Genome-wide identification and analysis of late embryogenesis abundant (LEA) genes in Prunus mume

Genome-Wide Characterization of Wholly Disordered Proteins in Arabidopsis

Intrinsically disordered proteins (IDPs) include two types of proteins: partial disordered regions (IDRs) and wholly disordered proteins (WDPs). Extensive studies focused on the proteins with IDRs, but less is known about WDPs because of their difficult-to-form folded tertiary structure. In this study, we developed a bioinformatics method for screening more than 50 amino acids in the genome level and found a total of 27 categories, including 56 WDPs, in Arabidopsis. After comparing with 56 randomly selected structural proteins, we found that WDPs possessed a more wide range of theoretical isoelectric point (PI), a more negative of Grand Average of Hydropathicity (GRAVY), a higher value of Instability Index (II), and lower values of Aliphatic Index (AI). In addition, by calculating the FCR (fraction of charged residue) and NCPR (net charge per residue) values of each WDP, we found 20 WDPs in R1 (FCR < 0.25 and NCPR < 0.25) group, 15 in R2 (0.25 ≤ FCR ≤ 0.35 and NCPR ≤ 0.35), 19 in R3 (FCR > 0.35 and NCPR ≤ 0.35), and two in R4 (FCR > 0.35 and NCPR > 0.35). Moreover, the gene expression and protein-protein interaction (PPI) network analysis showed that WDPs perform different biological functions. We also showed that two WDPs, SIS (Salt Induced Serine rich) and RAB18 (a dehydrin family protein), undergo the in vitro liquid-liquid phase separation (LLPS). Therefore, our results provide insight into understanding the biochemical characters and biological functions of WDPs in plants.

Genome-Wide Identification, Phylogenetic Evolution, and Abiotic Stress Response Analyses of the Late Embryogenesis Abundant Gene Family in the Alpine Cold-Tolerant Medicinal Notopterygium Species

Late embryogenesis abundant (LEA) proteins are a class of proteins associated with osmotic regulation and plant tolerance to abiotic stress. However, studies on the LEA gene family in the alpine cold-tolerant herb are still limited, and the phylogenetic evolution and biological functions of its family members remain unclear. In this study, we conducted genome-wide identification, phylogenetic evolution, and abiotic stress response analyses of LEA family genes in Notopterygium species, alpine cold-tolerant medicinal herbs in the Qinghai-Tibet Plateau and adjacent regions. The gene family identification analysis showed that 23, 20, and 20 LEA genes were identified in three Notopterygium species, N. franchetii, N. incisum, and N. forrestii, respectively. All of these genes can be classified into six LEA subfamilies: LEA_1, LEA_2, LEA_5, LEA_6, DHN (Dehydrin), and SMP (seed maturation protein). The LEA proteins in the three Notopterygium species exhibited significant variations in the number of amino acids, physical and chemical properties, subcellular localization, and secondary structure characteristics, primarily demonstrating high hydrophilicity, different stability, and specific subcellular distribution patterns. Meanwhile, we found that the members of the same LEA subfamily shared similar exon-intron structures and conserved motifs. Interestingly, the chromosome distributions of LEA genes in Notopterygium species were scattered. The results of the collinearity analysis indicate that the expansion of the LEA gene family is primarily driven by gene duplication. A Ka/Ks analysis showed that paralogous gene pairs were under negative selection in Notopterygium species. A promoter cis-acting element analysis showed that most LEA genes possessed multiple cis-elements connected to plant growth and development, stress response, and plant hormone signal transduction. An expression pattern analysis demonstrated the species-specific and tissue-specific expression of NinLEAs. Experiments on abiotic stress responses indicated that the NinLEAs play a crucial role in the response to high-temperature and drought stresses in N. franchetii leaves and roots. These results provide novel insights for further understanding the functions of the LEA gene family in the alpine cold-tolerant Notopterygium species and also offer a scientific basis for in-depth research on the abiotic stress response mechanisms and stress-resistant breeding.

Overexpression of AtruLEA1 from Acer truncatum Bunge Enhanced Arabidopsis Drought and Salt Tolerance by Improving ROS-Scavenging Capability

Late embryonic developmental abundant (LEA) genes play a crucial role in the response to abiotic stress and are important target genes for research on plant stress tolerance mechanisms. Acer truncatum Bunge is a promising candidate tree species for investigating the tolerance mechanism of woody plants against abiotic stress. In our previous study, AtruLEA1 was identified as being associated with seed drought tolerance. In this study, LEA1 was cloned from A. truncatum Bunge and functionally characterized. AtruLEA1 encodes an LEA protein and is located in the nucleus. Phylogenetic tree analysis revealed a recent affinity of the AtruLEA1 protein to AT3G15760.1. Overexpression of AtruLEA1 resulted in enhanced tolerance of Arabidopsis thaliana to drought and salt stress and heightened the ABA sensitivity. Compared to wild-type (WT) plants, plants with overexpressed AtruLEA1 exhibited increased activities of antioxidant enzymes under drought stress. Meanwhile, the ROS level of transgenic Arabidopsis was significantly less than that of the WT. Additionally, the stoma density and stoma openness of AtruLEA1 Arabidopsis were higher compared to those in the WT Arabidopsis under salt and drought stress conditions, which ensures that the biomass and relative water content of transgenic Arabidopsis are significantly better than those of the WT. These results indicated that AtruLEA1 was involved in salt and drought stress tolerances by maintaining ROS homeostasis, and its expression was positively regulated by abiotic stress. These results indicate a positive role of AtruLEA1 in drought and salt stress and provide theoretical evidence in the direction of cultivating resistant plants.

The cacao gene atlas: a transcriptome developmental atlas reveals highly tissue-specific and dynamically-regulated gene networks in Theobroma cacao L

BACKGROUND

Theobroma cacao, the cocoa tree, is a tropical crop grown for its highly valuable cocoa solids and fat which are the basis of a 200-billion-dollar annual chocolate industry. However, the long generation time and difficulties associated with breeding a tropical tree crop have limited the progress of breeders to develop high-yielding disease-resistant varieties. Development of marker-assisted breeding methods for cacao requires discovery of genomic regions and specific alleles of genes encoding important traits of interest. To accelerate gene discovery, we developed a gene atlas composed of a large dataset of replicated transcriptomes with the long-term goal of progressing breeding towards developing high-yielding elite varieties of cacao.

RESULTS

We describe the creation of the Cacao Transcriptome Atlas, its global characterization and define sets of genes co-regulated in highly organ- and temporally-specific manners. RNAs were extracted and transcriptomes sequenced from 123 different tissues and stages of development representing major organs and developmental stages of the cacao lifecycle. In addition, several experimental treatments and time courses were performed to measure gene expression in tissues responding to biotic and abiotic stressors. Samples were collected in replicates (3-5) to enable statistical analysis of gene expression levels for a total of 390 transcriptomes. To promote wide use of these data, all raw sequencing data, expression read mapping matrices, scripts, and other information used to create the resource are freely available online. We verified our atlas by analyzing the expression of genes with known functions and expression patterns in Arabidopsis (ACT7, LEA19, AGL16, TIP13, LHY, MYB2) and found their expression profiles to be generally similar between both species. We also successfully identified tissue-specific genes at two thresholds in many tissue types represented and a set of genes highly conserved across all tissues.

CONCLUSION

The Cacao Gene Atlas consists of a gene expression browser with graphical user interface and open access to raw sequencing data files as well as the unnormalized and CPM normalized read count data mapped to several cacao genomes. The gene atlas is a publicly available resource to allow rapid mining of cacao gene expression profiles. We hope this resource will be used to help accelerate the discovery of important genes for key cacao traits such as disease resistance and contribute to the breeding of elite varieties to help farmers increase yields.

Genome-wide identification of late embryogenesis abundant protein family and their key regulatory network in Pinus tabuliformis cold acclimation

Cold acclimation is a crucial biological process that enables conifers to overwinter safely. The late embryogenesis abundant (LEA) protein family plays a pivotal role in enhancing freezing tolerance during this process. Despite its importance, the identification, molecular functions and regulatory networks of the LEA protein family have not been extensively studied in conifers or gymnosperms. Pinus tabuliformis, a conifer with high ecological and economic values and with high-quality genome sequence, is an ideal candidate for such studies. Here, a total of 104 LEA genes were identified from P. tabuliformis, and we renamed them according to their subfamily group: PtLEA1-PtLEA92 (group LEA1-LEA6), PtSMP1-PtSMP6 (group seed maturation protein) and PtDHN1-PtDHN6 (group Dehydrin). While the sequence structure of P. tabuliformis  LEA genes are conserved, their physicochemical properties exhibit unique characteristics within different subfamily groupings. Notably, the abundance of low-temperature responsive elements in PtLEA genes was observed. Using annual rhythm and temperature gradient transcriptome data, PtLEA22 was identified as a key gene that responds to low-temperature induction while conforming to the annual cycle of cold acclimation. Overexpression of PtLEA22 enhanced Arabidopsis freezing tolerance. Furthermore, several transcription factors potentially co-expressed with PtLEA22 were validated using yeast one-hybrid and dual-luciferase assays, revealing that PtDREB1 could directly bind PtLEA22 promoter to positively regulate its expression. These findings reveal the genome-wide characterization of P. tabuliformis  LEA genes and their importance in the cold acclimation, while providing a theoretical basis for studying the molecular mechanisms of cold acclimation in conifers.

