A remorin gene SiREM6, the target gene of SiARDP, from foxtail millet (Setaria italica) promotes high salt tolerance in transgenic Arabidopsis

Major transcription factor families at the nexus of regulating abiotic stress response in millets: a comprehensive review

Millets stand out as a sustainable crop with the potential to address the issues of food insecurity and malnutrition. These small-seeded, drought-resistant cereals have adapted to survive a broad spectrum of abiotic stresses. Researchers are keen on unravelling the regulatory mechanisms that empower millets to withstand environmental adversities. The aim is to leverage these identified genetic determinants from millets for enhancing the stress tolerance of major cereal crops through genetic engineering or breeding. This review sheds light on transcription factors (TFs) that govern diverse abiotic stress responses and play role in conferring tolerance to various abiotic stresses in millets. Specifically, the molecular functions and expression patterns of investigated TFs from various families, including bHLH, bZIP, DREB, HSF, MYB, NAC, NF-Y and WRKY, are comprehensively discussed. It also explores the potential of TFs in developing stress-tolerant crops, presenting a comprehensive discussion on diverse strategies for their integration.

Identification and characterization of the Remorin gene family in Saccharum and the involvement of ScREM1.5e-1/-2 in SCMV infection on sugarcane

Introduction

Remorins (REMs) are plant-specific membrane-associated proteins that play important roles in plant-pathogen interactions and environmental adaptations. Group I REMs are extensively involved in virus infection. However, little is known about the REM gene family in sugarcane (Saccharum spp. hyrid), the most important sugar and energy crop around world.

Methods

Comparative genomics were employed to analyze the REM gene family in Saccharum spontaneum. Transcriptomics or RT-qPCR were used to analyze their expression files in different development stages or tissues under different treatments. Yeast two hybrid, bimolecular fluorescence complementation and co-immunoprecipitation assays were applied to investigate the protein interaction.

Results

In this study, 65 REMs were identified from Saccharum spontaneum genome and classified into six groups based on phylogenetic tree analysis. These REMs contain multiple cis-elements associated with growth, development, hormone and stress response. Expression profiling revealed that among different SsREMs with variable expression levels in different developmental stages or different tissues. A pair of alleles, ScREM1.5e-1/-2, were isolated from the sugarcane cultivar ROC22. ScREM1.5e-1/-2 were highly expressed in leaves, with the former expressed at significantly higher levels than the latter. Their expression was induced by treatment with H2O2, ABA, ethylene, brassinosteroid, SA or MeJA, and varied upon Sugarcane mosaic virus (SCMV) infection. ScREM1.5e-1 was localized to the plasma membrane (PM), while ScREM1.5e-2 was localized to the cytoplasm or nucleus. ScREM1.5e-1/-2 can self-interact and interact with each other, and interact with VPgs from SCMV, Sorghum mosaic virus, or Sugarcane streak mosaic virus. The interactions with VPgs relocated ScREM1.5e-1 from the PM to the cytoplasm.

Discussion

These results reveal the origin, distribution and evolution of the REM gene family in sugarcane and may shed light on engineering sugarcane resistance against sugarcane mosaic pathogens.

Protein Disorder in Plant Stress Adaptation: From Late Embryogenesis Abundant to Other Intrinsically Disordered Proteins

Global climate change has caused severe abiotic and biotic stresses, affecting plant growth and food security. The mechanical understanding of plant stress responses is critical for achieving sustainable agriculture. Intrinsically disordered proteins (IDPs) are a group of proteins without unique three-dimensional structures. The environmental sensitivity and structural flexibility of IDPs contribute to the growth and developmental plasticity for sessile plants to deal with environmental challenges. This article discusses the roles of various disordered proteins in plant stress tolerance and resistance, describes the current mechanistic insights into unstructured proteins such as the disorder-to-order transition for adopting secondary structures to interact with specific partners (i.e., cellular membranes, membrane proteins, metal ions, and DNA), and elucidates the roles of liquid-liquid phase separation driven by protein disorder in stress responses. By comparing IDP studies in animal systems, this article provides conceptual principles of plant protein disorder in stress adaptation, reveals the current research gaps, and advises on the future research direction. The highlighting of relevant unanswered questions in plant protein disorder research aims to encourage more studies on these emerging topics to understand the mechanisms of action behind their stress resistance phenotypes.

Molecular characterization and expression analysis of the remorin genes in tomato (Solanum lycopersicum L.)

