Determining the Subcellular Localization of Fluorescently Tagged Proteins Using Protoplasts Extracted from Transiently Transformed Nicotiana benthamiana Leaves

Protoplast transient transformation facilitates subcellular localization and functional analysis of walnut proteins

Walnut (Juglans regia L.), an important contributor to oil production among woody plants, encounters research constraints due to difficulties in the subcellular localization and functional analysis of its proteins. These limitations arise from the protracted fruiting cycle and the absence of a reliable transient gene transformation system and organelle markers. In this study, we established a transient expression system using walnut protoplasts and generated fluorescent-tagged organelle markers, whose localization was validated against Arabidopsis (Arabidopsis thaliana) organelle markers. The versatility of this system was demonstrated through pharmaceutical treatments, confirming its ability to determine the subcellular localization of endogenous proteins. We determined the subcellular localization of walnut oleosin proteins and explored protein-protein interactions through bimolecular fluorescence complementation analysis. We also explored the effects of abscisic acid signaling on oil body morphology and the regulation of walnut WRINKLED1 (JrWRI1) in lipid biosynthesis. Overall, this stable and versatile protoplast-based transient expression system, integrated with walnut organelle markers, enhances the subcellular localization and functional studies of uncharacterized walnut proteins. This advancement accelerates research into walnut gene function and streamlines molecular breeding processes with high-throughput efficiency.

OsWNK9 mitigates salt stress by promoting root growth and stomatal closure in rice

Salinity stress severely affects rice growth and reduces its productivity. With No Lysine Kinases (WNKs) are serine/threonine kinases emerging as potential candidate genes due to their involvement in various abiotic stress tolerance responses. However, studies providing mechanistic insights into the roles of WNKs in plants remain scarce. In the present study, OsWNK9-overexpressing rice lines showed strong tolerance to salinity stress. Overexpression of OsWNK9 also triggered the accumulation of abscisic acid (ABA) and restored indole-3-acetic acid (IAA) concentrations in roots, triggering stomatal closure in shoots and maintaining cell expansion of the root epidermal cells when challenged with salt treatment. The overexpression lines showed increased activity of antioxidant enzymes, which further mitigated ROS-mediated cellular damage under salinity stress. We also identified that OsWNK9 interacts with Receptor for Activated Kinase C1A (RACK1A), ABA-8'-hydroxylase, and (Vacuolar Type ATPase) V-Type ATPase. Taken together, our findings suggest that OsWNK9 expression is warranted under salinity stress and exerts its effects by interacting with its downstream targets and by increased accumulation of ABA and IAA, thereby regulating seed germination, stomatal activity, improved root growth, and ionic homeostasis, which all contribute to significantly higher yield produced per plant under long term salinity stress.

Agrobacterium-mediated transient transformation of Flaveria bidentis leaves: a novel method to examine the evolution of C4 photosynthesis

The genus Flaveria has been studied extensively as a model for the evolution of C4 photosynthesis. Thus far, molecular analyses in this genus have been limited due to a dearth of genomic information and the lack of a rapid and efficient transformation protocol. Since their development, Agrobacterium-mediated transient transformation protocols have been instrumental in understanding many biological processes in a range of plant species. However, this technique has not been applied to the genus Flaveria. Here, an efficient protocol for the Agrobacterium-mediated transient transformation of the leaves of the C4 species Flaveria bidentis is presented. This technique has the distinct advantages of rapid turnaround, the ability to co-transform with multiple constructs, and the capacity to assay coding and non-coding regions of Flaveria genomes in a homologous context. To illustrate the utility of this protocol, the quantitative transcriptional regulation of phosphoenolpyruvate carboxylase, the primary carboxylase of C4 plants, was investigated. A 24 bp region in the ppcA1 proximal promoter was found to elicit high levels of reporter gene expression. The Agrobacterium-mediated transient transformation of F. bidentis leaves will accelerate the understanding of the biology and evolution of C4 photosynthesis in the genus Flaveria as well as in other C4 lineages.