Enzyme stabilization and thermotolerance function of the intrinsically disordered LEA2 proteins from date palm

In date palm, the LEA2 genes are of abundance with sixty-two members that are nearly all ubiquitous. However, their functions and interactions with potential target molecules are largely unexplored. In this study, five date palm LEA2 genes, PdLEA2.2, PdLEA2.3, PdLEA2.4, PdLEA2.6, and PdLEA2.7 were cloned, sequenced, and three of them, PdLEA2.2, PdLEA2.3, and PdLEA2.4 were functionally characterized for their effects on the thermostability of two distinct enzymes, lactate dehydrogenase (LDH) and β-glucosidase (bglG) in vitro. Overall, PdLEA2.3 and PdLEA2.4 were moderately hydrophilic, PdLEA2.7 was slightly hydrophobic, and PdLEA2.2 and PdLEA2.6 were neither. Sequence and structure prediction indicated the presence of a stretch of hydrophobic residues near the N-terminus that could potentially form a transmembrane helix in PdLEA2.2, PdLEA2.4, PdLEA2.6 and PdLEA2.7. In addition to the transmembrane helix, secondary and tertiary structures prediction showed the presence of a disordered region followed by a stacked β-sheet region in all the PdLEA2 proteins. Moreover, three purified recombinant PdLEA2 proteins were produced in vitro, and their presence in the LDH enzymatic reaction enhanced the activity and reduced the aggregate formation of LDH under the heat stress. In the bglG enzymatic assays, PdLEA2 proteins further displayed their capacity to preserve and stabilize the bglG enzymatic activity.

Isolation of 5' regulatory region of COLD1 gene and its functional characterization through transient expression analysis in tobacco and sugarcane

Chilling Tolerant Divergence 1 (COLD1) gene consists of Golgi pH Receptor (GPHR) as well as Abscisic Acid-linked G Protein-Coupled Receptor (ABA_GPCR), which are the major transmembrane proteins in plants. This gene expression has been found to be differentially regulated, under various stress conditions, in wild Saccharum-related genera, Erianthus arundinaceus, compared to commercial sugarcane variety. In this study, Rapid Amplification of Genomic Ends (RAGE) technique was employed to isolate the 5' upstream region of COLD1 gene to gain knowledge about the underlying stress regulatory mechanism. The current study established the cis-acting elements, main promoter regions, and Transcriptional Start Site (TSS) present within the isolated 5' upstream region (Cold1P) of COLD1, with the help of specific bioinformatics techniques. Phylogenetic analysis results revealed that the isolated Cold1P promoter is closely related to the species, Sorghum bicolor. Cold1P promoter-GUS gene construct was generated in pCAMBIA 1305.1 vector that displayed a constitutive expression of the GUS reporter gene in both monocot as well as dicot plants. The histochemical GUS assay outcomes confirmed that Cold1P can drive expression in both monocot as well as dicot plants. Cold1P's activities under several abiotic stresses such as cold, heat, salt, and drought, revealed its differential expression profile in commercial sugarcane variety. The highest activity of the GUS gene was found after 24 h of cold stress, driven by the isolated Cold1P promoter. The outcomes from GUS fluorimetric assay correlated with that of the GUS expression findings. This is the first report on Cold1P isolated from the species, E. arundinaceus.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03650-8.

Genome-wide identification and expression analysis of late embryogenesis abundant (LEA) genes reveal their potential roles in somatic embryogenesis in hybrid sweetgum (Liquidambar styraciflua × Liquidambar formosana)

Late embryogenesis abundant (LEA) proteins are widely distributed in higher plants that play significant roles in embryonic development and abiotic stress response. Hybrid sweetgum is an important forest tree resource around the world, and somatic embryogenesis is an efficient way of reproduction and utilization. However, a systematic analysis of the LEA family genes in hybrid sweetgum is lacking, this is not conducive to the efficiency of its somatic embryogenesis. From the whole genome of the hybrid sweetgum, utilizing hidden Markov models, an identification of a total of 79 LEA genes was successfully conducted. They were classified into eight different groups based on their conserved domains and phylogenetic relationships, with the LsfLEA2 group of genes being the most abundant. The gene structure and sequence characteristics and chromosomal localization, as well as the physicochemical properties of LEA proteins were meticulously carried out. Analysis of the cis-acting elements shows that most of the LsfLEA genes are associated with light-responsive-elements. In addition, some genes are associated with biosynthetic pathways, such as abscisic acid response, growth hormone response, methyl jasmonate response, somatic embryogenesis, meristematic tissue expression. Furthermore, we systematically analyzed the expression patterns of hybrid sweetgum LEA genes in different stages of somatic embryogenesis and different tissues, in LEA family genes we also found significant specificity in gene expression during somatic embryogenesis. This study provides new insights into the formation of members of the LsfLEA family genes in hybrid sweetgum, while improving the understanding of the potential role of these genes in the process of hybrid sweetgum somatic embryogenesis and abiotic stress response. These results have a certain guiding significance for the future functional study of LsfLEA family genes, and provide a theoretical basis for exploring the regulatory mechanism of LsfLEA genes in the somatic embryo development stage of hybrid sweetgum.

Identification and analysis of lignin biosynthesis genes related to fruit ripening and stress response in banana (Musa acuminata L. AAA group, cv. Cavendish)

BACKGROUND

Lignin is a key component of the secondary cell wall of plants, providing mechanical support and facilitating water transport as well as having important impact effects in response to a variety of biological and abiotic stresses.

RESULTS

In this study, we identified 104 genes from ten enzyme gene families related to lignin biosynthesis in Musa acuminata genome and found the number of MaCOMT gene family was the largest, while MaC3Hs had only two members. MaPALs retained the original members, and the number of Ma4CLs in lignin biosynthesis was significantly less than that of flavonoids. Segmental duplication existed in most gene families, except for MaC3Hs, and tandem duplication was the main way to expand the number of MaCOMTs. Moreover, the expression profiles of lignin biosynthesis genes during fruit development, postharvest ripening stages and under various abiotic and biological stresses were investigated using available RNA-sequencing data to obtain fruit ripening and stress response candidate genes. Finally, a co-expression network of lignin biosynthesis genes was constructed by weighted gene co-expression network analysis to elucidate the lignin biosynthesis genes that might participate in lignin biosynthesis in banana during development and in response to stresses.

CONCLUSION

This study systematically identified the lignin biosynthesis genes in the Musa acuminata genome, providing important candidate genes for further functional analysis. The identification of the major genes involved in lignin biosynthesis in banana provides the basis for the development of strategies to improve new banana varieties tolerant to biological and abiotic stresses with high yield and high quality.

Genome-wide study and functional characterization elucidates the potential association of late embryogenesis abundant (LEA) genes with lotus seed development

Late embryogenesis abundant (LEA) proteins are extremely hydrophilic proteins imperatively associated with plant growth and development, as well as cell protection from abiotic stress. However, the genome-wide characterization of LEA gene family remains limited, especially in aquatic species such as lotus (Nelumbo spp.). Here, 57 putative LEA genes, including 28 NnLEAs and 29 NlLEAs were identified in the N.nucifera and N.lutea genomes, respectively. A total of 27 homologous LEA gene pairs were identified, indicating high degree of sequence homologies between the two Nelumbo species. Secondary structure prediction indicated high prevalence of alpha (α) helix structure among LEA proteins in the LEA_1, LEA_4, and SMP groups. Screening of putative promoter cis-elements revealed that NnLEA genes were involved in diverse biological processes. Most NnLEA genes were predominantly expressed in the late cotyledons and plumules development stages, suggesting their potential vital roles in lotus seed maturation. In addition, genes co-expressed with NnLEAs were involved in ABA signaling, seed maturation, and development processes. Overall, this study provides new insights for the in-depth understanding of the functions of NnLEA proteins in lotus seed development, and could act as a useful reference for the molecular breeding of seeds with prolonged lifespan.

