeting. Russeting is an economically important surface disorder in pear (Pyrus pyrifolia) fruit. Previous research has demonstrated that suberin is the pivotal chemical component contributing to pear fruit skin russeting, and fruit bagging treatment effectively reduces the amount of suberin of fruits, and thereby reduces the russeting phenotype. However, the mechanisms of pear fruit skin russeting remain largely unclear, particularly the transcriptional regulation. Here, we dissected suberin concentration and composition of pear fruits along fruit development and confirmed that α, ω-diacids are the predominant constituents in russeted pear fruit skins. Two cytochrome P450 monooxygenase (CYP) family genes (PpyCYP86A1 and PpyCYP86B1) and nine MYB genes were isolated from pear fruit. Expressions of PpyCYP86A1, PpyCYP86B1, and five MYB genes (PpyMYB34, PpyMYB138, PpyMYB138-like, PpyMYB139, and PpyMYB144) were up-regulated during fruit russeting and showed significant correlations with the changes of α, ω-diacids. In addition, dual-luciferase assays indicated that PpyMYB144 could trans-activate the promoter of PpyCYP86B1, and the activation was abolished by motif mutagenesis of AC element on the PpyCYP86B1 promoter. Further, Agrobacterium-mediated transient expression of PpyCYP86B1 and PpyMYB144 in pear fruits induced the deposition of aliphatic suberin. Thus, PpyMYB144 is a novel direct activator of PpyCYP86B1 and contributes to pear fruit skin russeting.

Irrigation Effect on Yield, Skin Blemishes, Phellem Formation, and Total Phenolics of Red Potatoes

Dark Red Norland is an important potato cultivar in the fresh market due to its attractive bright, red colour, and good yield. However, skin blemishes such as silver patch, surface cracking, and russeting can negatively influence the tuber skin quality and marketability. It is well known that potato is a drought-sensitive plant. This study was conducted to determine whether irrigation would affect Dark Red Norland's yield and skin quality. A three-year field trial was conducted by Peak of the Market in Manitoba, Canada. Plants were treated under both irrigation and rainfed conditions. The results show that irrigation increased the total yield by 20.6% and reduced the severity of surface cracking by 48.5%. Microscopy imaging analysis demonstrated that tubers from the rainfed trials formed higher numbers of suberized cell layers than those of the irrigated potatoes, with a difference of 0.360 to 0.652 layers in normal skins. Surface cracking and silver patch skins had more suberized cell layers than the normal skins, with ranges of 7.805 to 8.333 and 7.740 to 8.496, respectively. A significantly higher amount of total polyphenols was found in the irrigated samples with a mean of 77.30 mg gallic acid equivalents (GAE)/100 g fresh weight (fw) than that of the rainfed samples (69.80 mg GAE/100 g fw). The outcome of this study provides a better understanding of the water regime effect causing these skin blemishes, which could potentially be used to establish strategies to improve tuber skin quality and minimize market losses.

Sodium silicate promotes wound healing by inducing the deposition of suberin polyphenolic and lignin in potato tubers

Wound healing is a postharvest characteristic of potato tubers through accumulating suberin and lignin, which could reduce decay and water loss during storage. This study aimed to explore the impact and mechanisms of sodium silicate on wound healing of potatoes. After being wounded, "Atlantic" potato tubers were treated with water or 50 mM sodium silicate. The results showed that sodium silicate treatment accelerated the formation of wound healing structures and significantly reduced the weight loss and disease index of tubers. Furthermore, sodium silicate induced the genes expression and enzyme activity of phenylalanine ammonia lyase (PAL), 4-coumarate: coenzyme A ligase (4CL), and cinnamyl alcohol dehydrogenase (CAD) involved in the phenylpropane metabolism, enhancing the synthesis of the main precursors of suberin polyphenolic (SPP) and lignin, such as coniferyl alcohol, sinapyl alcohol, and cinnamyl alcohol. Meanwhile, the gene expression of StPOD and StNOX was activated, and the production of O^2- and H₂O₂ was promoted, which could be used for injury signal transmission and oxidative crosslinking of SPP monomers and lignin precursors. Besides, antimicrobial compounds, total phenolics, and flavonoids were also induced. We suggest that sodium silicate could promote wound healing by inducing the deposition of SPP, lignin, and antimicrobial compounds in potato tubers.

Arabidopsis transcription factor TCP4 represses chlorophyll biosynthesis to prevent petal greening

Green petals pose a challenge for pollinators to distinguish flowers from leaves, but they are valuable as a specialty flower trait. However, little is understood about the molecular mechanisms that underlie the development of green petals. Here, we report that CINCINNATA (CIN)-like TEOSINTE BRANCHED 1/CYCLOIDEA/PCF (TCP) proteins play key roles in the control of petal color. The septuple tcp2/3/4/5/10/13/17 mutant produced flowers with green petals due to chlorophyll accumulation. Expression of TCP4 complemented the petal phenotype of tcp2/3/4/5/10/13/17. We found that chloroplasts were converted into leucoplasts in the distal parts of wild-type petals but not in the proximal parts during flower development, whereas plastid conversion was compromised in the distal parts of tcp2/3/4/5/10/13/17 petals. TCP4 and most CIN-like TCPs were predominantly expressed in distal petal regions, consistent with the green-white pattern in wild-type petals and the petal greening observed in the distal parts of tcp2/3/4/5/10/13/17 petals. RNA-sequencing data revealed that most chlorophyll biosynthesis genes were downregulated in the white distal parts of wild-type petals, but these genes had elevated expression in the distal green parts of tcp2/3/4/5/10/13/17 petals and the green proximal parts of wild-type petals. We revealed that TCP4 repressed chlorophyll biosynthesis by directly binding to the promoters of PROTOCHLOROPHYLLIDE REDUCTASE (PORB), DIVINYL REDUCTASE (DVR), and SUPPRESSOR OF OVEREXPRESSION OF CO 1 (SOC1), which are known to promote petal greening. We found that the conversion of chloroplasts to leucoplasts and the green coloration in the proximal parts of petals appeared to be conserved among plant species. Our findings uncover a major molecular mechanism that underpins the formation of petal color patterns and provide a foundation for the breeding of plants with green flowers.