Production of the antimalarial drug precursor amorphadiene by microbial terpene synthase-like from the moss Sanionia uncinata

MAIN CONCLUSION

The microbial terpene synthase-like of the moss Sanionia uncinata displays the convergent evolution of a rare plant metabolite amorpha-4,11-diene synthesis. Despite increasing demand for the exploration of biological resources, the diversity of natural compounds synthesized by organisms inhabiting various climates remains largely unexplored. This study focuses on the moss Sanionia uncinata, known as a predominant species within the polar climates of the Antarctic Peninsula, to systematically explore its metabolic profile both in-field and in controlled environments. We here report a diverse array of moss-derived terpene volatiles, including the identification of amorpha-4,11-diene, a rare sesquiterpene compound that is a precursor for antimalarial drugs. Phylogenetic reconstruction and functional validation in planta and in vitro identified a moss terpene synthase, S. uncinata microbial terpene synthase-like 2 (SuMTPSL2), which is associated with amorpha-4,11-diene production. We demonstrate that expressing SuMTPSL2 in various heterologous systems is sufficient to produce amorpha-4,11-diene. These results highlight the metabolic diversity in Antarctica, but also provide insights into the convergent evolution leading to the synthesis of a rare plant metabolite.

The LpHsfA2-molecular module confers thermotolerance via fine tuning of its transcription in perennial ryegrass (Lolium perenne L.)

Temperature sensitivity and tolerance play a key role in plant survival and production. Perennial ryegrass (Lolium perenne L.), widely cultivated in cool-season for forage supply and turfgrass, is extremely susceptible to high temperatures, therefore serving as an excellent grass for dissecting the genomic and genetic basis of high-temperature adaptation. In this study, expression analysis revealed that LpHsfA2, an important gene associated with high-temperature tolerance in perennial ryegrass, is rapidly and substantially induced under heat stress. Additionally, heat-tolerant varieties consistently display elevated expression levels of LpHsfA2 compared with heat-sensitive ones. Comparative haplotype analysis of the LpHsfA2 promoter indicated an uneven distribution of two haplotypes (HsfA2Hap1 and HsfA2Hap2) across varieties with differing heat tolerance. Specifically, the HsfA2Hap1 allele is predominantly present in heat-tolerant varieties, while the HsfA2Hap2 allele exhibits the opposite pattern. Overexpression of LpHsfA2 confers enhanced thermotolerance, whereas silencing of LpHsfA2 compromises heat tolerance. Furthermore, LpHsfA2 orchestrates its protective effects by directly binding to the promoters of LpHSP18.2 and LpAPX1 to activate their expression, preventing the non-specific misfolding of intracellular protein and the accumulation of reactive oxygen species in cells. Additionally, LpHsfA4 and LpHsfA5 were shown to engage directly with the promoter of LpHsfA2, upregulating its expression as well as the expression of LpHSP18.2 and LpAPX1, thus contributing to enhanced heat tolerance. Markedly, LpHsfA2 possesses autoregulatory ability by directly binding to its own promoter to modulate the self-transcription. Based on these findings, we propose a model for modulating the thermotolerance of perennial ryegrass by precisely regulating the expression of LpHsfA2. Collectively, these findings provide a scientific basis for the development of thermotolerant perennial ryegrass cultivars.

The structure and interaction of polymers affects secondary cell wall banding patterns in Arabidopsis

Xylem tracheary elements (TEs) synthesize patterned secondary cell walls (SCWs) to reinforce against the negative pressure of water transport. VASCULAR-RELATED NAC-DOMAIN 7 (VND7) induces differentiation, accompanied by cellulose, xylan, and lignin deposition into banded domains. To investigate the effect of polymer biosynthesis mutations on SCW patterning, we developed a method to induce tracheary element transdifferentiation of isolated protoplasts, by transient transformation with VND7. Our data showed that proper xylan elongation is necessary for distinct cellulose bands, cellulose-xylan interactions are essential for coincident polymer patterns, and cellulose deposition is needed to override the intracellular organization that yields unique xylan patterns. These data indicate that a properly assembled cell wall network acts as a scaffold to direct polymer deposition into distinctly banded domains. We describe the transdifferentiation of protoplasts into TEs, providing an avenue to study patterned SCW biosynthesis in a tissue-free environment and in various mutant backgrounds.