Genome-Wide Characterization and Analysis of R2R3-MYB Genes Related to Fruit Ripening and Stress Response in Banana (Musa acuminata L. AAA Group, cv. 'Cavendish')

MYB is an important type of transcription factor in eukaryotes. It is widely involved in a variety of biological processes and plays a role in plant morphogenesis, growth and development, primary and secondary metabolite synthesis, and other life processes. In this study, bioinformatics methods were used to identify the R2R3-MYB transcription factor family members in the whole Musa acuminata (DH-Pahang) genome, one of the wild ancestors of banana. A total of 280 MaMYBs were obtained, and phylogenetic analysis indicated that these MaMYBs could be classified into 33 clades with MYBs from Arabidopsis thaliana. The amino acid sequences of the R2 and R3 Myb-DNA binding in all MaMYB protein sequences were quite conserved, especially Arg-12, Arg-13, Leu-23, and Leu-79. Distribution mapping results showed that 277 MaMYBs were localized on the 11 chromosomes in the Musa acuminata genome. The MaMYBs were distributed unevenly across the 11 chromosomes. More than 40.0% of the MaMYBs were located in collinear fragments, and segmental duplications likely played a key role in the expansion of the MaMYBs. Moreover, the expression profiles of MaMYBs in different fruit development and ripening stages and under various abiotic and biotic stresses were investigated using available RNA-sequencing data to obtain fruit development, ripening-specific, and stress-responsive candidate genes. Weighted gene co-expression network analysis (WGCNA) was used to analyze transcriptome data of banana from the above 11 samples. We found MaMYBs participating in important metabolic biosynthesis pathways in banana. Collectively, our results represent a comprehensive genome-wide study of the MaMYB gene family, which should be helpful in further detailed studies on MaMYBs functions related to fruit development, postharvest ripening, and the seedling response to stress in an important banana cultivar.

The LEA gene family in tomato and its wild relatives: genome-wide identification, structural characterization, expression profiling, and role of SlLEA6 in drought stress

BACKGROUND

Late embryogenesis abundant (LEA) proteins are widely distributed in higher plants and play crucial roles in regulating plant growth and development processes and resisting abiotic stress. Cultivated tomato (Solanum lycopersicum) is an important vegetable crop worldwide; however, its growth, development, yield, and quality are currently severely constrained by abiotic stressors. In contrast, wild tomato species are more tolerant to abiotic stress and can grow normally in extreme environments. The main objective of this study was to identify, characterize, and perform gene expression analysis of LEA protein families from cultivated and wild tomato species to mine candidate genes and determine their potential role in abiotic stress tolerance in tomatoes.

RESULTS

Total 60, 69, 65, and 60 LEA genes were identified in S. lycopersicum, Solanum pimpinellifolium, Solanum pennellii, and Solanum lycopersicoides, respectively. Characterization results showed that these genes could be divided into eight clusters, with the LEA_2 cluster having the most members. Most LEA genes had few introns and were non-randomly distributed on chromosomes; the promoter regions contained numerous cis-acting regulatory elements related to abiotic stress tolerance and phytohormone responses. Evolutionary analysis showed that LEA genes were highly conserved and that the segmental duplication event played an important role in evolution of the LEA gene family. Transcription and expression pattern analyses revealed different regulatory patterns of LEA genes between cultivated and wild tomato species under normal conditions. Certain S. lycopersicum LEA (SlLEA) genes showed similar expression patterns and played specific roles under different abiotic stress and phytohormone treatments. Gene ontology and protein interaction analyses showed that most LEA genes acted in response to abiotic stimuli and water deficit. Five SlLEA proteins were found to interact with 11 S. lycopersicum WRKY proteins involved in development or resistance to stress. Virus-induced gene silencing of SlLEA6 affected the antioxidant and reactive oxygen species defense systems, increased the degree of cellular damage, and reduced drought resistance in S. lycopersicum.

CONCLUSION

These findings provide comprehensive information on LEA proteins in cultivated and wild tomato species and their possible functions under different abiotic and phytohormone stresses. The study systematically broadens our current understanding of LEA proteins and candidate genes and provides a theoretical basis for future functional studies aimed at improving stress resistance in tomato.

Integrated Transcriptome and Metabolome Analysis of Color Change and Low-Temperature Response during Flowering of Prunus mume

In China, Prunus mume is a famous flowering tree that has been cultivated for 3000 years. P. mume grows in tropical and subtropical regions, and most varieties lack cold resistance; thus, it is necessary to study the low-temperature response mechanism of P. mume to expand the scope of its cultivation. We used the integrated transcriptomic and metabolomic analysis of a cold-resistant variety of P. mume 'Meiren', to identify key genes and metabolites associated with low temperatures during flowering. The 'Meiren' cultivar responded in a timely manner to temperature by way of a low-temperature signal transduction pathway. After experiencing low temperatures, the petals fade and wilt, resulting in low ornamental value. At the same time, in the cold response pathway, the activities of related transcription factors up- or downregulate genes and metabolites related to low temperature-induced proteins, osmotic regulators, protective enzyme systems, and biosynthesis and metabolism of sugars and acids. Our findings promote research on the adaptation of P. mume to low temperatures during wintering and early flowering for domestication and breeding.

Involvement of dehydrin proteins in mitigating the negative effects of drought stress in plants

Drought stress-induced crop loss has been considerably increased in recent years because of global warming and changing rainfall pattern. Natural drought-tolerant plants entail the recruitment of a variety of metabolites and low molecular weight proteins to negate the detrimental effects of drought stress. Dehydrin (DHN) proteins are one such class of proteins that accumulate in plants during drought and associated stress conditions. These proteins are highly hydrophilic and perform multifaceted roles in the protection of plant cells during drought stress conditions. Evidence gathered over the years suggests that DHN proteins impart drought stress tolerance by enhancing the water retention capacity, elevating chlorophyll content, maintaining photosynthetic machinery, activating ROS detoxification, and promoting the accumulation of compatible solutes, among others. Overexpression studies have indicated that these proteins can be effectively targeted to mitigate the negative effects of drought stress and for the development of drought stress-tolerant crops to feed the ever-growing population in the near future. In this review, we describe the mechanism of DHNs mediated drought stress tolerance in plants and their interaction with several phytohormones to provide an in-depth understanding of DHNs function.

Functional characterization of late embryogenesis abundant genes and promoters in pearl millet (Pennisetum glaucum L.) for abiotic stress tolerance

Late embryogenesis abundant (LEA) genes display distinct functions in response to abiotic stresses in plants. In pearl millet (Pennisetum glaucum L.), a total of 21 PgLEA genes were identified and classified into six groups including LEA1, LEA2, LEA3, LEA5, LEA7, and dehydrins (DHN). Open reading frames (ORFs) of PgLEAs range from 291 bp (PgLEA1-1) to 945 bp (PgLEA2-11) and distributed randomly among the seven chromosomes. Phylogenetic analysis revealed that all PgLEA proteins are closely related to sorghum LEA proteins. The PgLEAs were found to be expressed differentially under high progressive vapor pressure deficit (VPD), PgLEA7 was significantly expressed under high VPD and was selected for functional validation. In silico analysis of the PgLEA promoter regions revealed abiotic stress-specific cis-acting elements such as ABRE, CCAAT, MYBS, and LTRE. Based on the type of motifs, PgLEAPC promoter (758 bp), its deletion 1 (PgLpd1, 349 bp) and deletion 2 (PgLpd2, 125 bp) were cloned into the plant expression vector pMDC164 having the promoter-less uidA gene. All the three plant expression vectors were introduced into tobacco through Agrobacterium tumefaciens-mediated transformation to obtain T₁ and T₂ generations of transgenic plants. Based on expression of the uidA gene, tissue-specific expression was observed in mature stems, roots and seedlings of PgLEAPC and PgLpd1 carrying transgenics only. While the transgenic PgLEAPC plants displayed significantly higher uidA expression in the stem and root tissues under salt, drought, heat, and cold stresses, very low or no expression was observed in PgLpd1 and PgLpd2 transgenics under the tested stress conditions. The results of this study indicate that the complete promoter of PgLEAPC plays a role in developing abiotic stress tolerance in plants.

Late embryogenesis abundant (LEA) gene family in Salvia miltiorrhiza: identification, expression analysis, and response to drought stress

Late embryogenesis abundant (LEA) proteins play important roles in plant defense response to drought stress. However, genome-wide identification of the LEA gene family was not revealed in Salvia miltiorrhiza. In this study, 61 SmLEA genes were identified from S. miltiorrhiza and divided into 7 subfamilies according to their conserved domains and phylogenetic relationships. SmLEA genes contained the LEA conserved motifs and few introns. SmLEA genes of the same subfamilies had similar gene structures and predicted subcellular locations. Our results indicated that the promoters of SmLEA genes contained various cis-acting elements associated with abiotic stress response. In addition, RNA-seq and real-time PCR results suggested that SmLEA genes are specifically expressed in different tissue, and most SmLEA genes can be induced by drought stress. These results provide a valuable foundation for future functional investigations of SmLEA genes and drought stress-resistant breeding of S. miltiorrhiza.

Research advances in and prospects of ornamental plant genomics

The term 'ornamental plant' refers to all plants with ornamental value, which generally have beautiful flowers or special plant architectures. China is rich in ornamental plant resources and known as the "mother of gardens". Genomics is the science of studying genomes and is useful for carrying out research on genome evolution, genomic variations, gene regulation, and important biological mechanisms based on detailed genome sequence information. Due to the diversity of ornamental plants and high sequencing costs, the progress of genome research on ornamental plants has been slow for a long time. With the emergence of new sequencing technologies and a reduction in costs since the whole-genome sequencing of the first ornamental plant (Prunus mume) was completed in 2012, whole-genome sequencing of more than 69 ornamental plants has been completed in <10 years. In this review, whole-genome sequencing and resequencing of ornamental plants will be discussed. We provide analysis with regard to basic data from whole-genome studies of important ornamental plants, the regulation of important ornamental traits, and application prospects.

