MdGRF11, an apple 14-3-3 protein, acts as a positive regulator of drought and salt tolerance

Sensing, Adapting and Thriving: How Fruit Crops Combat Abiotic Stresses

Production of high-yield and high-quality fruits is always the long-term objective of fruit crop cultivation, which, however, is challenged by various abiotic stresses such as drought, extreme temperatures and high salinity, and the adverse impacts of abiotic stresses on fruit crops are exacerbated by climate change in recent years. To cope with these environmental stressors, fruit crops have evolved adaptative strategies involving physiological changes and molecular regulation. In this review, we summarise the relevent changes in photosynthesis, osmotic and reactive oxygen species (ROS) equilibrium, metabolism and protein homeostasis in response to abiotic stresses. Moreover, perception of environmental stimuli as well as recent progress of underlying regulatory mechanisms is also discussed. Based on our current knowledge, possible strategies for stress resilience improvement in fruit crops are accordingly proposed. In addition, we also discuss the challenges in identification of key nodes in plant responses to multiple stresses and development of stress-resilient fruit crops, and addressing these issues in the future would advance our understanding of how fruit crops combat abiotic stresses and facilitate the breeding of superior fruit crops that can adapt to and thrive in the changing environments.

MdHMGB15-MdXERICO-MdNRP module mediates salt tolerance of apple by regulating the expression of salt stress-related genes

INTRODUCTION

Soil salinity is an important limiting factor for plant growth. As a RING-type E3 ubiquitin ligase, MdXERICO is highly responsive to salt stress and can enhance the salt tolerance of plants. However, the molecular mechanism for the response of MdXERICO to salt stress remains unclear.

OBJECTIVES

This study aims to dissect the molecular mechanisms for MdXERICO to regulate plant response to salt stress.

METHODS

Transcriptome data were compared to obtain the salt stress-induced gene MdXERICO. Transgenic apple seedlings, apple calli, Arabidopsis, and tomato material were obtained using Agrobacterium-mediated transformation assays. Semiendogenous co-immunoprecipitation analysis, yeast two-hybrid, pull-down and dual-luciferase reporter system were used to detect the protein-protein interactions. Electrophoretic mobility shift assay, yeast one-hybrids, dual luciferase and Gus staining assay were employed to verify the protein-DNA interactions.

RESULTS

The results revealed that MdXERICO interacted with MdNRP and improved salt tolerance of apple by ubiquitinating and degrading MdNRP via the 26S proteasome pathway. Moreover, the HMG box-containing transcription factor MdHMGB15 interacted with the MdXERICO promoter, thereby activating its expression and enhancing the salt tolerance of apple.

CONCLUSION

This study explores the apple's tolerance to salt stress through the MdHMGB15-MdXERICO-MdNRP module, and provides potential targets for engineering salt-tolerant varieties.

The MdCo gene encodes a putative 2OG-Fe (II) oxygenase that positively regulates salt tolerance in transgenic tomato and apple

Salinity stress is a significant environmental factor that impacts the growth, development, quality, and yield of crops. The 2OG-Fe (II) oxygenase family of enzyme proteins plays crucial roles in plant growth and stress responses. Previously, we identified and characterized MdCo, which encodes a putative 2OG-Fe (II) oxygenase, a key gene for controlling the columnar growth habit of apples. In this study, we explored the role of MdCo in salt stress tolerance. Expression analysis suggested that MdCo exhibits high expression in roots and is significantly induced by NaCl stress. Ectopic expression of MdCo exhibited enhanced salt stress tolerance in transgenic tomatoes, and these plants were characterized by better growth performance, and higher chlorophyll content, but lower electrolyte leakage and malondialdehyde (MDA), and less hydrogen peroxide (H2O2) and superoxide radicals (O2-) under salt stress. Overexpression of MdCo can effectively scavenge reactive oxygen species (ROS) by enhancing the activities of antioxidant enzymes and up-regulating the expression of stress-associated genes under salt stress, thereby enhancing salt tolerance in apple calli. Collectively, these findings provide new insights into the function of MdCo in salt stress tolerance as well as future potential application for apple breeding aimed at improving salt stress tolerance.

Evaluation of Salt Resistance of Six Apple Rootstocks

Apples (Malus domestica Borkh) are important fruits in China; however, salt stress is severe in northern regions, and the key to plant resistance to salt stress lies in the rootstock. Therefore, it is necessary to explore rootstocks with strong salt resistance for the development of the apple industry. This study used tissue culture seedlings of six apple rootstocks, namely, '71-3-150', '54-118', 'M9T337', 'GM256', 'ML176', and 'ML2', as experimental materials. The seedlings were treated with a medium containing 150 mM NaCl, and the physiological indicators and related gene expression responses of several rootstocks were studied after salt stress. The results showed that salt stress affects the growth of both the aboveground and underground parts of plants. Through physiological indicators and the related gene expression responses of rootstocks, it was observed that salt stress significantly increased Na+ contents in different rootstocks. Simultaneously, the activity of various antioxidant enzymes and the expression levels of related genes also increased. In summary, by analyzing the parameters of various physiological indicators, it can be concluded that among the studied rootstocks, the '71-3-150' and '54-118' rootstocks have the strongest resistance to salt stress, while the 'M9T337' and 'GM256' rootstocks exhibit moderate resistance, and the 'ML176' and 'ML2' rootstocks have the weakest resistance.

Functional Characterization of the 14-3-3 Gene Family in Alfalfa and the Role of MsGRF2 in Drought Response Mechanisms

Drought stress affects crop growth and development, significantly reducing crop yield and quality. Alfalfa (Medicago sativa L.), the most widely cultivated forage crop, is particularly susceptible to drought. The general regulatory factor (GRF) protein 14-3-3, a highly conserved family in plants, specifically recognizes and binds to phosphoserine residues in target proteins, regulating both plant development and responses to environmental stressors. In this study, 66 alfalfa 14-3-3 proteins were identified, and the full-length MsGRF2 gene was cloned and functionally analyzed. The expression of MsGRF2 was highest in alfalfa inflorescences and lowest in roots. Transgenic tobacco overexpressing MsGRF2 exhibited increased tolerance to low temperature and drought stress, evidenced by physiological indicators including low levels of active oxygen species and increased activity of antioxidant enzymes and osmoregulatory substances. Under drought stress conditions, compared to wild-type plants, MsGRF2-overexpressing tobacco plants exhibited significantly increased expression of drought stress-related genes ERD10B and TIP, while the expression of BRI1, Cu/Zn-SOD, ERF2, and KC1 was significantly reduced. Together, these results provide new insights into the roles of the 14-3-3 protein MsGRF2 in plant drought response mechanisms.

Utilizing machine learning and bioinformatics analysis to identify drought-responsive genes affecting yield in foxtail millet

Drought stress is a major constraint on crop development, potentially causing huge yield losses and threatening global food security. Improving Crop's stress tolerance is usually associated with a yield penalty. One way to balance yield and stress tolerance is modification specific gene by emerging precision genome editing technology. However, our knowledge of yield-related drought-tolerant genes is still limited. Foxtail millet (Setaria italica) has a remarkable tolerance to drought and is considered to be a model C4 crop that is easy to engineer. Here, we have identified 46 drought-responsive candidate genes by performing a machine learning-based transcriptome study on two drought-tolerant and two drought-sensitive foxtail millet cultivars. A total of 12 important drought-responsive genes were screened out by principal component analysis and confirmed experimentally by qPCR. Significantly, by investigating the haplotype of these genes based on 1844 germplasm resources, we found two genes (Seita.5G251300 and Seita.8G036300) exhibiting drought-tolerant haplotypes that possess an apparent advantage in 1000 grain weight and main panicle grain weight without penalty in grain weight per plant. These results demonstrate the potential of Seita.5G251300 and Seita.8G036300 for breeding drought-tolerant high-yielding foxtail millet. It provides important insights for the breeding of drought-tolerant high-yielding crop cultivars through genetic manipulation technology.