Remorin (REMs) are plant-specific and plasma membrane-associated proteins that play an essential role in the growth and development of plants and adaptations to adverse environments. To our knowledge, a genome-scale investigation of the REM genes in tomato has never been systematically studied. In this study, a total of 17 SlREM genes were identified in the tomato genome using bioinformatics methods. Our results demonstrated that the 17 members of SlREM were classified into 6 groups based on phylogenetic analysis and unevenly distributed on the eight chromosomes of tomato. There were 15 REM homologous gene pairs between tomato and Arabidopsis. The SlREM gene structures and motif compositions were similar. Promoter sequence analysis showed that the SlREM gene promoters contained some tissue-specific, hormones and stress-related cis-regulatory elements. Expression analysis based on qRT-PCR (Real-time quantitative PCR) analysis showed that SlREM family genes were were differentially expressed in different tissues, and they responded to ABA, MeJA, SA, low-temperature, drought and NaCl treatments. These results potentially provide relevant information for further research on the biological functions of SlREM family genes.

CaREM1.4 interacts with CaRIN4 to regulate Ralstonia solanacearum tolerance by triggering cell death in pepper

Remorins, plant-specific proteins, have a significant role in conferring on plants the ability to adapt to adverse environments. However, the precise function of remorins in resistance to biological stress remains largely unknown. Eighteen CaREM genes were identified in pepper genome sequences based on the C-terminal conserved domain that is specific to remorin proteins in this research. Phylogenetic relations, chromosomal localization, motif, gene structures, and promoter regions of these remorins were analyzed and a remorin gene, CaREM1.4, was cloned for further study. The transcription of CaREM1.4 in pepper was induced by infection with Ralstonia solanacearum. Knocking down CaREM1.4 in pepper using virus-induced gene silencing (VIGS) technologies reduced the resistance of pepper plants to R. solanacearum and downregulated the expression of immunity-associated genes. Conversely, transient overexpression of CaREM1.4 in pepper and Nicotiana benthamiana plants triggered hypersensitive response-mediated cell death and upregulated expression of defense-related genes. In addition, CaRIN4-12, which interacted with CaREM1.4 at the plasma membrane and cell nucleus, was knocked down with VIGS, decreasing the susceptibility of Capsicum annuum to R. solanacearum. Furthermore, CaREM1.4 reduced ROS production by interacting with CaRIN4-12 upon co-injection in pepper. Taken together, our findings suggest that CaREM1.4 may function as a positive regulator of the hypersensitive response, and it interacts with CaRIN4-12, which negatively regulates plant immune responses of pepper to R. solanacearum. Our study provides new evidence for comprehending the molecular regulatory network of plant cell death.

Genetic enhancement of climate-resilient traits in small millets: A review

Agriculture is facing the challenge of feeding the ever-growing population that is projected to reach ten billion by 2050. While improving crop yield and productivity can address this challenge, the increasing effects of global warming and climate change seriously threaten agricultural productivity. Thus, genomics and genome modification technologies are crucial to improving climate-resilient traits to enable sustained yield and productivity; however, significant research focuses on staple crops such as rice, wheat, and maize. Crops that are naturally climate-resilient and nutritionally superior to staple cereals, such as small millets, remain neglected and underutilized by mainstream research. The ability of small millets to grow in marginal regions having limited irrigation and poor soil fertility makes these crops a better choice for cultivation in arid and semi-arid areas. Hence, mainstreaming small millets for cultivation and using omics technologies to dissect the climate-resilient traits to identify the molecular determinants underlying these traits are imperative for addressing food and nutritional security. In this context, the review discusses the genomics and genome modification approaches for dissecting key traits in small millets and their application for improving these traits in cultivated germplasm. The review also discusses biofortification for nutritional security and machine-learning approaches for trait improvement in small millets. Altogether, the review provides a roadmap for the effective use of next-generation approaches for trait improvement in small millets. This will lead to the development of improved varieties for addressing multiple insecurities prevailing in the present climate change scenario.

Membrane Proteins in Plant Salinity Stress Perception, Sensing, and Response

Plants have several mechanisms to endure salinity stress. The degree of salt tolerance varies significantly among different terrestrial crops. Proteins at the plant's cell wall and membrane mediate different physiological roles owing to their critical positioning between two distinct environments. A specific membrane protein is responsible for a single type of activity, such as a specific group of ion transport or a similar group of small molecule binding to exert multiple cellular effects. During salinity stress in plants, membrane protein functions: ion homeostasis, signal transduction, redox homeostasis, and solute transport are essential for stress perception, signaling, and recovery. Therefore, comprehensive knowledge about plant membrane proteins is essential to modulate crop salinity tolerance. This review gives a detailed overview of the membrane proteins involved in plant salinity stress highlighting the recent findings. Also, it discusses the role of solute transporters, accessory polypeptides, and proteins in salinity tolerance. Finally, some aspects of membrane proteins are discussed with potential applications to developing salt tolerance in crops.