The Making of Plant Armor: The Periderm

The periderm acts as armor protecting the plant's inner tissues from biotic and abiotic stress. It forms during the radial thickening of plant organs such as stems and roots and replaces the function of primary protective tissues such as the epidermis and the endodermis. A wound periderm also forms to heal and protect injured tissues. The periderm comprises a meristematic tissue called the phellogen, or cork cambium, and its derivatives: the lignosuberized phellem and the phelloderm. Research on the periderm has mainly focused on the chemical composition of the phellem due to its relevance as a raw material for industrial processes. Today, there is increasing interest in the regulatory network underlying periderm development as a novel breeding trait to improve plant resilience and to sequester CO₂. Here, we discuss our current understanding of periderm formation, focusing on aspects of periderm evolution, mechanisms of periderm ontogenesis, regulatory networks underlying phellogen initiation and cork differentiation, and future challenges of periderm research.

Suberin Biosynthesis, Assembly, and Regulation

Suberin is a specialized cell wall modifying polymer comprising both phenolic-derived and fatty acid-derived monomers, which is deposited in below-ground dermal tissues (epidermis, endodermis, periderm) and above-ground periderm (i.e., bark). Suberized cells are largely impermeable to water and provide a critical protective layer preventing water loss and pathogen infection. The deposition of suberin is part of the skin maturation process of important tuber crops such as potato and can affect storage longevity. Historically, the term "suberin" has been used to describe a polyester of largely aliphatic monomers (fatty acids, ω-hydroxy fatty acids, α,ω-dioic acids, 1-alkanols), hydroxycinnamic acids, and glycerol. However, exhaustive alkaline hydrolysis, which removes esterified aliphatics and phenolics from suberized tissue, reveals a core poly(phenolic) macromolecule, the depolymerization of which yields phenolics not found in the aliphatic polyester. Time course analysis of suberin deposition, at both the transcriptional and metabolite levels, supports a temporal regulation of suberin deposition, with phenolics being polymerized into a poly(phenolic) domain in advance of the bulk of the poly(aliphatics) that characterize suberized cells. In the present review, we summarize the literature describing suberin monomer biosynthesis and speculate on aspects of suberin assembly. In addition, we highlight recent advances in our understanding of how suberization may be regulated, including at the phytohormone, transcription factor, and protein scaffold levels.

BdFAR4, a root-specific fatty acyl-coenzyme A reductase, is involved in fatty alcohol synthesis of root suberin polyester in Brachypodium distachyon

Suberin is a complex hydrophobic polymer of aliphatic and phenolic compounds which controls the movement of gases, water, and solutes and protects plants from environmental stresses and pathogenic infection. The synthesis and regulatory pathways of suberin remain unknown in Brachypodium distachyon. Here we describe the identification of a B. distachyon gene, BdFAR4, encoding a fatty acyl-coenzyme A reductase (FAR) by a reverse genetic approach, and investigate the molecular relevance of BdFAR4 in the root suberin synthesis of B. distachyon. BdFAR4 is specifically expressed throughout root development. Heterologous expression of BdFAR4 in yeast (Saccharomyces cerevisiae) afforded the production of C20:0 and C22:0 fatty alcohols. The loss-of-function knockout of BdFAR4 by CRISPR/Cas9-mediated gene editing significantly reduced the content of C20:0 and C22:0 fatty alcohols associated with root suberin. In contrast, overexpression of BdFAR4 in B. distachyon and tomato (Solanum lycopersicum) resulted in the accumulation of root suberin-associated C20:0 and C22:0 fatty alcohols, suggesting that BdFAR4 preferentially accepts C20:0 and C22:0 fatty acyl-CoAs as substrates. The BdFAR4 protein was localized to the endoplasmic reticulum in Arabidopsis thaliana protoplasts and Nicotiana benthamiana leaf epidermal cells. BdFAR4 transcript levels can be increased by abiotic stresses and abscisic acid treatment. Furthermore, yeast one-hybrid, dual-luciferase activity, and electrophoretic mobility shift assays indicated that the R2R3-MYB transcription factor BdMYB41 directly binds to the promoter of BdFAR4. Taken together, these results imply that BdFAR4 is essential for the production of root suberin-associated fatty alcohols, especially under stress conditions, and that its activity is transcriptionally regulated by the BdMYB41 transcription factor.

Quantifying risk factors associated with light-induced potato tuber greening in retail stores

Light conditions in retail stores may contribute to potato greening. In this study, we aimed to develop a potato tuber greening risk rating model for retail stores based on light quality and intensity parameters. This was achieved by firstly exposing three potato varieties (Nicola, Maranca and Kennebec) to seven specific light wavelengths (370, 420, 450, 530, 630, 660 and 735 nm) to determine the tuber greening propensity. Detailed light quality and intensity measurements from 25 retail stores were then combined with the greening propensity data to develop a tuber greening risk rating model. Our study showed that maximum greening occurred under blue light (450 nm), while 53%, 65% and 75% less occurred under green (530 nm), red (660 nm) and orange (630 nm) light, respectively. Greening risk, which varied between stores, was found to be related to light intensity level, and partially explained potato stock loss in stores. Our results from this study suggested that other in-store management practices, including lighting duration, average potato turnover, and light protection during non-retail periods, likely influence tuber greening risk.