Cloning and functional identification of apple LATERAL ORGAN BOUNDARY DOMAIN 3 (LBD3) transcription factor in the regulation of drought and salt stress

MAIN CONCLUSION

Overexpression of MdLBD3 in Arabidopsis reduced sensitivity to salt and drought stresses and was instrumental in promoting early flowering. Salt and drought stresses have serious effects on plant growth. LATERAL ORGAN BOUNDARY DOMAIN (LBD) proteins are a plant-specific transcription factors (TFs) family and play important roles in plants in resisting to abiotic stress. However, about the function of LBDs in apple and other woody plants is little known. In this study, protein sequences of the LBD family TFs in apples were identified which contained conserved LOB domains. The qRT-PCR analysis showed that the MdLBD3 gene was widely expressed in various tissues and organs. The subcellular localization assay showed that the MdLBD3 protein was localized in the nucleus. Ectopic expression of MdLBD3 in Arabidopsis positively regulated its salt and drought resistance, and promoted early flowering. Collectively, these results showed that MdLBD3 improved the abiotic stress resistance, plant growth and development. Overall, this study provided a new gene for breeding that can increase the abiotic stress tolerance in apple.

The 14-3-3 protein GRF8 modulates salt stress tolerance in apple via the WRKY18-SOS pathway

Salinity is a severe abiotic stress that limits plant survival, growth, and development. 14-3-3 proteins are phosphopeptide-binding proteins that are involved in numerous signaling pathways, such as metabolism, development, and stress responses. However, their roles in salt tolerance are unclear in woody plants. Here, we characterized an apple (Malus domestica) 14-3-3 gene, GENERAL REGULATORY FACTOR 8 (MdGRF8), the product of which promotes salinity tolerance. MdGRF8 overexpression improved salt tolerance in apple plants, whereas MdGRF8-RNA interference (RNAi) weakened it. Yeast 2-hybrid, bimolecular fluorescence complementation, pull-down, and coimmunoprecipitation assays revealed that MdGRF8 interacts with the transcription factor MdWRKY18. As with MdGRF8, overexpressing MdWRKY18 enhanced salt tolerance in apple plants, whereas silencing MdWRKY18 had the opposite effect. We also determined that MdWRKY18 binds to the promoters of the salt-related genes SALT OVERLY SENSITIVE 2 (MdSOS2) and MdSOS3. Moreover, we showed that the 14-3-3 protein MdGRF8 binds to the phosphorylated form of MdWRKY18, enhancing its stability and transcriptional activation activity. Our findings reveal a regulatory mechanism by the MdGRF8-MdWRKY18 module for promoting the salinity stress response in apple.

Molecular evolution and interaction of 14-3-3 proteins with H+-ATPases in plant abiotic stresses

Environmental stresses severely affect plant growth and crop productivity. Regulated by 14-3-3 proteins (14-3-3s), H+-ATPases (AHAs) are important proton pumps that can induce diverse secondary transport via channels and co-transporters for the abiotic stress response of plants. Many studies demonstrated the roles of 14-3-3s and AHAs in coordinating the processes of plant growth, phytohormone signaling, and stress responses. However, the molecular evolution of 14-3-3s and AHAs has not been summarized in parallel with evolutionary insights across multiple plant species. Here, we comprehensively review the roles of 14-3-3s and AHAs in cell signaling to enhance plant responses to diverse environmental stresses. We analyzed the molecular evolution of key proteins and functional domains that are associated with 14-3-3s and AHAs in plant growth and hormone signaling. The results revealed evolution, duplication, contraction, and expansion of 14-3-3s and AHAs in green plants. We also discussed the stress-specific expression of those 14-3-3and AHA genes in a eudicotyledon (Arabidopsis thaliana), a monocotyledon (Hordeum vulgare), and a moss (Physcomitrium patens) under abiotic stresses. We propose that 14-3-3s and AHAs respond to abiotic stresses through many important targets and signaling components of phytohormones, which could be promising to improve plant tolerance to single or multiple environmental stresses.

The 14-3-3 Protein BdGF14a Increases the Transcriptional Regulation Activity of BdbZIP62 to Confer Drought and Salt Resistance in Tobacco

BdGF14a, a 14-3-3 gene from Brachypodium distachyon, induced by salt, H2O2, and abscisic acid (ABA), improved tolerance to drought and salt in tobacco, with a higher survival rate and longer roots under these stresses. Additionally, physiological index analyses showed that the heterologous expression of BdGF14a induced higher expression levels of antioxidant enzymes and their activities, leading to lighter DAB and NBT staining, denoting decreased H2O2 content. Additionally, the lower MDA content and ion leakage indicated enhanced cell membrane stability. Moreover, exogenous ABA resulted in shorter roots and a lower stomatal aperture in BdGF14a transgenic plants. BdGF14a interacted with NtABF2 and regulated the expression of stress-related genes. However, adding an ABA biosynthesis inhibitor suppressed most of these changes. Furthermore, similar salt and drought resistance phenotypes and physiological indicators were characterized in tobacco plants expressing BdbZIP62, an ABRE/ABF that interacts with BdGF14a. And Y1H and LUC assays showed that BdGF14a could enhance the transcription regulation activity of NtABF2 and BdbZIP62, targeting NtNECD1 by binding to the ABRE cis-element. Thus, BdGF14a confers resistance to drought and salinity through interaction with BdbZIP62 and enhances its transcriptional regulation activity via an ABA-mediated signaling pathway. Therefore, this work offers novel target genes for breeding salt- and drought-tolerant plants.

MdGRF11-MdARF19-2 module acts as a positive regulator of drought resistance in apple rootstock

14-3-3 proteins play an important role in the response of plants to drought resistance. In this study, 14-3-3 protein MdGRF11 was cloned from Malus xiaojinensis, and its positive regulation of drought resistance was verified using Orin calli and M. xiaojinensis plants. The transcription factor MdARF19-2 was further screened for interaction with this protein in vitro and in vivo. We also conducted experiments using Orin calli and found that the overexpression of MdARF19-2 decreased the level of reactive oxygen species (ROS) and increased the activity of enzymes that scavenge ROS in plant materials. This indicates that MdARF19-2 is a positive regulator in the drought resistance of plants. The drought tolerance was further improved by the overexpression of both MdGRF11 and MdARF19-2 in the calli. In addition, we examined several genes related to ROS scavenging with auxin response factor binding elements in their promoters and found that their level of expression was regulated by the MdGRF11-MdARF19-2 module. In conclusion, the enhancement of plant drought resistance by MdGRF11 could be owing to its accumulation at the protein level in response to drought, which then combined with MdARF19-2, affecting the expression of MdARF19-2 downstream genes. Thus, it scavenges ROS, which ultimately improves the resistance of plant to drought stress.