The BnaBPs gene regulates flowering time and leaf angle in Brassica napus

The flowering time and plant architecture of Brassica napus were significantly associated with yield. In this study, we found that the BREVIPEDICELLUS/KNAT1(BP) gene regulated the flowering time and plant architecture of B. napus. However, the precise regulatory mechanism remains unclear. We cloned two homologous BP genes, BnaBPA03 and BnaBPC03, from B. napus Xiaoyun. The protein sequence analysis showed two proteins containing conserved domains KNOX I, KNOX II, ELK, and HOX of the KONX protein family. The CRISPR/Cas9 knockout lines exhibited early budding and flowering time, coupled with floral organ abscission earlier and a larger leaf angle. On the contrary, overexpression plants displayed a phenotype that was the inverse of these characteristics. Furthermore, we observed upregulation of gibberellin and ethylene biosynthesis genes, as well as floral integrator genes in knocked-out plants. The results revealed that BnaBPs play a role in flowering time, floral organ abscission, and leaf angle as well as germination processes mediated. Additionally, BnaBPs exerted an impact on the biosynthesis pathways of ethylene and GA.

Genome-Wide Identification of TLP Gene Family in Populus trichocarpa and Functional Characterization of PtTLP6, Preferentially Expressed in Phloem

Thaumatin-like proteins (TLPs) in plants are involved in diverse biotic and abiotic stresses, including antifungal activity, low temperature, drought, and high salinity. However, the roles of the TLP genes are rarely reported in early flowering. Here, the TLP gene family was identified in P. trichocarpa. The 49 PtTLP genes were classified into 10 clusters, and gene structures, conserved motifs, and expression patterns were analyzed in these PtTLP genes. Among 49 PtTLP genes, the PtTLP6 transcription level is preferentially high in stems, and GUS staining signals were mainly detected in the phloem tissues of the PtTLP6pro::GUS transgenic poplars. We generated transgenic Arabidopsis plants overexpressing the PtTLP6 gene, and its overexpression lines showed early flowering phenotypes. However, the expression levels of main flowering regulating genes were not significantly altered in these PtTLP6-overexpressing plants. Our data further showed that overexpression of the PtTLP6 gene led to a reactive oxygen species (ROS) burst in Arabidopsis, which might advance the development process of transgenic plants. In addition, subcellular localization of PtTLP6-fused green fluorescent protein (GFP) was in peroxisome, as suggested by tobacco leaf transient transformation. Overall, this work provides a comprehensive analysis of the TLP gene family in Populus and an insight into the role of TLPs in woody plants.

Safflower CtFLS1-Induced Drought Tolerance by Stimulating the Accumulation of Flavonols and Anthocyanins in Arabidopsis thaliana