Stabilization of membrane topologies by proteinaceous remorin scaffolds

In plants, the topological organization of membranes has mainly been attributed to the cell wall and the cytoskeleton. Additionally, few proteins, such as plant-specific remorins have been shown to function as protein and lipid organizers. Root nodule symbiosis requires continuous membrane re-arrangements, with bacteria being finally released from infection threads into membrane-confined symbiosomes. We found that mutations in the symbiosis-specific SYMREM1 gene result in highly disorganized perimicrobial membranes. AlphaFold modelling and biochemical analyses reveal that SYMREM1 oligomerizes into antiparallel dimers and may form a higher-order membrane scaffolding structure. This was experimentally confirmed when expressing this and other remorins in wall-less protoplasts is sufficient where they significantly alter and stabilize de novo membrane topologies ranging from membrane blebs to long membrane tubes with a central actin filament. Reciprocally, mechanically induced membrane indentations were equally stabilized by SYMREM1. Taken together we describe a plant-specific mechanism that allows the stabilization of large-scale membrane conformations independent of the cell wall.

Membrane Proteomic Profiling of Soybean Leaf and Root Tissues Uncovers Salt-Stress-Responsive Membrane Proteins

Cultivated soybean (Glycine max (L.)), the world's most important legume crop, has high-to-moderate salt sensitivity. Being the frontier for sensing and controlling solute transport, membrane proteins could be involved in cell signaling, osmoregulation, and stress-sensing mechanisms, but their roles in abiotic stresses are still largely unknown. By analyzing salt-induced membrane proteomic changes in the roots and leaves of salt-sensitive soybean cultivar (C08) seedlings germinated under NaCl, we detected 972 membrane proteins, with those present in both leaves and roots annotated as receptor kinases, calcium-sensing proteins, abscisic acid receptors, cation and anion channel proteins, proton pumps, amide and peptide transporters, and vesicle transport-related proteins etc. Endocytosis, linoleic acid metabolism, and fatty acid biosynthesis pathway-related proteins were enriched in roots whereas phagosome, spliceosome and soluble NSF attachment protein receptor (SNARE) interaction-related proteins were enriched in leaves. Using label-free quantitation, 129 differentially expressed membrane proteins were found in both tissues upon NaCl treatment. Additionally, the 140 NaCl-induced proteins identified in roots and 57 in leaves are vesicle-, mitochondrial-, and chloroplast-associated membrane proteins and those with functions related to ion transport, protein transport, ATP hydrolysis, protein folding, and receptor kinases, etc. Our proteomic results were verified against corresponding gene expression patterns from published C08 RNA-seq data, demonstrating the importance of solute transport and sensing in salt stress responses.

Combined QTL mapping and RNA-Seq pro-filing reveal candidate genes related to low-temperature tolerance in maize

Maize (Zea mays L.) is the most important food crop in the world, with significant acreage and production across the globe. However, it is affected by low temperatures throughout its growth process, especially during germination. Therefore, it is important to identify more QTLs or genes associated with germination under low-temperature conditions. For the QTL analysis of traits related to low-temperature germination, we used a high-res genetic map of 213 lines of the intermated B73 × Mo17 (IBM) Syn10 doubled haploid (DH) population, which had 6618 bin markers. We detected 28 QTLs of eight phenotypic characteristics associated with low-temperature germination, while they explained the phenotypic contribution rate of 5.4 ~ 13.34%. Additionally, 14 overlapping QTLs produced six QTL clusters on every chromosome, except for 8 and 10. RNA-Seq found six genes related to low-temperature tolerance in these QTLs, while qRT-PCR analysis demonstrated that the expression trends of the Zm00001d045568 gene in the LT_BvsLT_M group and the CK_BvsCK_M group were highly significantly different at all four-time points (P < 0.01), and encoded the RING zinc finger protein. It was located on qRTL9-2 and qRSVI9-1 and is related to the total length and simple vitality index. These results provided potential candidate genes for further gene cloning and improving the low-temperature tolerance of maize.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01297-6.