Characterization of LEA genes in Dendrobium officinale and one Gene in induction of callus

Late embryogenesis abundant (LEA) proteins are widely involved in plant stress responsive, while their involvement in callus formation is largest unknown. In this study, we identified and conducted expression analysis of the LEA genes from Phalaenopsis equestris and Dendrobium officinale, and characterized a LEA gene from D. officinale. A total 57 and 59 LEA genes were identified in P. equestris and D. officinale, respectively. A phylogenetic analysis showed that AtM, LEA_5 and Dehydrin groups were absent in both orchids. LEA_1 group genes were strongly expressed in seeds, significantly down-regulated in flowers, and absent in vegetative organs (leaves, stems and roots) in both orchids. Moreover, LEA_1 and LEA_4 group genes from D. officinale were abundant in the protocorm-like body stage and were dramatically up-regulated in response to abscisic acid and salinity stress. A LEA_1 gene (DoLEA43) was selected for further functional analysis. DoLEA43 protein was localized in the cytoplasm and nucleus, and its promoter contained a WUN-motif that was modulated by wounding. Overexpression of DoLEA43 in Arabidopsis enhanced callus induction, causing changes to callus formation-related genes such as WIND1. Our results indicate the involvement of LEA genes in the induction of callus, which provide insights into plant regeneration.

Genome-wide identification, phylogenetic analysis and expression profiling of the late embryogenesis-abundant (LEA) gene family in Brachypodium distachyon

Late embryogenesis-abundant (LEA) proteins are the products of an important gene family in plants that play vital roles in regulating growth and development as well as a variety of stress responses. In our study, 67 members of LEA (BdLEA) were identified in the genome of Brachypodium distachyon L. Analyses of gene structure, evolutionary relationships and protein motifs showed that the BdLEAs belonged to six subfamilies. Analyses of chromosomal locations and duplication events revealed that the 67 BdLEAs were distributed over all five chromosomes and 26 BdLEAs were identified as products of duplication events. Gene Ontology (GO) annotation results suggested that nearly 60% of BdLEAs could be involved in stress response. Furthermore, transcriptomic analysis showed that the BdLEAs were differentially expressed in nine organs and responded to low stringency of exogenous phytohormones. Subsequently, 18 BdLEAs from six subfamilies were randomly selected for quantitative real-time PCR (qRT-PCR) analysis, which showed that they were mainly expressed in the spikelets and they may preferentially respond to salt, drought and abscisic acid (ABA) stress. This study is the first to report the characteristics of the BdLEA family, providing valuable information for understanding the evolution of LEAs in the model plant B. distachyon and supporting future functional research on these proteins.

The Acer truncatum genome provides insights into nervonic acid biosynthesis

Acer truncatum (purpleblow maple) is a woody tree species that produces seeds with high levels of valuable fatty acids (especially nervonic acid). However, the lack of a complete genome sequence has limited both basic and applied research on A. truncatum. We describe a high-quality draft genome assembly comprising 633.28 Mb (contig N50 = 773.17 kb; scaffold N50 = 46.36 Mb) with at least 28 438 predicted genes. The genome underwent an ancient triplication, similar to the core eudicots, but there have been no recent whole-genome duplication events. Acer yangbiense and A. truncatum are estimated to have diverged about 9.4 million years ago. A combined genomic, transcriptomic, metabonomic, and cell ultrastructural analysis provided new insights into the biosynthesis of very long-chain monounsaturated fatty acids. In addition, three KCS genes were found that may contribute to regulating nervonic acid biosynthesis. The KCS paralogous gene family expanded to 28 members, with 10 genes clustered together and distributed in the 0.27-Mb region of pseudochromosome 4. Our chromosome-scale genomic characterization may facilitate the discovery of agronomically important genes and stimulate functional genetic research on A. truncatum. Furthermore, the data presented also offer important foundations from which to study the molecular mechanisms influencing the production of nervonic acids.

Screening of optimal reference genes for qRT-PCR and preliminary exploration of cold resistance mechanisms in Prunus mume and Prunus sibirica varieties

Prunus sibirica and Prunus mume are closely related plant species that differ in cold tolerance. Hybrids of P. sibirica and true mume, belonging to the apricot mei group, inherited strong cold resistance from P. sibirica. These materials are favourable for research on the molecular mechanisms of cold resistance. However, no suitable reference genes have been identified for analysing gene expression patterns between P. sibirica and P. mume. Ten candidate reference genes were assessed, namely, actins (ACT2-1, ACT2-2, ACT2-3, ACT2-4), protein phosphatase 2A-1 (PP2A-1), ubiquitins (UBQ2, UBQ3), ubiquitin extension protein (UBQ1) and tubulins (TUB1, TUB2), with four distinct algorithms (geNorm, NormFinder, BestKeeper and RefFinder). UBQ2 was recognized as the best reference gene in stems and buds across materials (P. sibirica; 'Xiaohong Zhusha', 'Beijing Yudie', and 'Xiao Lve' for true mume; and 'Dan Fenghou', 'Fenghou', and 'Yanxing' for apricot mei) under cold stress. In addition, the temporal and spatial expression patterns of PmCBF6 and PmLEA10 among seven varieties during winter periods were analysed using UBQ2 as a reference gene. The expression differed significantly among cultivars, which may contribute to their differences in cold tolerance. This paper confirmed the strong cold tolerance of apricot mei. And the best internal reference gene suitable for seven varieties was selected: UBQ2. Based on the above results, the expression of PmCBF6 and PmLEA10 genes during wintering in seven varieties was analysed. The molecular mechanisms of cold resistance were found to be possibly different in different varieties of P. sibirica and P. mume.

Genome-Wide Analysis of Basic Helix-Loop-Helix Transcription Factors to Elucidate Candidate Genes Related to Fruit Ripening and Stress in Banana (Musa acuminata L. AAA Group, cv. Cavendish)

The basic helix-loop-helix (bHLH) proteins are a superfamily of transcription factors (TFs) that can bind to specific DNA target sites, playing a central role in a wide range of metabolic, physiological, and developmental processes in higher organisms. However, no systemic analysis of bHLH TFs has been reported in banana, a typical climacteric fruit in tropical and subtropical regions. In our study, 259 MabHLH TF genes were identified in the genome of Musa acuminata (A genome), and phylogenetic analysis indicated that these MabHLHs could be classified into 23 subfamilies with the bHLHs from rice and Arabidopsis. The amino acid sequences of the bHLH domain in all MabHLH protein sequences were quite conserved, especially Arg-12, Arg-13, Leu-23, and Leu-79. Distribution mapping results showed that 258 MabHLHs were localized on the 11 chromosomes in the M. acuminata genome. The results indicated that 40.7% of gene duplication events were located in collinear fragments, and segmental duplications might have played a key role in the expansion of MabHLHs. Moreover, the expression profiles of MabHLHs in different fruit development and ripening stages and under various abiotic and biotic stresses were investigated using available RNA-sequencing data to obtain fruit development, ripening-specific, and stress-responsive candidate genes. Finally, a co-expression network of MabHLHs was constructed by weighted gene co-expression network analysis to elucidate the MabHLHs that might participate in important metabolic biosynthesis pathways in banana during development and the response to stress. A total of 259 MabHLHs were identified, and their sequence features, conserved domains, phylogenetic relationships, chromosomal distributions, gene duplications, expression profiles, and co-expression networks were investigated. This study systematically identified the MabHLHs in the M. acuminata genome at the genome-wide level, providing important candidate genes for further functional analysis. These findings improve our understanding of the molecular basis of developmental and stress tolerance in an important banana cultivar.

Transcriptomic Analysis of the Grapevine LEA Gene Family in Response to Osmotic and Cold Stress Reveals a Key Role for VamDHN3

Late embryogenesis abundant (LEA) proteins comprise a large family that plays important roles in the regulation of abiotic stress, however, no in-depth analysis of LEA genes has been performed in grapevine to date. In this study, we analyzed a total of 52 putative LEA genes in grapevine at the genomic and transcriptomic level, compiled expression profiles of four selected (V. amurensis) VamLEA genes under cold and osmotic stresses, and studied the potential function of the V. amurensis DEHYDRIN3 (VamDHN3) gene in grapevine callus. The 52 LEA proteins were classified into seven phylogenetic groups. RNA-seq and quantitative real-time PCR results demonstrated that a total of 16 and 23 VamLEA genes were upregulated under cold and osmotic stresses, respectively. In addition, overexpression of VamDHN3 enhanced the stability of the cell membrane in grapevine callus, suggesting that VamDHN3 is involved in osmotic regulation. These results provide fundamental knowledge for the further analysis of the biological roles of grapevine LEA genes in adaption to abiotic stress.