Flavonol synthase gene (FLS) is a member of the 2-oxoglutarate-dependent dioxygenase (2-ODD) superfamily and plays an important role in plant flavonoids biosynthetic pathways. Safflower (Carthamus tinctorius L.), a key source of traditional Chinese medicine, is widely cultivated in China. Although the flavonoid biosynthetic pathway has been studied in several model species, it still remains to be explored in safflower. In this study, we aimed to elucidate the role of CtFLS1 gene in flavonoid biosynthesis and drought stress responses. The bioinformatics analysis on the CtFLS1 gene showed that it contains two FLS-specific motifs (PxxxIRxxxEQP and SxxTxLVP), suggesting its independent evolution. Further, the expression level of CtFLS1 in safflower showed a positive correlation with the accumulation level of total flavonoid content in four different flowering stages. In addition, CtFLS1-overexpression (OE) Arabidopsis plants significantly induced the expression levels of key genes involved in flavonol pathway. On the contrary, the expression of anthocyanin pathway-related genes and MYB transcription factors showed down-regulation. Furthermore, CtFLS1-OE plants promoted seed germination, as well as resistance to osmotic pressure and drought, and reduced sensitivity to ABA compared to mutant and wild-type plants. Moreover, CtFLS1 and CtANS1 were both subcellularly located at the cell membrane and nucleus; the yeast two-hybrid and bimolecular fluorescence complementation (BiFC) assay showed that they interacted with each other at the cell membrane. Altogether, these findings suggest the positive role of CtFLS1 in alleviating drought stress by stimulating flavonols and anthocyanin accumulation in safflower.

Comparative analysis of R2R3-MYB transcription factors in the flower of Iris laevigata identifies a novel gene regulating tobacco cold tolerance

Breeding for flower cold resistance is a priority for flower breeding research in northern China. The identification of cold resistance genes will not only provide genetic resources for cold resistance breeding, but also form a basis for the study of plant cold resistance mechanisms. Based on the flower transcriptome of Iris laevigata, 20 R2R3-MYBs were identified and comprehensive analysis, including conservative domain, phylogenetic analyses and functional distribution, were performed for R2R3-MYBs. Expression patterns of the abiotic stress genes under cold stress were detected, the upregulated gene was genetically transformed into tobacco, and the related physiological indicators of the transgenic tobacco were measured. A novel cold resistance gene, IlMYB306, was obtained. qRT-PCR indicated that IlMYB306 was dramatically induced by cold stress and was significantly upregulated in roots. The free proline content, MDA, SOD and POD activity of the transgenic tobacco improved after cold stress, and the chlorophyll content decreased slowly. In addition, overexpression of IlMYB306 improved cold resistance of the seeds. SEM results showed leaves of transgenic tobacco had obvious folds, more grooves and bulges on the lower leaf surface. Overall, we report a novel cold resistance R2R3-MYB gene, IlMYB306, in the flower of I. laevigata, which could improve tobacco cold stress tolerance by thickening the waxy layer, increasing antioxidant activity and the content of proline.

Mesophyll conductance is unaffected by expression of Arabidopsis PIP1 aquaporins in the plasmalemma of Nicotiana

In plants with C3 photosynthesis, increasing the diffusion conductance for CO2 from the substomatal cavity to chloroplast stroma (mesophyll conductance) can improve the efficiencies of both CO2 assimilation and photosynthetic water use. In the diffusion pathway from substomatal cavity to chloroplast stroma, the plasmalemma and chloroplast envelope membranes impose a considerable barrier to CO2 diffusion, limiting photosynthetic efficiency. In an attempt to improve membrane permeability to CO2, and increase photosynthesis in tobacco, we generated transgenic lines in Nicotiana tabacum L. cv Petite Havana carrying either the Arabidopsis PIP1;2 (AtPIP1;2) or PIP1;4 (AtPIP1;4) gene driven by the constitutive dual 2x35S CMV promoter. From a collection of independent T0 transgenics, two T2 lines from each gene were characterized, with western blots confirming increased total aquaporin protein abundance in the AtPIP1;2 tobacco lines. Transient expression of AtPIP1;2-mGFP6 and AtPIP1;4-mGFP6 fusions in Nicotiana benthamiana identified that both AtPIP1;2 and AtPIP1;4 localize to the plasmalemma. Despite achieving ectopic production and correct localization, gas exchange measurements combined with carbon isotope discrimination measurements detected no increase in mesophyll conductance or CO2 assimilation rate in the tobacco lines expressing AtPIP. We discuss the complexities associated with trying to enhance gm through modified aquaporin activity.