Using association mapping and local interval haplotype association analysis to improve the cotton drought stress response

Drought stress has a serious impact on the growth and development of cotton. To explore the relevant molecular mechanism of the drought stress response in cotton, gene mapping based on the QTL interval mapped by simplified genome BSA-seq of the drought-resistance-related RIL population was performed. A QTL region spanning 2.02 Mb on chromosome D07 was selected, and 201 resource materials were genotyped using 9 KASP markers in the interval. After local interval haplotype association analysis, the overlap of the 110 kb peak region confirmed the reliability of this region, and at the same time, the role of GhGF14-30, the only gene in the overlapping region, was modeled in the response of cotton to drought stress. qRTPCR analysis of the materials and population parents proved that this gene plays a role in the drought stress response in cotton. Virus-induced gene silencing proved the importance of this gene in drought-sensitive materials, and drought-resistance-related marker genes also proved that the GhGF14-30 gene may play an important role in the ABA and SOS signaling pathways. This study provides a basis for mining drought stress response functional genes in cotton and lays the foundation for the molecular mechanism of the GhGF14-30 gene in response to drought stress in cotton.

Evolution of the 14-3-3 gene family in monocotyledons and dicotyledons and validation of MdGRF13 function in transgenic Arabidopsis thaliana

KEY MESSAGE

The 14-3-3 family is more highly conserved among monocotyledons, and overexpression of MdGRF13 improved drought and salt tolerance in transgenic Arabidopsis thaliana. The 14-3-3 are highly conserved regulatory proteins found in eukaryotes and play an essential role in plant growth, development and stress response. However, the 14-3-3 gene family evolution in monocotyledons and dicotyledons and the biological functions of the MdGRF13 under abiotic stress remain unknown. In our study, 195 members of the 14-3-3 family were identified from 12 species and divided into ε group and the Non-ε group. Synteny analysis within the 14-3-3 family indicated that segmental duplication events contributed to the expansion of the family. Selective pressure analysis indicated that purifying selection was a vital force in the 14-3-3 genes evolution, and monocotyledons had a lower million years ago (Mya) mean values than dicotyledons. Meanwhile, the codon adaptation index (CAI) and frequency of optical codons (FOP) are higher and the effective number of codons (Nc) is lower in monocotyledons 14-3-3 genes compared to dicotyledons. Moreover, the yeast two-hybrid (Y2H) demonstrated that MdGRF13 interacts with MdRD22, MdLHP1a and MdMORF1. Significantly, the malondialdehyde (MDA) content and relative conductivity were decreased, while the superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities were increased in transgenic Arabidopsis compared to the wild type (WT) under drought and salt stress. These results suggest that overexpression of MdGRF13 significantly improved the tolerance to drought and salt stress in transgenic Arabidopsis. Thus, our results provide a theoretical basis for exploring the evolution and function of the 14-3-3 gene family in monocotyledons and dicotyledons.

Ectopic expression of MmSERT, a mouse serotonin transporter gene, regulates salt tolerance and ABA sensitivity in apple and Arabidopsis

5-hydroxytryptamine (5-HT) is ubiquitously present in animals and plants, playing a vital regulatory role. SERT, a conserved serotonin reuptake transporter in animals, regulates intracellular and extracellular concentrations of 5-HT. Few studies have reported 5-HT transporters in plants. Hence, we cloned MmSERT, a serotonin reuptake transporter, from Mus musculus. Ectopic expression of MmSERT into apple calli, apple roots and Arabidopsis. Because 5-HT plays a momentous role in plant stress tolerance, we used MmSERT transgenic materials for stress treatment. We found that MmSERT transgenic materials, including apple calli, apple roots and Arabidopsis, exhibited a stronger salt tolerance phenotype. The reactive oxygen species (ROS) produced were significantly lower in MmSERT transgenic materials compared with controls under salt stress. Meanwhile, MmSERT induced the expression of SOS1, SOS3, NHX1, LEA5 and LTP1 in response to salt stress. 5-HT is the precursor of melatonin, which regulates plant growth under adversity and effectively scavenges ROS. Detection of MmSERT transgenic apple calli and Arabidopsis revealed higher melatonin levels than controls. Besides, MmSERT decreased the sensitivity of apple calli and Arabidopsis to abscisic acid (ABA). In summary, these results demonstrated that MmSERT plays a vital role in plant stress resistances, which perhaps serves as a reference for the application of transgenic technology to improve crops in the future.

A 14-3-3 protein positively regulates rice salt tolerance by stabilizing phospholipase C1

The phosphatidylinositol-specific phospholipase Cs (PI-PLCs) catalyze the hydrolysis of phosphatidylinositols, which play crucial roles in signaling transduction during plant development and stress response. However, the regulation of PI-PLC is still poorly understood. A previous study showed that a rice PI-PLC, OsPLC1, was essential to rice salt tolerance. Here, we identified a 14-3-3 protein, OsGF14b, as an interaction partner of OsPLC1. Similar to OsPLC1, OsGF14b also positively regulates rice salt tolerance, and their interaction can be promoted by NaCl stress. OsGF14b also positively regulated the hydrolysis activity of OsPLC1, and is essential to NaCl-induced activation of rice PI-PLCs. We further discovered that OsPLC1 was degraded via ubiquitin-proteasome pathway, and OsGF14b could inhibit the ubiquitination of OsPLC1 to protect OsPLC1 from degradation. Under salt stress, the OsPLC1 protein level in osgf14b was lower than the corresponding value of WT, whereas overexpression of OsGF14b results in a significant increase of OsPLC1 stability. Taken together, we propose that OsGF14b can interact with OsPLC1 and promote its activity and stability, thereby improving rice salt tolerance. This study provides novel insights into the important roles of 14-3-3 proteins in regulating protein stability and function in response to salt stress.

Genome-wide identification and characterization of tomato 14-3-3 (SlTFT) genes and functional analysis of SlTFT6 under heat stress

The plant 14-3-3 proteins are essential for many biological processes and responses to abiotic stress. We performed genome-wide identification and analysis of the 14-3-3 family genes in tomato. To explore the properties of the thirteen Sl14-3-3 found in the tomato genome, their chromosomal location, phylogenetic, and syntenic relationships were analyzed. The Sl14-3-3 promoters were found to have a number of growth-, hormone-, and stress-responsive cis-regulatory elements. Moreover, the qRT-PCR assay revealed that Sl14-3-3 genes are responsive to heat and osmotic stress. Subcellular localization experiments evidenced that the SlTFT3/6/10 proteins occur in the nucleus and cytoplasm Additional analysis on Sl14-3-3 putative interactor proteins revealed a number of prospective clients that potentially participate in stress reactions and developmental processes. Furthermore, overexpression of an Sl14-3-3 family gene, SlTFT6, improved tomato plants thermotolerance. Taken together, the study provides basic information on tomato 14-3-3 family genes in plant growth and abiotic stress response (high temperature stress), which can be helpful to further study the underlying molecular mechanisms.