Genome-wide identification and characterization of late embryogenesis abundant protein-encoding gene family in wheat: Evolution and expression profiles during development and stress

Late embryogenesis abundant (LEA) proteins are involved in plant stress responses and osmotic regulation, and they are accumulated in the late embryonic stage. There have been no previous genome-wide analyses of the LEA gene family members in wheat and its close relatives. In this study, 281, 53, 151, 89, 99, and 99 LEA genes were identified in wheat (Triticum aestivum), Triticum urartu, Triticum dicoccoides, Aegilops tauschii, barley, and Brachypodium distachyon, respectively. The wheat LEA gene family (TaLEA genes) was divided into eight subfamilies according to the conserved domains. All TaLEA genes contain very few introns (<3) and they are unevenly distributed on the 21 chromosomes. We identified 39 pairs of tandem duplication genes and 9 pairs of segmental duplication genes in the wheat LEA gene family. This proved that the tandem duplication and segmental duplication played an important role in the expansion of the TaLEA gene family. According to published transcriptome data and qRT-PCR analysis, the TaLEA genes exhibit different tissue expression patterns and they are regulated by various abiotic stresses, especially salt and cold stress. This study provides a comprehensive understanding of the wheat LEA gene family.

Genome-wide identification and expression analyses of the LEA protein gene family in tea plant reveal their involvement in seed development and abiotic stress responses

Late embryogenesis abundant (LEA) proteins are widely known to be present in higher plants and are believed to play important functional roles in embryonic development and abiotic stress responses. However, there is a current lack of systematic analyses on the LEA protein gene family in tea plant. In this study, a total of 48 LEA genes were identified using Hidden Markov Model profiles in C. sinensis, and were classified into seven distinct groups based on their conserved domains and phylogenetic relationships. Genes in the CsLEA_2 group were found to be the most abundant. Gene expression analyses revealed that all the identified CsLEA genes were expressed in at least one tissue, and most had higher expression levels in the root or seed relative to other tested tissues. Nearly all the CsLEA genes were found to be involved in seed development, and thirty-nine might play an important role in tea seed maturation concurrent with dehydration. However, only sixteen CsLEA genes were involved in seed desiccation, and furthermore, most were suppressed. Additionally, forty-six CsLEA genes could be induced by at least one of the tested stress treatments, and they were especially sensitive to high temperature stress. Furthermore, it was found that eleven CsLEA genes were involved in tea plant in response to all tested abiotic stresses. Overall, this study provides new insights into the formation of CsLEA gene family members and improves our understanding on the potential roles of these genes in normal development processes and abiotic stress responses in tea plant, particularly during seed development and desiccation. These results are beneficial for future functional studies of CsLEA genes that will help preserve the recalcitrant tea seeds for a long time and genetically improve tea plant.

Genome-wide identification of and functional insights into the late embryogenesis abundant (LEA) gene family in bread wheat (Triticum aestivum)

Late embryogenesis abundant (LEA) proteins are involved in the responses and adaptation of plants to various abiotic stresses, including dehydration, salinity, high temperature, and cold. Here, we report the first comprehensive survey of the LEA gene family in “Chinese Spring” wheat (Triticum aestivum). A total of 179 TaLEA genes were identified in T. aestivum and classified into eight groups. All TaLEA genes harbored the LEA conserved motif and had few introns. TaLEA genes belonging to the same group exhibited similar gene structures and chromosomal locations. Our results revealed that most TaLEA genes contained abscisic acid (ABA)-responsive elements (ABREs) and various cis-acting elements associated with the stress response in the promoter region and were induced under ABA and abiotic stress treatments. In addition, 8 genes representing each group were introduced into E. coli and yeast to investigate the protective function of TaLEAs under heat and salt stress. TaLEAs enhanced the tolerance of E. coli and yeast to salt and heat, indicating that these proteins have protective functions in host cells under stress conditions. These results increase our understanding of LEA genes and provide robust candidate genes for future functional investigations aimed at improving the stress tolerance of wheat.

Genome-Wide Identification and Expression Profiles of Late Embryogenesis-Abundant (LEA) Genes during Grain Maturation in Wheat (Triticum aestivum L.)

Late embryogenesis-abundant (LEA) genes play important roles in plant growth and development, especially the cellular dehydration tolerance during seed maturation. In order to comprehensively understand the roles of LEA family members in wheat, we carried out a series of analyses based on the latest genome sequence of the bread wheat Chinese Spring. 121 Triticum aestivum L. LEA (TaLEA) genes, classified as 8 groups, were identified and characterized. TaLEA genes are distributed in all chromosomes, most of them with a low number of introns (≤3). Expression profiles showed that most TaLEA genes expressed specifically in grains. By qRT-PCR analysis, we confirmed that 12 genes among them showed high expression levels during late stage grain maturation in two spring wheat cultivars, Yangmai16 and Yangmai15. For most genes, the peak of expression appeared earlier in Yangmai16. Statistical analysis indicated that expression level of 8 genes in Yangmai 16 were significantly higher than Yangmai 15 at 25 days after anthesis. Taken together, our results provide more knowledge for future functional analysis and potential utilization of TaLEA genes in wheat breeding.

GmSYP24, a putative syntaxin gene, confers osmotic/drought, salt stress tolerances and ABA signal pathway

As major environment factors, drought or high salinity affect crop growth, development and yield. Transgenic approach is an effective way to improve abiotic stress tolerance of crops. In this study, we comparatively analyzed gene structures, genome location, and the evolution of syntaxin proteins containing late embryogenesis abundant (LEA2) domain. GmSYP24 was identified as a dehydration-responsive gene. Our study showed that the GmSYP24 protein was located on the cell membrane. The overexpression of GmSYP24 (GmSYP24ox) in soybean and heteroexpression of GmSYP24 (GmSYP24hx) in Arabidopsis exhibited insensitivity to osmotic/drought and high salinity. However, wild type soybean, Arabidopsis, and the mutant of GmSYP24 homologous gene of Arabidopsis were sensitive to the stresses. Under the abiotic stresses, transgenic soybean plants had greater water content and higher activities of POD, SOD compared with non-transgenic controls. And the leaf stomatal density and opening were reduced in transgenic Arabidopsis. The sensitivity to ABA was decreased during seed germination of GmSYP24ox and GmSYP24hx. GmSYP24hx induced up-regulation of ABA-responsive genes. GmSYP24ox alters the expression of some aquaporins under osmotic/drought, salt, or ABA treatment. These results demonstrated that GmSYP24 played an important role in osmotic/drought or salt tolerance in ABA signal pathway.

Insight on Rosaceae Family with Genome Sequencing and Functional Genomics Perspective

Rosaceae is one of the important families possessing a variety of diversified plant species. It includes many economically valuable crops that provide nutritional and health benefits for the human. Whole genome sequences of valuable crop plants were released in recent years. Understanding of genomics helps to decipher the plant physiology and developmental process. With the information of cultivating species and its wild relative genomes, genome sequence-based molecular markers and mapping loci for economically important traits can be used to accelerate the genome assisted breeding. Identification and characterization of disease resistant capacities and abiotic stress tolerance related genes are feasible to study across species with genome information. Further breeding studies based on the identification of gene loci for aesthetic values, flowering molecular circuit controls, fruit firmness, nonacid fruits, etc. is required for producing new cultivars with valuable traits. This review discusses the whole genome sequencing reports of Malus, Pyrus, Fragaria, Prunus, and Rosa and status of functional genomics of representative traits in individual crops.

The Role of the Late Embryogenesis-Abundant (LEA) Protein Family in Development and the Abiotic Stress Response: A Comprehensive Expression Analysis of Potato (Solanum Tuberosum)

Late embryogenesis-abundant (LEA) proteins are a large and highly diverse family believed to function in normal plant growth and development, and in protecting cells from abiotic stress. This study presents a characterisation of 74 Solanum tuberosum LEA (StLEA) proteins belonging to nine groups. StLEA genes have few introns (≤2) and are distributed on all chromosomes, occurring as gene clusters on chromosomes 1, 2, and 10. All four StASR (StLEA7 group) genes were concentrated on chromosome 4, suggesting their evolutionary conservation on one chromosome. Expression profiles of StLEA genes, in different tissues and in response to hormone and stress treatments, indicated that 71 StLEA genes had differential expression levels, of which 68 StLEA genes were differentially expressed in response to hormones and stress exposure in the potato. Continuous high expression of StASR-2, StLEA3-3, StDHN-3, StLEA2-29, and StLEA2-14 in different tissues indicated their contribution to plant development processes. StLEA2-14, StLEA2-31, StLEA3-3, StASR-1, and StDHN-1 were upregulated by six abiotic stresses, showing their tolerance to a wide spectrum of environmental stresses. Expression analysis of 17 selected StLEA genes in response to drought, salt, heavy metal, heat, and cold treatments by quantitative real-time polymerase chain reaction indicated that StLEA proteins may be involved in distinct signalling pathways. Taken together, StLEA3, StDHN, and StASR subgroup genes may be excellent resources for potato defence against environmental stresses. These results provide valuable information and robust candidate genes for future functional analysis aimed at improving the stress tolerance of the potato.