Rapid Investigation of Functional Roles of Genes in Regulation of Leaf Senescence Using Arabidopsis Protoplasts

Leaf senescence is the final stage of leaf development preceding death, which involves a significant cellular metabolic transition from anabolism to catabolism. Several processes during leaf senescence require coordinated regulation by senescence regulatory genes. In this study, we developed a rapid and systematic cellular approach to dissect the functional roles of genes in senescence regulation through their transient expression in Arabidopsis protoplasts. We established and validated this system by monitoring the differential expression of a luciferase-based reporter that was driven by promoters of SEN4 and SAG12, early and late senescence-responsive genes, depending on effectors of known positive and negative senescence regulators. Overexpression of positive senescence regulators, including ORE1, RPK1, and RAV1, increased the expression of both SEN4- and SAG12-LUC while ORE7, a negative senescence regulator decreased their expression. Consistently with overexpression, knockdown of target genes using amiRNAs resulted in opposite SAG12-LUC expression patterns. The timing and patterns of reporter responses induced by senescence regulators provided molecular evidence for their distinct kinetic involvement in leaf senescence regulation. Remarkably, ORE1 and RPK1 are involved in cell death responses, with more prominent and earlier involvement of ORE1 than RPK1. Consistent with the results in protoplasts, further time series of reactive oxygen species (ROS) and cell death assays using different tobacco transient systems reveal that ORE1 causes acute cell death and RPK1 mediates superoxide-dependent intermediate cell death signaling during leaf senescence. Overall, our results indicated that the luciferase-based reporter system in protoplasts is a reliable experimental system that can be effectively used to examine the regulatory roles of Arabidopsis senescence-associated genes.

The Arabidopsis small G-protein AtRAN1 is a positive regulator in chitin-induced stomatal closure and disease resistance

Chitin, a fungal microbial-associated molecular pattern, triggers various defence responses in several plant systems. Although it induces stomatal closure, the molecular mechanisms of its interactions with guard cell signalling pathways are unclear. Based on screening of public microarray data obtained from the ATH1 Affymetrix and Arabidopsis eFP browser, we isolated a cDNA encoding a Ras-related nuclear protein 1 AtRAN1. AtRAN1 expression was enriched in guard cells in a manner consistent with involvement in the control of the stomatal movement. AtRAN1 mutation impaired chitin-induced stomatal closure and accumulation of reactive oxygen species and nitric oxide in guard cells. In addition, Atran1 mutant plants exhibited compromised chitin-enhanced plant resistance to both bacterial and fungal pathogens due to changes in defence-related genes. Furthermore, Atran1 mutant plants were hypersensitive to drought stress compared to Col-0 plants, and had lower levels of stress-responsive genes. These data demonstrate a previously uncharacterized signalling role for AtRAN1, mediating chitin-induced signalling.

Transient Gene Expression is an Effective Experimental Tool for the Research into the Fine Mechanisms of Plant Gene Function: Advantages, Limitations, and Solutions

A large data array on plant gene expression accumulated thanks to comparative omic studies directs the efforts of researchers to the specific or fine effects of the target gene functions and, as a consequence, elaboration of relatively simple and concurrently effective approaches allowing for the insight into the physiological role of gene products. Numerous studies have convincingly demonstrated the efficacy of transient expression strategy for characterization of the plant gene functions. The review goals are (i) to consider the advantages and limitations of different plant systems and methods of transient expression used to find out the role of gene products; (ii) to summarize the current data on the use of the transient expression approaches for the insight into fine mechanisms underlying the gene function; and (iii) to outline the accomplishments in efficient transient expression of plant genes. In general, the review discusses the main and critical steps in each of the methods of transient gene expression in plants; areas of their application; main results obtained using plant objects; their contribution to our knowledge about the fine mechanisms of the plant gene functions underlying plant growth and development; and clarification of the mechanisms regulating complex metabolic pathways.