Ectopic expression of MmCYP1A1, a mouse cytochrome P450 gene, positively regulates stress tolerance in apple calli and Arabidopsis

Ectopic expression of MmCYP1A1 gene from Mus musculus in apple calli and Arabidopsis increased the levels of melatonin and 6-hydroxymelatonin, and improved their stress resistance. Melatonin occurs widely in organisms, playing a key regulatory role. CYP1A1 is a cytochrome P450 monooxygenase, involved in the melatonin metabolism, and is responsible for the synthesis of 6-hydroxymelatonin from melatonin. Melatonin and 6-hydroxymelatonin have strong antioxidant activities in animals. Here, we cloned MmCYP1A1 from Mus musculus and found that ectopic expression of MmCYP1A1 improved the levels of melatonin and 6-hydroxymelatonin in transgenic apple calli and Arabidopsis. Subsequently, we observed that MmCYP1A1 increased the tolerance of transgenic apple calli and Arabidopsis to osmotic stress simulated by polyethylene glycol 6000 (PEG 6000), as well as resistance of transgenic Arabidopsis to drought stress. Further, the number of lateral roots of MmCYP1A1 transgenic Arabidopsis were enhanced significantly after PEG 6000 treatment. The expression of MmCYP1A1 remarkably reduced malondialdehyde (MDA) content, electrolyte leakage, accumulation of H₂O₂ and O₂^- during stress treatment. Moreover, MmCYP1A1 enhanced stress tolerance in apple calli and Arabidopsis by increasing the expression levels of resistance genes. MmCYP1A1 also promoted stomatal closure in transgenic Arabidopsis to reduce leaf water loss during drought. Our results indicate that MmCYP1A1 plays a key role in plant stress tolerance, which may provide a reference for future plant stress tolerance studies.

Genome-wide analysis of the 6B-INTERACTING PROTEIN1 gene family with functional characterization of MdSIP1-2 in Malus domestica

Trihelix transcription factors consist of five subfamilies, including GT-1, GT-2, SH4, GTγ, and SIP1, which play important roles in the responses to biotic and abiotic stresses, however, seldom is known about the role of the SIP1 genes in apples. In this study, 12 MdSIP1 genes were first identified in apples by genome-wide analysis, and contained conserved MYB/SANT-like domains. Expression patterns analyses showed that the MdSIP1 genes had different tissue expression patterns, and different transcription levels in response to abiotic stresses, indicating that MdSIP1s may play multiple roles under various abiotic stresses. Among them, the MdSIP1-2 gene was cloned and ectopic transformed into Arabidopsis, and its biology function was identified. The subcellular localization showed that MdSIP1-2 protein was specifically localized in the nucleus, and that overexpression of MdSIP1-2 promoted the development of lateral roots, increased abscisic acid (ABA) sensitivity, and improved salt and drought tolerance. These findings suggested that MdSIP1-2 plays an important role in root development, ABA synthesis, and salt and drought stress tolerance. In conclusion, these results lay a solid foundation for determining the role of MdSIP1 in the growth and development and abiotic stress tolerance of apples.

Molecular Evolution of Plant 14-3-3 Proteins and Function of Hv14-3-3A in Stomatal Regulation and Drought Tolerance

Drought significantly affects stomatal regulation, leading to the reduced growth and productivity of plants. Plant 14-3-3 proteins were reported to participate in drought response by regulating the activities of a wide array of target proteins. However, the molecular evolution, expression pattern and physiological functions of 14-3-3s under drought stress remain unclear. In this study, a comparative genomic analysis and the tissue-specific expression of 14-3-3s revealed the highly conserved and early evolution of 14-3-3s in green plants and duplication and expansion of the 14-3-3s family members in angiosperms. Using barley (Hordeum vulgare) for the functional characterization of 14-3-3 proteins, the transcripts of five members out of six Hv14-3-3s were highly induced by drought in the drought-tolerant line, XZ141. Suppression of the expression of Hv14-3-3A through barley stripe mosaic virus-virus induced gene silencing resulted in significantly increased drought sensitivity and stomatal density as well as significantly reduced net CO2 assimilation (A) and stomatal conductance (gs) in barley. Moreover, we showed the functional interactions between Hv14-3-3s and key proteins in drought and stomatal responses in plants-such as Open Stomata 1 (HvOST1), Slow Anion Channel 1 (HvSLAC1), three Heat Shock Proteins (HvHSP90-1/2/5) and Dehydration-Responsive Element-Binding 3 (HvDREB3). Taken together, we propose that 14-3-3s are highly evolutionarily conserved proteins and that Hv14-3-3s represent a group of the core regulatory components for the rapid stomatal response to drought in barley. This study will provide important evolutionary and molecular evidence for future applications of 14-3-3 proteins in breeding drought-tolerant crops in a changing global climate.

Functional characterization of MdERF113 in apple

The AP2/ERF family is an important class of transcription factors involved in plant growth and various biological processes. One of the AP2/ERF transcription factors, RAP2.6L, participates in various stresses responses. However, the function of RAP2.6L is largely unknown in apples (Malus domestica). In this study, an apple gene homologous to Arabidopsis AtRAP2.6L, MdERF113, was analyzed by bioinformatic characterization, gene expression analysis and subcellular localization assessment. MdERF113 was highly expressed in the sarcocarp and was responsive to hormonal signals and abiotic stresses. MdERF113-overexpression apple calli were less sensitive to low temperature, drought, salinity, and abscisic acid than wild-type. Subcellular localization revealed that MdERF113 was a nuclear-localized transcription factor, and yeast experiments confirmed that MdERF113 has no autonomous activation activity. Overall, this study indicated that MdERF113 plays a role in regulating plant growth under abiotic conditions.

The apple 14-3-3 gene MdGRF6 negatively regulates salt tolerance

The 14-3-3 (GRF, general regulatory factor) regulatory proteins are highly conserved and are widely distributed throughout the eukaryotes. They are involved in the growth and development of organisms via target protein interactions. Although many plant 14-3-3 proteins were identified in response to stresses, little is known about their involvement in salt tolerance in apples. In our study, nineteen apple 14-3-3 proteins were cloned and identified. The transcript levels of Md14-3-3 genes were either up or down-regulated in response to salinity treatments. Specifically, the transcript level of MdGRF6 (a member of the Md14-3-3 genes family) decreased due to salt stress treatment. The phenotypes of transgenic tobacco lines and wild-type (WT) did not affect plant growth under normal conditions. However, the germination rate and salt tolerance of transgenic tobacco was lower compared to the WT. Transgenic tobacco demonstrated decreased salt tolerance. The transgenic apple calli overexpressing MdGRF6 exhibited greater sensitivity to salt stress compared to the WT plants, whereas the MdGRF6-RNAi transgenic apple calli improved salt stress tolerance. Moreover, the salt stress-related genes (MdSOS2, MdSOS3, MdNHX1, MdATK2/3, MdCBL-1, MdMYB46, MdWRKY30, and MdHB-7) were more strongly down-regulated in MdGRF6-OE transgenic apple calli lines than in the WT when subjected to salt stress treatment. Taken together, these results provide new insights into the roles of 14-3-3 protein MdGRF6 in modulating salt responses in plants.

Genome-wide identification and gene expression analysis of the 14-3-3 gene family in potato (Solanum tuberosum L.)

BACKGROUND

14-3-3 proteins are essential in regulating various biological processes and abiotic stress responses in plants. Although 14-3-3 proteins have been studied in model plants such as Arabidopsis thaliana and Oryza sativa, there is a lack of research on the 14-3-3 gene family in potatoes (Solanum tuberosum L.).