Improvement of millets in the post-genomic era

Millets are food and nutrient security crops in the semi-arid tropics of developing countries. Crop improvement using modern tools is one of the priority areas of research in millets. The whole-genome sequence (WGS) of millets provides new insight into understanding and studying the genes, genome organization and genomic-assisted improvement of millets. The WGS of millets helps to carry out genome-wide comparison and co-linearity studies among millets and other cereal crops. This approach might lead to the identification of genes underlying biotic and abiotic stress tolerance in millets. The available genome sequence of millets can be used for SNP identification, allele discovery, association and linkage mapping, identification of valuable candidate genes, and marker-assisted breeding (MAB) programs. Next generation sequencing (NGS) technology provides opportunities for genome-assisted breeding (GAB) through genomic selection (GS) and genome-wide association studies (GAWS) for crop improvement. Clustered, regularly interspaced, short palindromic repeats (CRISPR)-CRISPR-associated protein 9 (Cas9) genome editing (GE) system provides new opportunities for millet improvement. In this review, we discuss the details on the WGS available for millets and highlight the importance of utilizing such resources in the post-genomic era for millet improvement. We also draw inroads on the utilization of various approaches such as GS, GWAS, functional genomics, gene validation and GE for millet improvement. This review might be helpful for understanding the developments in the post-genomic era of millet improvement.

Transcriptome analysis of Kentucky bluegrass subject to drought and ethephon treatment

Kentucky bluegrass (Poa pratensis L.) is an excellent cool-season turfgrass utilized widely in Northern China. However, turf quality of Kentucky bluegrass declines significantly due to drought. Ethephon seeds-soaking treatment has been proved to effectively improve the drought tolerance of Kentucky bluegrass seedlings. In order to investigate the effect of ethephon leaf-spraying method on drought tolerance of Kentucky bluegrass and understand the underlying mechanism, Kentucky bluegrass plants sprayed with and without ethephon are subjected to either drought or well watered treatments. The relative water content and malondialdehyde conent were measured. Meanwhile, samples were sequenced through Illumina. Results showed that ethephon could improve the drought tolerance of Kentucky bluegrass by elevating relative water content and decreasing malondialdehyde content under drought. Transcriptome analysis showed that 58.43% transcripts (254,331 out of 435,250) were detected as unigenes. A total of 9.69% (24,643 out of 254,331) unigenes were identified as differentially expressed genes in one or more of the pairwise comparisons. Differentially expressed genes due to drought stress with or without ethephon pre-treatment showed that ethephon application affected genes associated with plant hormone, signal transduction pathway and plant defense, protein degradation and stabilization, transportation and osmosis, antioxidant system and the glyoxalase pathway, cell wall and cuticular wax, fatty acid unsaturation and photosynthesis. This study provides a theoretical basis for revealing the mechanism for how ethephon regulates drought response and improves drought tolerance of Kentucky bluegrass.

Tomato leaves under stress: a comparison of stress response to mild abiotic stress between a cultivated and a wild tomato species

Tomato is one of the most produced crop plants on earth and growing in the fields and greenhouses all over the world. Breeding with known traits of wild species can enhance stress tolerance of cultivated crops. In this study, we investigated responses of the transcriptome as well as primary and secondary metabolites in leaves of a cultivated and a wild tomato to several abiotic stresses such as nitrogen deficiency, chilling or warmer temperatures, elevated light intensities and combinations thereof. The wild species responded different to varied temperature conditions compared to the cultivated tomato. Nitrogen deficiency caused the strongest responses and induced in particular the secondary metabolism in both species but to much higher extent in the cultivated tomato. Our study supports the potential of a targeted induction of valuable secondary metabolites in green residues of horticultural production, that will otherwise only be composted after fruit harvest. In particular, the cultivated tomato showed a strong induction in the group of mono caffeoylquinic acids in response to nitrogen deficiency. In addition, the observed differences in stress responses between cultivated and wild tomato can lead to new breeding targets for better stress tolerance.

Melatonin Enhances Seed Germination and Seedling Growth of Medicago sativa Under Salinity via a Putative Melatonin Receptor MsPMTR1

Alfalfa (Medicago sativa L.) is an important forage crop, and salt stress is a major limiting factor in its yield. Melatonin (MT) is a multi-regulatory molecule in plants. We showed that basal MT content was positively correlated with the salt tolerance degree of different alfalfa varieties. MT and its precursor 5-HT fully recovered seed germination while partially ameliorated seedling growth of salt-stressed alfalfa. The 5-HT showed some divergent effects from MT with regards to growth amelioration under salinity. Salt stress caused stunted plant growth in soil culture, while MT ameliorated it by elevating plant height, fresh weight, branching number, and chlorophyll content. Silencing of a putative MT receptor, MsPMTR1, which was shown to be membrane-localized, abolished the ameliorative effects of MT on salt-stressed alfalfa seedling growth, while overexpression of MsPMTR1 improved plant growth under salt stress. The RNA sequencing analysis showed that nine pathway genes were specifically induced by MT treatment compared with salt stress. These MT-responsive differentially expressed genes include basal metabolic pathway genes, such as "ribosome, elongation factor," "sugar and lipid metabolism," and "photosynthesis" and stress-related genes encoding "membrane integrity" related proteins, heat shock protein, peroxidase/oxidoreductase, and protease. Several abiotic stress response-related genes, such as DRE, ARF, HD-ZF, MYB, and REM were repressed by NaCl treatment while induced by MT treatment. In summary, we demonstrated the importance of MsPMTR1 in MT-mediated salt tolerance in alfalfa, and we also analyzed the regulatory mechanism of MT during alfalfa seed germination under salt stress.