Engineering Tropane Alkaloid Production Based on Metabolic Characterization of Ornithine Decarboxylase in Atropa belladonna

Ornithine decarboxylase (ODC) plays an important role in various biological processes; however, its role in plant secondary metabolism, especially in the biosynthesis of tropane alkaloids (TAs) such as pharmaceutical hyoscyamine, anisodamine, and scopolamine, remains largely unknown. In this study, we characterized the physiological and metabolic functions of the ODC gene of Atropa belladonna (AbODC) and determined its role in TA production using metabolic engineering approaches. Feeding assays with enzyme inhibitors indicated that ODC, rather than arginine decarboxylase (ADC), plays a major role in TA biosynthesis. Tissue-specific AbODC expression analysis and β-glucuronidase (GUS) staining assays showed that AbODC was highly expressed in secondary roots, especially in the cylinder tissue. Enzymatic assays indicated that AbODC was able to convert ornithine to putrescine, with the highest activity at pH 8.0 and 30 °C. Additionally, AbODC showed higher catalytic efficiency than other plant ODCs, as evident from the K_m, V_max, and K_cat values of AbODC using ornithine as the substrate. In A. belladonna root cultures, suppression of AbODC greatly reduced the production of putrescine, N-methylputrescine, and TAs, whereas overexpression of AbODC significantly increased the biosynthesis of putrescine, N-methylputrescine, hyoscyamine, and anisodamine. Moreover, transgenic A. belladonna plants overexpressing AbODC showed a significantly higher production of hyoscyamine and anisodamine compared with control plants. These findings indicate that AbODC plays a key role in TA biosynthesis and therefore is a valuable candidate for increasing TA production in A. belladonna.

Combining a Simple Method for DNA/RNA/Protein Co-Purification and Arabidopsis Protoplast Assay to Facilitate Viroid Research

Plant–viroid interactions represent a valuable model for delineating structure–function relationships of noncoding RNAs. For various functional studies, it is desirable to minimize sample variations by using DNA, RNA, and proteins co-purified from the same samples. Currently, most of the co-purification protocols rely on TRI Reagent (Trizol as a common representative) and require protein precipitation and dissolving steps, which render difficulties in experimental handling and high-throughput analyses. Here, we established a simple and robust method to minimize the precipitation steps and yield ready-to-use RNA and protein in solutions. This method can be applied to samples in small quantities, such as protoplasts. Given the ease and the robustness of this new method, it will have broad applications in virology and other disciplines in molecular biology.

I see the light! Fluorescent proteins suitable for cell wall/apoplast targeting in Nicotiana benthamiana leaves

Correct subcellular targeting is crucial for protein function. Protein location can be visualized in vivo by fusion to a fluorescent protein (FP). Nevertheless, despite intense engineering efforts, most FPs are dim or completely quenched at low pH (<6). This is particularly problematic for the study of proteins targeted to acidic compartments such as vacuoles (pH ~ 3-6) or plant cell walls (pH ~ 3.5-8.3). Plant cell walls play important roles (e.g. structural/protective role, control of growth/morphogenesis), are diverse in structure and function, and are highly dynamic (e.g. during cell growth, in response to biotic/abiotic stresses). To study and engineer plant cell walls, it is therefore critical to identify robust tools which can be used to locate proteins expressed in the apoplast. Here we used a transient expression assay in Nicotiana benthamiana leaves to test a range of FPs in vivo, and determined which ones retained strong fluorescence in the acidic environment of the apoplast. We selected 10 fluorescent proteins with a range of in vitro properties; two historical FPs and eight FPs with in vitro properties suggesting lower pH sensitivity or improved brightness, some of which had never been tested in plants prior to our study. We targeted each FP to the cytosol or the apoplast and compared the fluorescence in both compartments, before testing the in vivo pH sensitivity of FPs across a pH 8-4 gradient. Our results suggest that mTurquoise2, mNeonGreen, and mCherry are suited to tracking proteins in the apoplast under dynamic pH conditions. These fluorescent proteins may also be useful in other acidic compartments such as vacuoles.