RESULTS

A total of 18 14-3-3 genes encoding proteins containing a typical conserved PF00244 domain were identified by genome-wide analysis in potatoes. The St14-3-3 gene family members were unevenly distributed across the chromosomes, and gene structure analysis showed that gene length and intron number varied greatly among the members. Phylogenetic analysis of 14-3-3 proteins in potatoes and other plant species showed that they could be divided into two distinct groups (ε and non-ε). Members in the ε group tended to have similar exon-intron structures and conserved motif patterns. Promoter sequence analysis showed that the St14-3-3 gene promoters contained multiple hormone-, stress-, and light-responsive cis-regulatory elements. Synteny analysis suggested that segmental duplication events contributed to the expansion of the St14-3-3 gene family in potatoes. The observed syntenic relationships between some 14-3-3 genes from potato, Arabidopsis, and tomato suggest that they evolved from a common ancestor. RNA-seq data showed that St14-3-3 genes were expressed in all tissues of potatoes but that their expression patterns were different. qRT-PCR assays revealed that the expression levels of nearly all tested St14-3-3 genes were affected by drought, salt, and low-temperature stresses and that different St14-3-3 genes had different responses to these stresses.

CONCLUSIONS

In summary, genome-wide identification, evolutionary, and expression analyses of the 14-3-3 gene family in potato were conducted. These results provide important information for further studies on the function and regulation of St14-3-3 gene family members in potatoes.

Guard cell anion channel PbrSLAC1 regulates stomatal closure through PbrSnRK2.3 protein kinases

Stomatal pores on the leaf surface are the gateways for gas exchange between plants and the atmosphere, which is regulated mainly by the S-type anion channel SLAC1. However, the gene encoding the main S-type anion channel SLAC1 in pear and its genetic characteristics remain unknown. In this study, Pbr015894.1 was identified as the candidate for PbrSLAC1 in pear, and it was found to be expressed abundantly in leaves, particularly in the guard cells. Virus-induced gene silencing experiments indicated that stomatal closure was achieved by a change in cell turgor instigated by PbrSLAC1 channel transport of NO₃^- in pear leaves and induced by abscisic acid. Furthermore, the expression of PbrSLAC1 in Arabidopsis slac1-3 and slac1-4 rescued the defective NO₃^- transport seen in these mutants, pointing to its role in anion transport. Fluorescence microscopy suggested that PbrSLAC1 was localized in the plasma membrane, and a dual-luciferase assay system demonstrated an interaction between PbrSLAC1 and PbrSnRK2.3/2.8. Moreover, anion conductance mediated by PbrSLAC1 was activated by PbrSnRK2.3 in Xenopus laevis oocytes and the channel showed greater permeability for nitrate than chloride, sulfate, or malate ions. Taken together, these results demonstrate that PbrSLAC1, an anion channel regulated by PbrSnRK2.3, is involved in stomatal closure by mediating the efflux of NO₃^- in pear leaf.

Comprehensive Identification and Analyses of the GRF Gene Family in the Whole-Genome of Four Juglandaceae Species

The GRF gene family plays an important role in plant growth and development as regulators involved in plant hormone signaling and metabolism. However, the Juglandaceae GRF gene family remains to be studied. Here, we identified 15, 15, 19, and 20 GRF genes in J. regia, C. illinoinensis, J. sigillata, and J. mandshurica, respectively. The phylogeny shows that the Juglandaceae family GRF is divided into two subfamilies, the ε-group and the non-ε-group, and that selection pressure analysis did not detect amino acid loci subject to positive selection pressure. In addition, we found that the duplications of the Juglandaceae family GRF genes were all segmental duplication events, and a total of 79 orthologous gene pairs and one paralogous homologous gene pair were identified in four Juglandaceae families. The Ka/KS ratios between these homologous gene pairs were further analyzed, and the Ka/KS values were all less than 1, indicating that purifying selection plays an important role in the evolution of the Juglandaceae family GRF genes. The codon bias of genes in the GRF family of Juglandaceae species is weak, and is affected by both natural selection pressure and base mutation, and translation selection plays a dominant role in the mutation pressure in codon usage. Finally, expression analysis showed that GRF genes play important roles in pecan embryo development and walnut male and female flower bud development, but with different expression patterns. In conclusion, this study will serve as a rich genetic resource for exploring the molecular mechanisms of flower bud differentiation and embryo development in Juglandaceae. In addition, this is the first study to report the GRF gene family in the Juglandaceae family; therefore, our study will provide guidance for future comparative and functional genomic studies of the GRF gene family in the Juglandaceae specie.

Root Breeding in the Post-Genomics Era: From Concept to Practice in Apple

The development of rootstocks with a high-quality dwarf-type root system is a popular research topic in the apple industry. However, the precise breeding of rootstocks is still challenging, mainly because the root system is buried deep underground, roots have a complex life cycle, and research on root architecture has progressed slowly. This paper describes ideas for the precise breeding and domestication of wild apple resources and the application of key genes. The primary goal of this research is to combine the existing rootstock resources with molecular breeding and summarize the methods of precision breeding. Here, we reviewed the existing rootstock germplasm, high-quality genome, and genetic resources available to explain how wild resources might be used in modern breeding. In particular, we proposed the 'from genotype to phenotype' theory and summarized the difficulties in future breeding processes. Lastly, the genetics governing root diversity and associated regulatory mechanisms were elaborated on to optimize the precise breeding of rootstocks.

Arbuscular Mycorrhizal Fungi Enhanced Drought Resistance of Populus cathayana by Regulating the 14-3-3 Family Protein Genes

Plants can improve their resistance to a variety of stresses by forming mutualistic relationships with arbuscular mycorrhizal fungi (AMF). The 14-3-3 protein is a major regulator of the plant stress response. However, the regulation mechanism of 14-3-3 family protein genes (14-3-3s) of mycorrhizal plants coping with stress during AMF symbiosis remains unclear. Here, we analyzed the physiological changes and 14-3-3 expression profiles of Populus cathayana inoculated with AMF under different water conditions. The results showed that good colonization and symbiotic relationships with plants were formed under all water conditions (63.00% to 83.67%). Photosynthesis, peroxidase (POD) activity, and Mg and Ca content were significantly affected by drought and AMF. In addition, thirteen 14-3-3 protein genes (PcGRF1-PcGRF13) were identified by quantitative real-time PCR (qRT-PCR), of which the expression levels of PcGRF10 and PcGRF11 induced by AMF were significantly positively correlated with superoxide dismutase (SOD), POD, and sugar content, indicating that the 14-3-3s of mycorrhizal symbiotic plants may respond to drought through antioxidant and osmotic regulation. This is the first study on 14-3-3s in the symbiosis system of forest arbor plants and AMF, and it may help to further study the effects of 14-3-3s during AMF symbiosis on stresses and provide new ideas for improving mycorrhizal seedling cultivation under stress.

IMPORTANCE The 14-3-3 protein may regulate many biochemical and physiological processes under abiotic stress. Studies have shown that the 14-3-3 protein gene of AMF is not only upregulated under drought stress, but also enhances the regulation of AMF on plant drought tolerance by regulating plant signal pathways and drought response genes; however, knowledge about the biological relevance of these interactions remains limited and controversial. The precise functions of Populus cathayana 14-3-3s under drought stress remain poorly resolved and the mechanisms of action of these genes in mycorrhizae-induced drought stress are still unknown. Thus, studying the drought-resistance mechanism of the AMF symbiotic plant 14-3-3 gene is of special significance to improving the drought tolerance of the plant. Further systematic study is needed to probe the mechanism by which AMF regulates different 14-3-3 genes and their subsequent physiological effects on drought.