The late embryogenesis abundant gene family in tea plant (Camellia sinensis): Genome-wide characterization and expression analysis in response to cold and dehydration stress

Late embryogenesis abundant (LEA) proteins are a large and highly diverse family of polypeptides that play important roles in plant growth, development and stress responses. At present, LEA gene families have been identified and systematically characterized in many plant species. However, the LEA gene family in tea plant has not been revealed, and the biological functions of the members of this family remain unknown. In this study, 33 CsLEA genes were identified from tea plant via a genome-wide study, and they were clustered into seven groups according to analyses of their phylogenetic relationships, gene structures and protein conserved motifs. In addition, expression analysis revealed that the CsLEA genes were specifically expressed in one or more tissues and significantly induced under cold and dehydration stresses, implying that CsLEA genes play important roles in tea plant growth, development and response to cold and dehydration stresses. Furthermore, a potential transcriptional regulatory network, including DREB/CBF, MYB, bZIP, bHLH, BPC and other transcription factors, is directly associated with the expression of CsLEA genes, which may be ubiquitous and important in the above mentioned processes. This study could help to increase our understanding of CsLEA proteins and their contributions to stress tolerance in tea plant.

Genome-scale identification, classification, and tissue specific expression analysis of late embryogenesis abundant (LEA) genes under abiotic stress conditions in Sorghum bicolor L

Late embryogenesis abundant (LEA) proteins, the space fillers or molecular shields, are the hydrophilic protective proteins which play an important role during plant development and abiotic stress. The systematic survey and characterization revealed a total of 68 LEA genes, belonging to 8 families in Sorghum bicolor. The LEA-2, a typical hydrophobic family is the most abundant family. All of them are evenly distributed on all 10 chromosomes and chromosomes 1, 2, and 3 appear to be the hot spots. Majority of the S. bicolor LEA (SbLEA) genes are intron less or have fewer introns. A total of 22 paralogous events were observed and majority of them appear to be segmental duplications. Segmental duplication played an important role in SbLEA-2 family expansion. A total of 12 orthologs were observed with Arabidopsis and 13 with Oryza sativa. Majority of them are basic in nature, and targeted by chloroplast subcellular localization. Fifteen miRNAs targeted to 25 SbLEAs appear to participate in development, as well as in abiotic stress tolerance. Promoter analysis revealed the presence of abiotic stress-responsive DRE, MYB, MYC, and GT1, biotic stress-responsive W-Box, hormone-responsive ABA, ERE, and TGA, and development-responsive SKn cis-elements. This reveals that LEA proteins play a vital role during stress tolerance and developmental processes. Using microarray data, 65 SbLEA genes were analyzed in different tissues (roots, pith, rind, internode, shoot, and leaf) which show clear tissue specific expression. qRT-PCR analysis of 23 SbLEA genes revealed their abundant expression in various tissues like roots, stems and leaves. Higher expression was noticed in stems compared to roots and leaves. Majority of the SbLEA family members were up-regulated at least in one tissue under different stress conditions. The SbLEA3-2 is the regulator, which showed abundant expression under diverse stress conditions. Present study provides new insights into the formation of LEAs in S. bicolor and to understand their role in developmental processes under stress conditions, which may be a valuable source for future research.

DNA Methylation Analysis of Dormancy Release in Almond (Prunus dulcis) Flower Buds Using Epi-Genotyping by Sequencing

DNA methylation and histone post-translational modifications have been described as epigenetic regulation mechanisms involved in developmental transitions in plants, including seasonal changes in fruit trees. In species like almond (Prunus dulcis (Mill.) D.A: Webb), prolonged exposure to cold temperatures is required for dormancy release and flowering. Aiming to identify genomic regions with differential methylation states in response to chill accumulation, we carried out Illumina reduced-representation genome sequencing on bisulfite-treated DNA from floral buds. To do this, we analyzed almond genotypes with different chilling requirements and flowering times both before and after dormancy release for two consecutive years. The study was performed using epi-Genotyping by Sequencing (epi-GBS). A total of 7317 fragments were sequenced and the samples compared. Out of these fragments, 677 were identified as differentially methylated between the almond genotypes. Mapping these fragments using the Prunus persica (L.) Batsch v.2 genome as reference provided information about coding regions linked to early and late flowering methylation markers. Additionally, the methylation state of ten gene-coding sequences was found to be linked to the dormancy release process.

DNA Methylation Analysis of Dormancy Release in Almond (Prunus dulcis) Flower Buds Using Epi-Genotyping by Sequencing

DNA methylation and histone post-translational modifications have been described as epigenetic regulation mechanisms involved in developmental transitions in plants, including seasonal changes in fruit trees. In species like almond (Prunus dulcis (Mill.) D.A: Webb), prolonged exposure to cold temperatures is required for dormancy release and flowering. Aiming to identify genomic regions with differential methylation states in response to chill accumulation, we carried out Illumina reduced-representation genome sequencing on bisulfite-treated DNA from floral buds. To do this, we analyzed almond genotypes with different chilling requirements and flowering times both before and after dormancy release for two consecutive years. The study was performed using epi-Genotyping by Sequencing (epi-GBS). A total of 7317 fragments were sequenced and the samples compared. Out of these fragments, 677 were identified as differentially methylated between the almond genotypes. Mapping these fragments using the Prunus persica (L.) Batsch v.2 genome as reference provided information about coding regions linked to early and late flowering methylation markers. Additionally, the methylation state of ten gene-coding sequences was found to be linked to the dormancy release process.

Identification of water use efficiency related genes in 'Garnem' almond-peach rootstock using time-course transcriptome analysis

Drought is one of the main abiotic stresses with far-reaching ecological and socioeconomic impacts, especially in perennial food crops such as Prunus. There is an urgent need to identify drought resilient rootstocks that can adapt to changes in water availability. In this study, we tested the hypothesis that PEG-induced water limitation stress will simulate drought conditions and drought-related genes, including transcription factors (TFs), will be differentially expressed in response to this stress. 'Garnem' genotype, an almond × peach hybrid [P. amygdalus Batsch, syn P. dulcis (Mill.) x P. persica (L.) Batsch] was exposed to PEG-6000 solution, and a time-course transcriptome analysis of drought-stressed roots was performed at 0, 2 and 24 h time points post-stress. Transcriptome analysis resulted in the identification of 12,693 unique differentially expressed contigs (DECs) at the 2 h time point, and 7,705 unique DECs at the 24 h time point after initiation of the drought treatment. Interestingly, three drought-induced genes, directly related to water use efficiency (WUE) namely, ERF023 TF; LRR receptor-like serine/threonine-kinase ERECTA; and NF-YB3 TF, were found induced under stress. The RNAseq results were validated with quantitative RT-PCR analysis of eighteen randomly selected differentially expressed contigs (DECs). Pathway analysis in the present study provides valuable information regarding metabolic events that occur during stress-induced signalling in 'Garnem' roots. This information is expected to be useful in understanding the potential mechanisms underlying drought stress responses and drought adaptation strategies in Prunus species.

Whole Genome Analysis of Cyclin Dependent Kinase (CDK) Gene Family in Cotton and Functional Evaluation of the Role of CDKF4 Gene in Drought and Salt Stress Tolerance in Plants

Cotton (Gossypium spp.) is the number one crop cultivated for fiber production and the cornerstone of the textile industry. Drought and salt stress are the major abiotic stresses, which can have a huge economic impact on cotton production; this has been aggravated with continued climate change, and compounded by pollution. Various survival strategies evolved by plants include the induction of various stress responsive genes, such as cyclin dependent kinases (CDKs). In this study, we performed a whole-genome identification and analysis of the CDK gene family in cotton. We identified 31, 12, and 15 CDK genes in G. hirsutum, G. arboreum, and G. raimondii respectively, and they were classified into 6 groups. CDK genes were distributed in 15, 10, and 9 linkage groups of AD, D, and A genomes, respectively. Evolutionary analysis revealed that segmental types of gene duplication were the primary force underlying CDK genes expansion. RNA sequence and RT-qPCR validation revealed that Gh_D12G2017 (CDKF4) was strongly induced by drought and salt stresses. The transient expression of Gh_D12G2017-GFP fusion protein in the protoplast showed that Gh_D12G2017 was localized in the nucleus. The transgenic Arabidopsis lines exhibited higher concentration levels of the antioxidant enzymes measured, including peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) concentrations under drought and salt stress conditions with very low levels of oxidants. Moreover, cell membrane stability (CMS), excised leaf water loss (ELWL), saturated leaf weight (SLW), and chlorophyll content measurements showed that the transgenic Arabidopsis lines were highly tolerant to either of the stress factors compared to their wild types. Moreover, the expression of the stress-related genes was also significantly up-regulated in Gh_D12G2017(CDKF4) transgenic Arabidopsis plants under drought and salt conditions. We infer that CDKF-4s and CDKG-2s might be the primary regulators of salt and drought responses in cotton.