Genetics and breeding for climate change in Orphan crops

Climate change is rapidly changing how we live, what we eat and produce, the crops we breed and the target traits. Previously underutilized orphan crops that are climate resilient are receiving much attention from the crops research community, as they are often the only crops left in the field after periods of extreme weather conditions. There are several orphan crops with incredible resilience to biotic and abiotic stresses. Some are nutritious, while others provide good sources of biofuel, medicine and other industrial raw materials. Despite these benefits, orphan crops are still lacking in important genetic and genomic resources that could be used to fast track their improvement and make their production profitable. Progress has been made in generating draft genomes of at least 28 orphan crops over the last decade, thanks to the reducing cost of sequencing. The implementation of a structured breeding program that takes advantage of additional modern crop improvement tools such as genomic selection, speed breeding, genome editing, high throughput phenotyping and breeding digitization would make rapid improvement of these orphan crops possible, but would require coordinated research investment. Other production challenges such as lack of adequate germplasm conservation, poor/non-existent seed systems and agricultural extension services, as well as poor marketing channels will also need to be improved if orphan crops were to be profitable. We review the importance of breeding orphan crops under the increasing effects of climate change, highlight existing gaps that need to be addressed and share some lessons to be learned from major crops.

Connecting the dots: from nanodomains to physiological functions of REMORINs

REMORINs (REMs) are a plant-specific protein family, proposed regulators of membrane-associated molecular assemblies and well-established markers of plasma membrane nanodomains. REMs play a diverse set of functions in plant interactions with pathogens and symbionts, responses to abiotic stresses, hormone signaling and cell-to-cell communication. In this review, we highlight the established and more putative roles of REMs throughout the literature. We discuss the physiological functions of REMs, the mechanisms underlying their nanodomain-organization and their putative role as regulators of nanodomain-associated molecular assemblies. Furthermore, we discuss how REM phosphorylation may regulate their functional versatility. Overall, through data-mining and comparative analysis of the literature, we suggest how to further study the molecular mechanisms underpinning the functions of REMs.

Populus euphratica remorin 6.5 activates plasma membrane H+-ATPases to mediate salt tolerance

Remorins (REMs) play an important role in the ability of plants to adapt to adverse environments. PeREM6.5, a protein of the REM family in Populus euphratica (salt-resistant poplar), was induced by NaCl stress in callus, roots and leaves. We cloned the full-length PeREM6.5 from P. euphratica and transformed it into Escherichia coli and Arabidopsis thaliana. PeREM6.5 recombinant protein significantly increased the H+-ATPase hydrolytic activity and H+ transport activity in P. euphratica plasma membrane (PM) vesicles. Yeast two-hybrid assay showed that P. euphratica REM6.5 interacted with RPM1-interacting protein 4 (PeRIN4). Notably, the PeREM6.5-induced increase in PM H+-ATPase activity was enhanced by PeRIN4 recombinant protein. Overexpression of PeREM6.5 in Arabidopsis significantly improved salt tolerance in transgenic plants in terms of survival rate, root growth, electrolyte leakage and malondialdehyde content. Arabidopsis plants overexpressing PeREM6.5 retained high PM H+-ATPase activity in both in vivo and in vitro assays. PeREM6.5-transgenic plants had reduced accumulation of Na+ due to the Na+ extrusion promoted by the H+-ATPases. Moreover, the H+ pumps caused hyperpolarization of the PM, which reduced the K+ loss mediated by the depolarization-activated channels in the PM of salinized roots. Therefore, we conclude that PeREM6.5 regulated H+-ATPase activity in the PM, thus enhancing the plant capacity to maintain ionic homeostasis under salinity.