Overexpression of a Zea mays Brassinosteroid-Signaling Kinase Gene ZmBSK1 Confers Salt Stress Tolerance in Maize

Salinity has become a crucial environmental factor seriously restricting maize (Zea mays L.) growth, development and productivity. However, how plants respond to salt stress is still poorly understood. In this study, we report that a maize brassinosteroid-signaling kinase gene ZmBSK1 plays a significant role in salt stress response. Expression pattern analysis revealed that the transcript level of ZmBSK1 was upregulated by NaCl treatment both in maize leaves, roots, and stems. Phenotypic and physiological analysis showed that overexpression of ZmBSK1 in maize improved salt tolerance by reducing the malondialdehyde (MDA) content, the percentage of electrolyte leakage, O₂ ^- and H₂O₂ accumulation under salt stress, relying on the increases of antioxidant defense enzyme activities and proline content. qRT-PCR analysis showed that overexpression of ZmBSK1 also positively modulated the expression levels of reactive oxygen species (ROS)-scavenging and proline biosynthesis-related genes under salt stress. Moreover, immunoprecipitation-mass spectrometry (IP-MS) assay and firefly luciferase complementation imaging (LCI) assay showed that ZmBSK1 could associate with heat shock protein ZmHSP8 and 14-3-3-like protein ZmGF14-6, and their gene expression levels could be significantly induced by NaCl treatment in different maize tissues. Our findings unravel the new function of ZmBSK1 in salt stress response, which provides the theoretical bases for the improvement of maize salt resistance.

The role of 14-3-3 proteins in plant growth and response to abiotic stress

The 14-3-3 proteins widely exist in almost all plant species. They specifically recognize and interact with phosphorylated target proteins, including protein kinases, phosphatases, transcription factors and functional proteins, offering an array of opportunities for 14-3-3s to participate in the signal transduction processes. 14-3-3s are multigene families and can form homo- and heterodimers, which confer functional specificity of 14-3-3 proteins. They are widely involved in regulating biochemical and cellular processes and plant growth and development, including cell elongation and division, seed germination, vegetative and reproductive growth, and seed dormancy. They mediate plant response to environmental stresses such as salt, alkaline, osmotic, drought, cold and other abiotic stresses, partially via hormone-related signalling pathways. Although many studies have reviewed the function of 14-3-3 proteins, recent research on plant 14-3-3s has achieved significant advances. Here, we provide a comprehensive overview of the fundamental properties of 14-3-3 proteins and systematically summarize and dissect the emerging advances in understanding the roles of 14-3-3s in plant growth and development and abiotic stress responses. Some ambiguous questions about the roles of 14-3-3s under environmental stresses are reviewed. Interesting questions related to plant 14-3-3 functions that remain to be elucidated are also discussed.

Genome-Wide Identification and Expression Analysis of the 14-3-3 Gene Family in Mango (Mangifera indica L.)

Members of the Mi14-3-3 gene family interact with target proteins that are widely involved in plant hormone signal transduction and physiology-related metabolism and play important roles in plant growth, development and stress responses. In this study, 14-3-3s family members are identified by the bioinformatic analysis of the mango (Mangifera indica L.) genome. The gene structures, chromosomal distributions, genetic evolution, and expression patterns of these genes and the physical and chemical properties and conserved motifs of their proteins are analysed systematically. The results identified 16 members of the 14-3-3 genes family in the mango genome. The members were not evenly distributed across the chromosomes, and the gene structure analysis showed that the gene sequence length and intron number varied greatly among the different members. Protein sequence analysis showed that the Mi14-3-3 proteins had similar physical and chemical properties and secondary and tertiary structures, and protein subcellular localization showed that the Mi14-3-3 family proteins were localized to the nucleus. The sequence analysis of the Mi14-3-3s showed that all Mi14-3-3 proteins contain a typical conserved PFAM00244 domain, and promoter sequence analysis showed that the Mi14-3-3 promoters contain multiple hormone-, stress-, and light-responsive cis-regulatory elements. Expression analysis showed that the 14-3-3 genes were expressed in all tissues of mango, but that their expression patterns were different. Drought, salt and low temperature stresses affected the expression levels of 14-3-3 genes, and different 14-3-3 genes had different responses to these stresses. This study provides a reference for further studies on the function and regulation of Mi14-3-3 family members.

Comprehensive analysis of 14-3-3 family genes and their responses to cold and drought stress in cucumber

The 14-3-3 proteins play essential roles in regulating various biological processes and abiotic stress responses in plants. However, there have been few studies of 14-3-3 family members in cucumber. Here, we identified a total of ten 14-3-3 genes (named as CsGF14a-j) in the cucumber genome. These genes are unevenly distributed across six cucumber chromosomes, and six of them were found to be segmentally duplicated. A phylogenetic analysis of 14-3-3 proteins in cucumber and other plant species showed that they could be divided into two distinct groups (ε and non-ε). Members in the same group tend to have similar exon-intron structure and conserved motif patterns. Several hormone-, stress- and development-related cis-elements associated with transcriptional regulation were found in the promoters of CsGF14 genes. RNA-seq data showed that most CsGF14 genes have broad expression in different tissues, and some had preferential expression in specific tissues and variable expression at certain developmental stages during fruit development. Quantitative real-time PCR (qRT-PCR) results revealed that nearly all tested CsGF14 genes were significantly up-regulated under cold and drought stress at certain time points. These results provide important information about the functions of CsGF14 genes in cucumber.

Rice aquaporin OsPIP2;2 is a water-transporting facilitator in relevance to drought-tolerant responses

In rice (Oryza sativa), the PLASMA MEMBRANE INTRINSIC PROTEIN (PIP) family of aquaporin has 11 members, OsPIP1;1 to OsPIP1;3, and OsPIP2;1 to OsPIP2;8, which are hypothesized to facilitate the transport of H2O and other small compounds across cell membranes. To date, however, only OsPIP1;2, OsPIP2;1, and OsPIP2;4 have been demonstrated for substrate selectivity in their source plant (rice). In this study, OsPIP2;2 was characterized as the most efficient facilitator of H2O transport across cell membranes in comparison with the other 10 OsPIPs. In concomitant tests of all OsPIPs, four genes (OsPIP1;3, OsPIP2;1, OsPIP2;2, and OsPIP2;4) were induced to express in leaves of rice plants following a physiological drought stress, while OsPIP2;2 was expressed to the highest level. After de novo expression in frog oocytes and yeast cells, the four OsPIP proteins were localized to the plasma membranes in trimer and tetramer and displayed the activity to increase the membrane permeability to H2O. In comparison, OsPIP2;2 was most supportive to H2O import to oocytes and yeast cells. After de novo expression in tobacco protoplasts, OsPIP2;2 exceeded OsPIP1;3, OsPIP2;1, and OsPIP2;4 to support H2O transport across the plasma membranes. OsPIP2;2-mediated H2O transport was accompanied by drought-tolerant responses, including increases in concentrations of proline and polyamines, both of which are physiological markers of drought tolerance. In rice protoplasts, H2O transport and drought-tolerant responses, which included expression of marker genes of drought tolerance pathway, were considerably enhanced by OsPIP2;2 overexpression but strongly inhibited by the gene silencing. Furthermore, OsPIP2;2 played a role in maintenance of the cell membrane integrity and effectively protected rice cells from electrolyte leakage caused by the physiological drought stress. These results suggest that OsPIP2;2 is a predominant facilitator of H2O transport in relevance to drought tolerance in the plant.

Mechanistic aspects of carotenoid health benefits - where are we now?