Cotton Late Embryogenesis Abundant (LEA2) Genes Promote Root Growth and Confer Drought Stress Tolerance in Transgenic Arabidopsis thaliana

Late embryogenesis abundant (LEA) proteins play key roles in plant drought tolerance. In this study, 157, 85 and 89 candidate LEA2 proteins were identified in G. hirsutum, G. arboreum and G. raimondii respectively. LEA2 genes were classified into 6 groups, designated as group 1 to 6. Phylogenetic tree analysis revealed orthologous gene pairs within the cotton genome. The cotton specific LEA2 motifs identified were E, R and D in addition to Y, K and S motifs. The genes were distributed on all chromosomes. LEA2s were found to be highly enriched in non-polar, aliphatic amino acid residues, with leucine being the highest, 9.1% in proportion. The miRNA, ghr-miR827a/b/c/d and ghr-miR164 targeted many genes are known to be drought stress responsive. Various stress-responsive regulatory elements, ABA-responsive element (ABRE), Drought-responsive Element (DRE/CRT), MYBS and low-temperature-responsive element (LTRE) were detected. Most genes were highly expressed in leaves and roots, being the primary organs greatly affected by water deficit. The expression levels were much higher in G. tomentosum as opposed to G. hirsutum. The tolerant genotype had higher capacity to induce more of LEA2 genes. Over expression of the transformed gene Cot_AD24498 showed that the LEA2 genes are involved in promoting root growth and in turn confers drought stress tolerance. We therefore infer that Cot_AD24498, CotAD_20020, CotAD_21924 and CotAD_59405 could be the candidate genes with profound functions under drought stress in upland cotton among the LEA2 genes. The transformed Arabidopsis plants showed higher tolerance levels to drought stress compared to the wild types. There was significant increase in antioxidants, catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) accumulation, increased root length and significant reduction in oxidants, Hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) concentrations in the leaves of transformed lines under drought stress condition. This study provides comprehensive analysis of LEA2 proteins in cotton thus forms primary foundation for breeders to utilize these genes in developing drought tolerant genotypes.

Characterization of the late embryogenesis abundant (LEA) proteins family and their role in drought stress tolerance in upland cotton

Background

Late embryogenesis abundant (LEA) proteins are large groups of hydrophilic proteins with major role in drought and other abiotic stresses tolerance in plants. In-depth study and characterization of LEA protein families have been carried out in other plants, but not in upland cotton. The main aim of this research work was to characterize the late embryogenesis abundant (LEA) protein families and to carry out gene expression analysis to determine their potential role in drought stress tolerance in upland cotton. Increased cotton production in the face of declining precipitation and availability of fresh water for agriculture use is the focus for breeders, cotton being the backbone of textile industries and a cash crop for many countries globally.

Results

In this work, a total of 242, 136 and 142 LEA genes were identified in G. hirsutum, G. arboreum and G. raimondii respectively. The identified genes were classified into eight groups based on their conserved domain and phylogenetic tree analysis. LEA 2 were the most abundant, this could be attributed to their hydrophobic character. Upland cotton LEA genes have fewer introns and are distributed in all chromosomes. Majority of the duplicated LEA genes were segmental. Syntenic analysis showed that greater percentages of LEA genes are conserved. Segmental gene duplication played a key role in the expansion of LEA genes. Sixty three miRNAs were found to target 89 genes, such as miR164, ghr-miR394 among others. Gene ontology analysis revealed that LEA genes are involved in desiccation and defense responses. Almost all the LEA genes in their promoters contained ABRE, MBS, W-Box and TAC-elements, functionally known to be involved in drought stress and other stress responses. Majority of the LEA genes were involved in secretory pathways. Expression profile analysis indicated that most of the LEA genes were highly expressed in drought tolerant cultivars Gossypium tomentosum as opposed to drought susceptible, G. hirsutum. The tolerant genotypes have a greater ability to modulate genes under drought stress than the more susceptible upland cotton cultivars.

Conclusion

The finding provides comprehensive information on LEA genes in upland cotton, G. hirsutum and possible function in plants under drought stress.

Electronic supplementary material

The online version of this article (10.1186/s12863-017-0596-1) contains supplementary material, which is available to authorized users.

Characterization of the late embryogenesis abundant (LEA) proteins family and their role in drought stress tolerance in upland cotton

BACKGROUND

Late embryogenesis abundant (LEA) proteins are large groups of hydrophilic proteins with major role in drought and other abiotic stresses tolerance in plants. In-depth study and characterization of LEA protein families have been carried out in other plants, but not in upland cotton. The main aim of this research work was to characterize the late embryogenesis abundant (LEA) protein families and to carry out gene expression analysis to determine their potential role in drought stress tolerance in upland cotton. Increased cotton production in the face of declining precipitation and availability of fresh water for agriculture use is the focus for breeders, cotton being the backbone of textile industries and a cash crop for many countries globally.

RESULTS

In this work, a total of 242, 136 and 142 LEA genes were identified in G. hirsutum, G. arboreum and G. raimondii respectively. The identified genes were classified into eight groups based on their conserved domain and phylogenetic tree analysis. LEA 2 were the most abundant, this could be attributed to their hydrophobic character. Upland cotton LEA genes have fewer introns and are distributed in all chromosomes. Majority of the duplicated LEA genes were segmental. Syntenic analysis showed that greater percentages of LEA genes are conserved. Segmental gene duplication played a key role in the expansion of LEA genes. Sixty three miRNAs were found to target 89 genes, such as miR164, ghr-miR394 among others. Gene ontology analysis revealed that LEA genes are involved in desiccation and defense responses. Almost all the LEA genes in their promoters contained ABRE, MBS, W-Box and TAC-elements, functionally known to be involved in drought stress and other stress responses. Majority of the LEA genes were involved in secretory pathways. Expression profile analysis indicated that most of the LEA genes were highly expressed in drought tolerant cultivars Gossypium tomentosum as opposed to drought susceptible, G. hirsutum. The tolerant genotypes have a greater ability to modulate genes under drought stress than the more susceptible upland cotton cultivars.

CONCLUSION

The finding provides comprehensive information on LEA genes in upland cotton, G. hirsutum and possible function in plants under drought stress.

Genome-wide identification and expression analysis of the B-box gene family in the Apple (Malus domestica Borkh.) genome

The B-box proteins (BBXs) are a family of zinc finger proteins containing one/two B-box domain(s). Compared with intensive studies of animal BBXs, investigations of the plant BBX family are limited, though some specific plant BBXs have been demonstrated to act as transcription factors in the regulation of flowering and photomorphogenesis. In this study, using a global search of the apple (Malus domestica Borkh.) genome, a total of 64 members of BBX (MdBBX) were identified. All the MdBBXs were divided into five groups based on the phylogenetic relationship, numbers of B-boxes contained and whether there was with an additional CCT domain. According to the characteristics of organ-specific expression, MdBBXs were divided into three groups based on the microarray information. An analysis of cis-acting elements showed that elements related to the stress response were prevalent in the promoter sequences of most MdBBXs. Twelve MdBBX members from different groups were randomly selected and exposed to abiotic stresses. Their expressions were up-regulated to some extent in the roots and leaves. Six among 12 MdBBXs were sensitive to osmotic pressure, salt, cold stress and exogenous abscisic acid treatment, with their expressions enhanced more than 20-fold. Our results suggested that MdBBXs may take part in response to abiotic stress.

Evolution analysis of Dof transcription factor family and their expression in response to multiple abiotic stresses in Malus domestica

As a family of transcription factors, DNA binding with one figure (Dof) proteins play important roles in various biological processes in plants. Here, a total of 60 putative apple (Malus domestica) Dof genes (MdDof) were identified and mapped to different chromosomes. Chromosomal distribution and synteny analysis indicated that the expansion of the MdDof genes came primarily from segmental and duplication events, and from whole genome duplication, which lead to more Dof members in apples than in other plants. All 60 MdDof genes were classified into thirteen groups, according to multiple sequence alignment and the phylogenetic tree constructed of Dof genes from apple, peach (Prunus persica), Arabidopsis and rice. Within each group, the members shared a similar exon/intron and motif compositions, although the sizes of the MdDof genes and encoding proteins were quite different. Several Dof genes from the apple and peach were identified to be homologues based on their close synteny relationship, which suggested that these genes bear similar functions. Half of the MdDof genes were randomly selected to determine their responses to different stresses. The majority of MdDof genes were quite sensitive to PEG, NaCl, cold and exogenous ABA treatment. Our results suggested that MdDof family members may play important roles in plant tolerance to abiotic stress.