Organization and dynamics of functional plant membrane microdomains

Plasma membranes are heterogeneous and laterally compartmentalized into distinct microdomains. These membrane microdomains consist of special lipids and proteins and are thought to act as signaling platforms. In plants, membrane microdomains have been detected by super-resolution microscopy, and there is evidence that they play roles in several biological processes. Here, we review current knowledge about the lipid and protein components of membrane microdomains. Furthermore, we summarize the dynamics of membrane microdomains in response to different stimuli. We also explore the biological functions associated with membrane microdomains as signal integration hubs. Finally, we outline challenges and questions for further studies.

Comparative proteomics combined with analyses of transgenic plants reveal ZmREM1.3 mediates maize resistance to southern corn rust

Southern corn rust (SCR), which is a destructive disease caused by Puccinia polysora Underw. (P. polysora), commonly occurs in warm-temperate and tropical regions. To identify candidate proteins related to SCR resistance and characterize the molecular mechanisms underlying the maize-P. polysora interaction, a comparative proteomic analysis of susceptible and resistant maize lines was performed. Statistical analyses revealed 1489 differentially abundant proteins in the resistant line, as well as 1035 differentially abundant proteins in the susceptible line. After the P. polysora infection, the abundance of one remorin protein (ZmREM1.3) increased in the resistant genotype, but decreased in the susceptible genotype. Plant-specific remorins are important for responses to microbial infections as well as plant signalling processes. In this study, transgenic maize plants overexpressing ZmREM1.3 exhibited enhanced resistance to the biotrophic P. polysora. In contrast, homozygous ZmREM1.3 UniformMu mutant plants were significantly more susceptible to P. polysora than wild-type plants. Additionally, the ZmREM1.3-overexpressing plants accumulated more salicylic acid (SA) and jasmonic acid (JA). Moreover, the expression levels of defence-related genes were higher in ZmREM1.3-overexpressing maize plants than in non-transgenic control plants in response to the P. polysora infection. Overall, our results provide evidence that ZmREM1.3 positively regulates maize defences against P. polysora likely via SA/JA-mediated defence signalling pathways. This study represents the first large-scale proteomic analysis of the molecular mechanisms underlying the maize-P. polysora interaction. This is also the first report confirming the remorin protein family affects plant resistance to SCR.

Genome-Wide Identification and Characterization of the Wheat Remorin (TaREM) Family during Cold Acclimation

Remorins (REMs) are plant-specific proteins that play an essential role in plant-microbe interactions. However, their roles in vernalization and abiotic stress responses remain speculative. Most remorins have a variable proline-rich -half and a more conserved -half that is predicted to form coils. A search of the wheat ( L.) database revealed the existence of 20 different genes, which we classified into six groups on the basis of whether they shared a common phylogenetic and structural origin. Analysis of the physical genomic distributions demonstrated that genes are dispersed in the wheat genome and have one to seven introns. Promoter analysis of genes revealed the presence of putative -elements related to diverse functions like development, hormonal regulation, and biotic and abiotic stress responsiveness. Expression levels of genes were measured in plants grown under field and controlled conditions and in response to hormone treatment. Our analyses revealed that 12 members of the REM family are regulated during cold acclimation in wheat in four different tissues (roots, crowns, stems, and leaves), with the highest expression in roots. Differential gene expression was found between wheat cultivars with contrasting degrees of cold tolerance, suggesting the implication of genes in cold response and tolerance. Additionally, eight genes were induced in response to abscisic acid and methyl jasmonate treatment. This genome-wide analysis of genes provides valuable resources for functional analysis aimed at understanding their role in stress adaptation.

Rhizosheath formation and involvement in foxtail millet (Setaria italica) root growth under drought stress

The rhizosheath, a layer of soil particles that adheres firmly to the root surface by a combination of root hairs and mucilage, may improve tolerance to drought stress. Setaria italica (L.) P. Beauv. (foxtail millet), a member of the Poaceae family, is an important food and fodder crop in arid regions and forms a larger rhizosheath under drought conditions. Rhizosheath formation under drought conditions has been studied, but the regulation of root hair growth and rhizosheath size in response to soil moisture remains unclear. To address this question, in this study we monitored root hair growth and rhizosheath development in response to a gradual decline in soil moisture. Here, we determined that a soil moisture level of 10%-14% (w/w) stimulated greater rhizosheath production compared to other soil moisture levels. Root hair density and length also increased at this soil moisture level, which was validated by measurement of the expression of root hair-related genes. These findings contribute to our understanding of rhizosheath formation in response to soil water stress.