Dietary intake and tissue levels of carotenoids have been associated with a reduced risk of several chronic diseases, including cardiovascular diseases, type 2 diabetes, obesity, brain-related diseases and some types of cancer. However, intervention trials with isolated carotenoid supplements have mostly failed to confirm the postulated health benefits. It has thereby been speculated that dosing, matrix and synergistic effects, as well as underlying health and the individual nutritional status plus genetic background do play a role. It appears that our knowledge on carotenoid-mediated health benefits may still be incomplete, as the underlying mechanisms of action are poorly understood in relation to human relevance. Antioxidant mechanisms - direct or via transcription factors such as NRF2 and NF-κB - and activation of nuclear hormone receptor pathways such as of RAR, RXR or also PPARs, via carotenoid metabolites, are the basic principles which we try to connect with carotenoid-transmitted health benefits as exemplified with described common diseases including obesity/diabetes and cancer. Depending on the targeted diseases, single or multiple mechanisms of actions may play a role. In this review and position paper, we try to highlight our present knowledge on carotenoid metabolism and mechanisms translatable into health benefits related to several chronic diseases.

NIN-like protein 7 promotes nitrate-mediated lateral root development by activating transcription of TRYPTOPHAN AMINOTRANSFERASE RELATED 2

Nitrate is essential for plant growth and development. When nitrate availability is low, plants produce more lateral roots (LRs) to seek nitrate from the soil. In this study, by DNA electrophoretic mobility shift and luciferase assays, it was showed that NIN-like protein 7 (NLP7) transcription factor activated expression of TAR2 by directly binding to its promoter. Finally, through genetic analysis, it was speculated that NLP7 regulated LR development through TAR2. In conclusion, NLP7 binds to the TAR2 promoter and activates TAR2 expression, thereby promoting nitrate-dependent LR development.

The apple 14-3-3 protein MdGRF11 interacts with the BTB protein MdBT2 to regulate nitrate deficiency-induced anthocyanin accumulation

Nitrogen is an important factor that affects plant anthocyanin accumulation. In apple, the nitrate-responsive BTB/TAZ protein MdBT2 negatively regulates anthocyanin biosynthesis. In this study, we found that MdBT2 undergoes posttranslational modifications in response to nitrate deficiency. Yeast two-hybrid, protein pull-down, and bimolecular fluorescence complementation (BiFC) assays showed that MdBT2 interacts with MdGRF11, a 14-3-3 protein; 14-3-3 proteins compose a family of highly conserved phosphopeptide-binding proteins involved in multiple physiological and biological processes. The interaction of MdGRF11 negatively regulated the stability of the MdBT2 protein via a 26S proteasome-dependent pathway, which increased the abundance of MdMYB1 proteins to activate the expression of anthocyanin biosynthesis-related genes. Taken together, the results demonstrate the critical role of 14-3-3 proteins in the regulation of nitrate deficiency-induced anthocyanin accumulation. Our results provide a novel avenue to elucidate the mechanism underlying the induction of anthocyanin biosynthesis in response to nitrate deficiency.

The apple MdCOP1-interacting protein 1 negatively regulates hypocotyl elongation and anthocyanin biosynthesis

BACKGROUND

In plants, CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) is a key negative regulator in photoperiod response. However, the biological function of COP1-interacting protein 1 (CIP1) and the regulatory mechanism of the CIP1-COP1 interaction are not fully understood.

RESULTS

Here, we identified the apple MdCIP1 gene based on the Arabidopsis AtCIP1 gene. Expression pattern analysis showed that MdCIP1 was constitutively expressed in various tissues of apple, and responded to stress and hormone signals at the transcriptional level. Ectopic expression of MdCIP1 complemented the phenotypes of the Arabidopsis cip1 mutant, and MdCIP1 inhibited anthocyanin biosynthesis in apple calli. In addition, the biochemical assay demonstrated that MdCIP1 could interact with MdCOP1 protein by their coiled-coil domain, and MdCIP1-OX/cop1-4 had a similar phenotype in photomorphogenesis with the cop1-4 mutant, suggesting that COP1 is epistatic to CIP1. Furthermore, the transient transformation assay indicated that MdCIP1 repressed anthocyanin biosynthesis in an MdCOP1-mediated pathway.

CONCLUSION

Take together, this study finds that MdCIP1 acts as a repressor in regulating hypocotyl elongation and anthocyanin biosynthesis through MdCOP1 in apple.

The BTB-TAZ protein MdBT2 negatively regulates the drought stress response by interacting with the transcription factor MdNAC143 in apple

Drought stress is a severe source of abiotic stress that can affect apple yield and quality, yet the underlying molecular mechanism of the drought stress response and the role of MdBT2 in the process remain unclear. Here, we find that MdBT2 negatively regulates the drought stress response. Both in vivo and in vitro assays indicated that MdBT2 interacted physically with and ubiquitinated MdNAC143, a member of the NAC TF family that is a positive regulator under drought stress. In addition, MdBT2 promotes the degradation of MdNAC143 via the 26S proteasome system. A series of transgenic assays in apple calli and Arabidopsis verify that MdBT2 confers susceptibility to drought stress at least in part by the regulation of MdNAC143. Overall, our findings provide new insight into the mechanism of MdBT2, which functions antagonistically to MdNAC143 in regulating drought stress by regulating the potential downstream target protein MdNAC143 for proteasomal degradation in apple.

MdbHLH130, an Apple bHLH Transcription Factor, Confers Water Stress Resistance by Regulating Stomatal Closure and ROS Homeostasis in Transgenic Tobacco

Drought is a major environmental factor that significantly limits crop yield and quality worldwide. Basic helix-loop-helix (bHLH) transcription factors have been reported to participate in the regulation of various abiotic stresses. In this study, a bHLH transcription factor in apple, MdbHLH130, which contains a highly conserved bHLH domain, was isolated and characterized. qRT-PCR and PMdbHLH130::GUS analyses showed that MdbHLH130 was notably induced in response to dehydration stress. Compared with the wild-type (WT), transgenic apple calli overexpressing MdbHLH130 displayed greater resistance to PEG6000 treatment. In contrast, the MdbHLH130-Anti lines were more sensitive to PEG6000 treatment than WT. Moreover, ectopic expression of MdbHLH130 in tobacco improved tolerance to water deficit stress, and plants exhibited higher germination rates and survival rates, longer roots, and lower ABA-induced stomatal closure and leaf water loss than the WT control. Furthermore, overexpression of MdbHLH130 in tobacco also led to lower electrolyte leakage, malondialdehyde contents, and reactive oxygen species (ROS) accumulation and upregulation of the expression of some ROS-scavenging and stress-responsive genes under water deficit stress. In addition, MdbHLH130 transgenic tobacco plants exhibited improved tolerance to oxidative stress compared with WT. In conclusion, these results indicate that MdbHLH130 acts as a positive regulator of water stress responses through modulating stomatal closure and ROS-scavenging in tobacco.

An apple long-chain acyl-CoA synthetase 2 gene enhances plant resistance to abiotic stress by regulating the accumulation of cuticular wax

Apple cuticular wax can protect plants from environmental stress, determine fruit luster and improve postharvest fruit storage quality. In recent years, dry weather, soil salinization and adverse environmental conditions have led to declines in apple fruit quality. However, few studies have reported the molecular mechanisms of apple cuticular wax biosynthesis. In this study, we identified a long-chain acyl-CoA synthetase MdLACS2 gene from apple. The MdLACS2 protein contained an AMP-binding domain and demonstrated long-chain acyl-CoA synthetase activity. MdLACS2 transgenic Arabidopsis exhibited reductions in epidermal permeability and water loss; change in the expression of genes related to cuticular wax biosynthesis, transport and transcriptional regulation; and differences in the composition and ultrastructure of cuticular wax. Moreover, the accumulation of cuticular wax enhanced the resistance of MdLACS2 transgenic plants to drought and salt stress. The main protein functional interaction networks of LACS2 were predicted, revealing a preliminary molecular regulation pathway for MdLACS2-mediated wax biosynthesis in apple. Our study provides candidate genes for breeding apple varieties and rootstocks with better fruit quality and higher stress resistance.