Genome-wide identification and comparative expression analysis of LEA genes in watermelon and melon genomes

Late embryogenesis abundant (LEA) proteins are large and diverse group of polypeptides which were first identified during seed dehydration and then in vegetative plant tissues during different stress responses. Now, gene family members of LEA proteins have been detected in various organisms. However, there is no report for this protein family in watermelon and melon until this study. A total of 73 LEA genes from watermelon (ClLEA) and 61 LEA genes from melon (CmLEA) were identified in this comprehensive study. They were classified into four and three distinct clusters in watermelon and melon, respectively. There was a correlation between gene structure and motif composition among each LEA groups. Segmental duplication played an important role for LEA gene expansion in watermelon. Maximum gene ontology of LEA genes was observed with poplar LEA genes. For evaluation of tissue specific expression patterns of ClLEA and CmLEA genes, publicly available RNA-seq data were analyzed. The expression analysis of selected LEA genes in root and leaf tissues of drought-stressed watermelon and melon were examined using qRT-PCR. Among them, ClLEA-12-17-46 genes were quickly induced after drought application. Therefore, they might be considered as early response genes for water limitation conditions in watermelon. In addition, CmLEA-42-43 genes were found to be up-regulated in both tissues of melon under drought stress. Our results can open up new frontiers about understanding of functions of these important family members under normal developmental stages and stress conditions by bioinformatics and transcriptomic approaches.

Overexpression of Prunus mume Dehydrin Genes in Tobacco Enhances Tolerance to Cold and Drought

Dehydrins, known as group 2 or D-11 family late-embryogenesis-abundant (LEA) proteins, play important roles in plant growth and stress tolerance. Six dehydrin genes were previously identified from the genome of Prunus mume. In this study, five of them (PmLEA8, PmLEA10, PmLEA19, PmLEA20, and PmLEA29) were cloned from cold-resistant P. mume 'Beijingyudie'. Real-time RT-PCR analysis indicated that all these genes could be up-regulated by one or several treatments (ABA, SA, low temperature, high temperature, PEG, and NaCl treatments). The results of spot assay demonstrated that the expression of all these dehydrins, except PmLEA8, conferred improved osmotic and freezing-resistance to the recombinant Escherichia coli. So four dehydrin genes, PmLEA10, PmLEA19, PmLEA20 and PmLEA29 were chosen for individual over-expression in tobacco plants. The transgenic tobacco plants showed lower relative content of malondialdehyde, relative electrolyte leakage and higher relative content of water than control plants when exposed to cold and drought stress. These results demonstrated that PmLEAs were involved in plant responses to cold and drought.

Functional insights into the late embryogenesis abundant (LEA) protein family from Dendrobium officinale (Orchidaceae) using an Escherichia coli system

Late embryogenesis abundant (LEA) proteins, a diverse family, accumulate during seed desiccation in the later stages of embryogenesis. LEA proteins are associated with tolerance to abiotic stresses, such as drought, salinity and high or cold temperature. Here, we report the first comprehensive survey of the LEA gene family in Dendrobium officinale, an important and widely grown medicinal orchid in China. Based on phylogenetic relationships with the complete set of Arabidopsis and Oryza LEA proteins, 17 genes encoding D. officinale LEAs (DofLEAs) were identified and their deduced proteins were classified into seven groups. The motif composition of these deduced proteins was correlated with the gene structure found in each LEA group. Our results reveal the DofLEA genes are widely distributed and expressed in tissues. Additionally, 11 genes from different groups were introduced into Escherichia coli to assess the functions of DofLEAs. Expression of 6 and 7 DofLEAs in E. coli improved growth performance compared with the control under salt and heat stress, respectively. Based on qPCR data, all of these genes were up-regulated in various tissues following exposure to salt and heat stresses. Our results suggest that DofLEAs play an important role in responses to abiotic stress.

Genome-wide investigation and expression analyses of the pentatricopeptide repeat protein gene family in foxtail millet

BACKGROUND

Pentatricopeptide repeat (PPR) proteins are encoded by a large gene family of approximately 450 members in Arabidopsis and 477 in rice, which characterized by tandem repetitions of a degenerate 35 amino acid characteristic sequence motifs. A large majority of the PPR genes in the higher plants are localized in organelles. Their functions remain as yet largely unknown. The majority of characterized PPR proteins have been found to function in modulating the expression plastid and mitochondrial genes in plants.

RESULTS

Here, a genome-wide identification and comparison of the PPR genes from 5 organisms was performed, including the moss Physcomitrella patens, the lycophyte Selaginella moellendorffii, the eudicot Arabidopsis, and the monocots rice and foxtail millet. It appears that the expansion of this gene family prior to the divergence of the euphyllophytes and the lycophytes in land plants. The duplication and divergence rates of the foxtail millet PPR genes (SiPPRs) showed that the expansion period of this gene family around 400 Mya, and indicated that genome segmental duplication was very likely the primary mechanism underlying the expansion of the PPR gene family in vascular plants. An analysis of a complete set of SiPPR genes/proteins that included classification, chromosomal location, orthologous relationships, duplication analysis, and auxiliary motifs is presented. Expression analysis of the SiPPR genes under stress conditions revealed that the expression of 24 SiPPR genes was responsive to abiotic stress. Subcellular localization analysis of 11 PPR proteins indicated that 5 proteins were localized to chloroplasts, that 4 were localized to mitochondria, and that 2 were localized to the cytoplasm.

CONCLUSIONS

Our results contribute to a more comprehensive understanding the roles of PPR proteins and will be useful in the prioritization of particular PPR proteins for subsequent functional validation studies in foxtail millet.

Transcriptome analysis of seed dormancy after rinsing and chilling in ornamental peaches (Prunus persica (L.) Batsch)

Background

Ornamental peaches cv. ‘Yaguchi’ (Prunus persica (L.) Batsch) can be propagated via seeds. The establishment of efficient seed treatments for early germination and seedling growth is required to shorten nursery and breeding periods. It is important, therefore, to identify potential candidate genes responsible for the effects of rinsing and chilling on seed germination. We hypothesized that longer rinsing combined with chilling of seeds can alter the genes expression in related to dormancy and then raise the germination rate in the peach. To date, most molecular studies in peaches have involved structural genomics, and few transcriptome studies of seed germination have been conducted. In this study, we investigated the function of key seed dormancy-related genes using next-generation sequencing to profile the transcriptomes involved in seed dormancy in peaches. De novo assembly and analysis of the transcriptome identified differentially expressed and unique genes present in this fruit.

Results

De novo RNA-sequencing of peach was performed using the Illumina Miseq 2000 system. Paired-end sequence from mRNAs generated high quality sequence reads (9,049,964, 10,026,362 and 10,101,918 reads) from ‘Yaguchi’ peach seeds before rinsed (BR) and after rinsed for 2 or 7 days with a chilling period of 4 weeks (termed 2D4W and 7D4W), respectively. The germination rate of 7D4W was significantly higher than that of 2D4W. In total, we obtained 51,366 unique sequences. Differential expression analysis identified 7752, 8469 and 506 differentially expressed genes from BR vs 2D4W, BR vs 7D4W and 2D4W vs 7D4W libraries respectively, filtered based on p-value and an adjusted false discovery rate of less than 0.05. This study identified genes associated with the rinsing and chilling process that included those associated with phytohormones, the stress response and transcription factors. 7D4W treatment downregulated genes involved in ABA synthesis, catabolism and signaling pathways, which eventually suppressed abscisic acid activity and consequently promoted germination and seedling growth. Stress response genes were also downregulated by the 7D4W treatment, suggesting that this treatment released seeds from endodormancy. Transcription factors were upregulated by the BR and 2D4W treatment, suggesting that they play important roles in maintaining seed dormancy.

Conclusions

This work indicated that longer rinsing combined with chilling affects gene expression and germination rate, and identified potential candidate genes responsible for dormancy progression in seeds of ‘Yaguchi’ peach. The results could be used to develop breeding programs and will aid future functional genomic research in peaches and other fruit trees.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2973-y) contains supplementary material, which is available to authorized users.

New features of desiccation tolerance in the lichen photobiont Trebouxia gelatinosa are revealed by a transcriptomic approach

Trebouxia is the most common lichen-forming genus of aero-terrestrial green algae and all its species are desiccation tolerant (DT). The molecular bases of this remarkable adaptation are, however, still largely unknown. We applied a transcriptomic approach to a common member of the genus, T. gelatinosa, to investigate the alteration of gene expression occurring after dehydration and subsequent rehydration in comparison to cells kept constantly hydrated. We sequenced, de novo assembled and annotated the transcriptome of axenically cultured T. gelatinosa by using Illumina sequencing technology. We tracked the expression profiles of over 13,000 protein-coding transcripts. During the dehydration/rehydration cycle c. 92 % of the total protein-coding transcripts displayed a stable expression, suggesting that the desiccation tolerance of T. gelatinosa mostly relies on constitutive mechanisms. Dehydration and rehydration affected mainly the gene expression for components of the photosynthetic apparatus, the ROS-scavenging system, Heat Shock Proteins, aquaporins, expansins, and desiccation related proteins (DRPs), which are highly diversified in T. gelatinosa, whereas Late Embryogenesis Abundant Proteins were not affected. Only some of these phenomena were previously observed in other DT green algae, bryophytes and resurrection plants, other traits being distinctive of T. gelatinosa, and perhaps related to its symbiotic lifestyle. Finally, the phylogenetic inference extended to DRPs of other chlorophytes, embryophytes and bacteria clearly pointed out that DRPs of chlorophytes are not orthologous to those of embryophytes: some of them were likely acquired through horizontal gene transfer from extremophile bacteria which live in symbiosis within the lichen thallus.