REM1.3's phospho-status defines its plasma membrane nanodomain organization and activity in restricting PVX cell-to-cell movement

Plants respond to pathogens through dynamic regulation of plasma membrane-bound signaling pathways. To date, how the plant plasma membrane is involved in responses to viruses is mostly unknown. Here, we show that plant cells sense the Potato virus X (PVX) COAT PROTEIN and TRIPLE GENE BLOCK 1 proteins and subsequently trigger the activation of a membrane-bound calcium-dependent kinase. We show that the Arabidopsis thaliana CALCIUM-DEPENDENT PROTEIN KINASE 3-interacts with group 1 REMORINs in vivo, phosphorylates the intrinsically disordered N-terminal domain of the Group 1 REMORIN REM1.3, and restricts PVX cell-to-cell movement. REM1.3's phospho-status defines its plasma membrane nanodomain organization and is crucial for REM1.3-dependent restriction of PVX cell-to-cell movement by regulation of callose deposition at plasmodesmata. This study unveils plasma membrane nanodomain-associated molecular events underlying the plant immune response to viruses.

Viruses propagate in plants through membranous channels, called plasmodesmata, linking each cell to its neighboring cell. In this work, we challenge the role of the plasma membrane in the regulation of virus propagation. By studying the dynamics and the activation of a plant-specific protein called REMORIN, we found that the way this protein is organized inside the membrane is crucial to fulfill its function in the immunity of plants against viruses.

The mode of action of remorin1 in regulating fruit ripening at transcriptional and post-transcriptional levels

Remorins are plant-specific and plasma membrane-associated proteins that display a variety of functions in plant growth, development, biotic and abiotic stresses, and signal transduction. However, little information is available for understanding their role in fruit ripening. Here, remorin 1 (SlREM1) is cloned from tomato and its localization is examined by co-localization analysis and immunoblotting. Functions of SlREM1 in fruit ripening are characterized based on gene expression, co-immunoprecipitation coupled with mass spectroscopy and split luciferase complementation imaging assays in SlREM1 overexpression and RNA interference (RNAi) lines. The results indicate that SlREM1 is localized at the plasma membrane. Overexpression of SlREM1 in tomato stimulates fruit ripening with an increase in ethylene production and lycopene accumulation as compared to the wild-type. Consistently, these genes involved in ethylene and lycopene biosynthesis and ripening regulators also are upregulated in SlREM1 overexpression lines. SlREM1 can interact with ethylene biosynthesis proteins SAM1, ACO1 and ACS2 and is degraded by ubiquitin-mediated proteolysis. Our findings reveal that SlREM1 serves as a positive regulator of fruit ripening and provide novel cues for understanding of the molecular regulation network of fruit ripening.

Symbiotic root infections in Medicago truncatula require remorin-mediated receptor stabilization in membrane nanodomains

Plant cell infection is tightly controlled by cell surface receptor-like kinases (RLKs). Like other RLKs, the Medicago truncatula entry receptor LYK3 laterally segregates into membrane nanodomains in a stimulus-dependent manner. Although nanodomain localization arises as a generic feature of plant membrane proteins, the molecular mechanisms underlying such dynamic transitions and their functional relevance have remained poorly understood. Here we demonstrate that actin and the flotillin protein FLOT4 form the primary and indispensable core of a specific nanodomain. Infection-dependent induction of the remorin protein and secondary molecular scaffold SYMREM1 results in subsequent recruitment of ligand-activated LYK3 and its stabilization within these membrane subcompartments. Reciprocally, the majority of this LYK3 receptor pool is destabilized at the plasma membrane and undergoes rapid endocytosis in symrem1 mutants on rhizobial inoculation, resulting in premature abortion of host cell infections. These data reveal that receptor recruitment into nanodomains is indispensable for their function during host cell infection.

Optimization of Phenotyping Assays for the Model Monocot Setaria viridis

Setaria viridis (green foxtail) is an important model plant for the study of C4 photosynthesis in panicoid grasses, and is fast emerging as a system of choice for the study of plant development, domestication, abiotic stress responses and evolution. Basic research findings in Setaria are expected to advance research not only in this species and its close relative S. italica (foxtail millet), but also in other panicoid grasses, many of which are important food or bioenergy crops. Here we report on the standardization of multiple growth and development assays for S. viridis under controlled conditions, and in response to several phytohormones and abiotic stresses. We optimized these assays at three different stages of the plant's life: seed germination and post-germination growth using agar plate-based assays, early seedling growth and development using germination pouch-based assays, and adult plant growth and development under environmentally controlled growth chambers and greenhouses. These assays will be useful for the community to perform large scale phenotyping analyses, mutant screens, comparative physiological analysis, and functional characterization of novel genes of Setaria or other related agricultural crops. Precise description of various growth conditions, effective treatment conditions and description of the resultant phenotypes will help expand the use of S. viridis as an effective model system.