Identification of Phytochrome-Interacting Factor Family Members and Functional Analysis of MdPIF4 in Malus domestica

Phytochrome-interacting factors (PIFs), members of the basic helix-loop-helix transcription factor family that have been extensively investigated in Arabidopsis thaliana, play essential roles in plant growth and development. However, PIF members have not been systematically investigated in apples, a worldwide perennial woody crop of economic importance. Here, seven PIF genes were identified from the Malus × domestica reference genome. Chromosomal locations, gene structures, and phylogenetic relationships of these members were analyzed. Analysis of cis-acting elements in promoter regions of MdPIF genes indicated that various elements were related to light, abiotic stress, and plant hormone responsiveness. Subsequently, subcellular localization and transcriptional activity analysis revealed that MdPIFs were typical nuclear transcription factors with transcriptional activation ability. Expression analysis demonstrated that MdPIF genes had different gene expression patterns for various abiotic factors. Moreover, overexpressed MdPIF4 reduced the sensitivity of apple calluses to abscisic acid (ABA). Our work lays foundations for further investigation of PIF functions in plant growth and development in apples.

The role of NAC transcription factor in plant cold response

The NAC transcription factor (TF) is one of the largest families of TFs in plants and plays an important role in plant growth, development, and response to environmental stress. The structural and functional characteristics of NAC TFs have been uncovered in the past years, including sequence binding features of the DNA-binding domain located in the N-terminus and dynamic interplay between the domain located at the C-terminus and other proteins. Studies on NAC TF are increasing in number; these studies distinctly contribute to our understanding of the regulatory networks of NAC-mediated complex signaling and transcriptional reprogramming. Previous studies have indicated that NAC TFs are key regulators of the plant stress response. However, these studies have been for six years so far and mainly focused on drought and salt stress. There are relatively few reports about NAC TFs in plant cold signal pathway and no related reviews have been published. In this review article, we summarize the structural features of NAC TFs, the target genes, upstream regulators and interaction proteins of stress-responsive NAC TFs, and the roles NAC TFs play in plant cold stress signal pathway.

Regulation of phenylpropanoid biosynthesis by MdMYB88 and MdMYB124 contributes to pathogen and drought resistance in apple

MdMYB88 and MdMYB124 have been demonstrated to be responsible for lignin accumulation in apple under drought stress. In this study, using a metabolomic approach, we identified differentially accumulated phenylpropanoid and flavonoid metabolites in MdMYB88/124 transgenic RNAi plants under control and long-term drought stress conditions in apple roots. We confirmed the regulation of phenylalanine by MdMYB88 and MdMYB124 via UPLC-MS in apple roots under both control and drought conditions. Using Electrophoretic Mobility Shift Assay (EMSA) and ChIP-quantitative PCR (qPCR) analyses, we found that MdMYB88 positively regulates the MdCM2 gene, which is responsible for phenylalanine biosynthesis, through binding to its promoter region. Under long-term drought conditions, MdMYB88/124 RNAi plants consistently accumulated increased amounts of H2O2 and MDA, while MdMYB88 and MdMYB124 overexpression plants accumulated decreased amounts of H2O2 and MDA. We also examined the accumulation of metabolites in the phenylpropanoid biosynthesis pathway in the leaves of MdMYB88 and MdMYB124 transgenic apple plants after long-term drought stress. We found that metabolites responsible for plant defense, including phenylpropanoids and flavonoids, accumulated less in the RNAi plants but more in the overexpression plants under both control and drought conditions. We further demonstrated that MdMYB88/124 RNAi plants were more sensitive to Alternaria alternata f. sp. mali and Valsa mali, two pathogens that currently severely threaten apple production. In contrast, MdMYB88 and MdMYB124 overexpression plants were more tolerant to these pathogens. The cumulative results of this study provided evidence for secondary metabolite regulation by MdMYB88 and MdMYB124, further explained the molecular roles of MdMYB88 and MdMYB124 in drought resistance, and provided information concerning molecular aspects of their roles in disease resistance.

Genome-wide analysis and phosphorylation sites identification of the 14-3-3 gene family and functional characterization of MeGRF3 in cassava

The biological functionality of many members of the 14-3-3 gene family is regulated via phosphorylation at multiple amino acid residues. The specific phosphorylation-mediated regulation of these proteins during cassava root tuberization, however, is not well understood. In this study, 15 different 14-3-3 genes (designated MeGRF1 - 15) were identified within the cassava genome. Based upon evolutionary conservation and structural analyses, these cassava 14-3-3 proteins were grouped into ε and non-ε clusters. We found these 15 MeGRF genes to be unevenly distributed across the eight cassava chromosomes. When comparing the expression of these genes during different developmental stages, we found that three of these genes (MeGRF9, 12 and 15) were overexpressed at all developmental stages at 75, 104, 135, 182 and 267 days post-planting relative to the fibrous root stage, whereas two (MeGRF5 and 7) were downregulated during these same points. In addition, the expression of most MeGRF genes changed significantly in the early and middle stages of root tuberization. This suggests that these different MeGRF genes likely play distinct regulatory roles during cassava root tuberization. Subsequently, 18 phosphorylated amino acid residues were detected on nine of these MeGRF proteins. A phosphomimetic mutation at serine-65 in MeGRF3 in Arabidopsis thaliana (Arabidopsis) slightly influenced starch metabolism in these plants, and significantly affected the role of MeGRF3 in salt stress responses. Together these results indicate that 14-3-3 genes play key roles in responses to abiotic stress and the regulation of starch metabolism, offering valuable insights into the functions of these genes in cassava.

Genome-Wide Identification of Apple Ubiquitin SINA E3 Ligase and Functional Characterization of MdSINA2

SINA (Seven in absentia) proteins are a small family of ubiquitin ligases that play important roles in regulating plant growth and developmental processes as well as in responses to diverse types of biotic and abiotic stress. However, the characteristics of the apple SINA family have not been previously studied. Here, we identified 11 MdSINAs members in the apple genome based on their conserved, N-terminal RING and C-terminal SINA domains. We also reconstructed a phylogeny of these genes; characterized their chromosomal location, structure, and motifs; and identified two major groups of MdSINA genes. Subsequent qRT-PCR analyses were used to characterize the expression of MdSINA genes in various tissues and organs, and levels of expression were highest in leaves. MdSINAs were significantly induced under ABA and carbon- and nitrate-starvation treatment. Except for MdSINA1 and MdSINA7, the other MdSINA proteins could interact with each other. Moreover, MdSINA2 was found to be localized in the nucleus using Agrobacterium-mediated transient expression. Western-blot analysis showed that MdSINA2 accumulated extensively under light, decreased under darkness, and became insensitive to light when the RING domain was disrupted. Finally, ABA-hypersensitive phenotypes were confirmed by transgenic calli and the ectopic expression of MdSINA2 in Arabidopsis. In conclusion, our results suggest that MdSINA genes participate in the responses to different types of stress, and that MdSINA2 might act as a negative regulator in the ABA stress response.