OsREM4.1 Interacts with OsSERK1 to Coordinate the Interlinking between Abscisic Acid and Brassinosteroid Signaling in Rice

Crosstalk among phytohormones is crucial for balancing plant growth and adjustment to various environments. Abscisic acid (ABA) and brassinosteroids (BRs) exhibit antagonistic interactions during many plant development processes, but little is known about the molecular mechanism mediating those interactions. Here, we identified a rice (Oryza sativa) remorin gene, OsREM4.1, whose expression is upregulated by ABA through the transcriptional activator OsbZIP23. OsREM4.1, in return, negatively regulates BR signaling output. We discovered that OsREM4.1 interacts with OsSERK1 to inhibit its interaction with rice BR receptor OsBRI1. Moreover, OsBRI1 could phosphorylate OsREM4.1 to reduce the binding affinity of OsREM4.1 to OsSERK1. These results demonstrate that OsREM4.1 is transcriptionally regulated by ABA and functions as an OsBRI1 substrate and OsSERK1-interacting protein to inhibit the formation and subsequent activation of the OsBRI1-OsSERK1 receptor complex. Our findings provide insight into the mechanism by which the antagonistic interactions between ABA and BRs are coordinated in rice.

Constitutive expression of DaCBF7, an Antarctic vascular plant Deschampsia antarctica CBF homolog, resulted in improved cold tolerance in transgenic rice plants

Deschampsia antarctica is an Antarctic hairgrass that grows on the west coast of the Antarctic peninsula. In this report, we have identified and characterized a transcription factor, D. antarctica C-repeat binding factor 7 (DaCBF7), that is a member of the monocot group V CBF homologs. The protein contains a single AP2 domain, a putative nuclear localization signal, and the typical CBF signature. DaCBF7, like other monocot group V homologs, contains a distinct polypeptide stretch composed of 43 amino acids in front of the AP2 motif. DaCBF7 was predominantly localized to nuclei and interacted with the C-repeat/dehydration responsive element (CRT/DRE) core sequence (ACCGAC) in vitro. DaCBF7 was induced by abiotic stresses, including drought, cold, and salinity. To investigate its possible cellular role in cold tolerance, a transgenic rice system was employed. DaCBF7-overexpressing transgenic rice plants (Ubi:DaCBF7) exhibited markedly increased tolerance to cold stress compared to wild-type plants without growth defects; however, overexpression of DaCBF7 exerted little effect on tolerance to drought or salt stress. Transcriptome analysis of a Ubi:DaCBF7 transgenic line revealed 13 genes that were up-regulated in DaCBF7-overexpressing plants compared to wild-type plants in the absence of cold stress and in short- or long-term cold stress. Five of these genes, dehydrin, remorin, Os03g63870, Os11g34790, and Os10g22630, contained putative CRT/DRE or low-temperature responsive elements in their promoter regions. These results suggest that overexpression of DaCBF7 directly and indirectly induces diverse genes in transgenic rice plants and confers enhanced tolerance to cold stress.

Molecular principles of membrane microdomain targeting in plants

Plasma membranes (PMs) are heterogeneous lipid bilayers comprising diverse subdomains. These sites can be labeled by various proteins in vivo and may serve as hotspots for signal transduction. They are found at apical, basal, and lateral membranes of polarized cells, at cell equatorial planes, or almost isotropically distributed throughout the PM. Recent advances in imaging technologies and understanding of mechanisms that allow proteins to target specific sites in PMs have provided insights into the dynamics and complexity of their specific segregation. Here we present a comprehensive overview of the different types of membrane microdomain and describe the molecular modes that determine site-directed targeting of membrane-resident proteins at the PM.

Grain setting defect1 (GSD1) function in rice depends on S-acylation and interacts with actin 1 (OsACT1) at its C-terminal

Grain setting defect1 (GSD1), a plant-specific remorin protein specifically localized at the plasma membrane (PM) and plasmodesmata of phloem companion cells, affects grain setting in rice through regulating the transport of photoassimilates. Here, we show new evidence demonstrating that GSD1 is localized at the cytoplasmic face of the PM and a stretch of 45 amino acid residues at its C-terminal is required for its localization. Association with the PM is mediated by S-acylation of cysteine residues Cys-524 and Cys-527, in a sequence of 45 amino acid residues essential for GSD1 function in rice. Furthermore, the coiled-coil domain in GSD1 is necessary for sufficient interaction with OsACT1. Together, these results reveal that GSD1 attaches to the PM through S-acylation and interacts with OsACT1 through its coiled-coil domain structure to regulate plasmodesmata conductance for photoassimilate transport in rice.