Expressional diversity of wheat nsLTP genes: evidence of subfunctionalization via cis-regulatory divergence

Root and Leaf Anatomy, Ion Accumulation, and Transcriptome Pattern under Salt Stress Conditions in Contrasting Genotypes of Sorghum bicolor

Roots from salt-susceptible ICSR-56 (SS) sorghum plants display metaxylem elements with thin cell walls and large diameter. On the other hand, roots with thick, lignified cell walls in the hypodermis and endodermis were noticed in salt-tolerant CSV-15 (ST) sorghum plants. The secondary wall thickness and number of lignified cells in the hypodermis have increased with the treatment of sodium chloride stress to the plants (STN). Lignin distribution in the secondary cell wall of sclerenchymatous cells beneath the lower epidermis was higher in ST leaves compared to the SS genotype. Casparian thickenings with homogenous lignin distribution were observed in STN roots, but inhomogeneous distribution was evident in SS seedlings treated with sodium chloride (SSN). Higher accumulation of K⁺ and lower Na⁺ levels were noticed in ST compared to the SS genotype. To identify the differentially expressed genes among SS and ST genotypes, transcriptomic analysis was carried out. Both the genotypes were exposed to 200 mM sodium chloride stress for 24 h and used for analysis. We obtained 70 and 162 differentially expressed genes (DEGs) exclusive to SS and SSN and 112 and 26 DEGs exclusive to ST and STN, respectively. Kyoto Encyclopaedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analysis unlocked the changes in metabolic pathways in response to salt stress. qRT-PCR was performed to validate 20 DEGs in each SSN and STN sample, which confirms the transcriptomic results. These results surmise that anatomical changes and higher K⁺/Na⁺ ratios are essential for mitigating salt stress in sorghum apart from the genes that are differentially up- and downregulated in contrasting genotypes.

Molecular Dissection of TaLTP1 Promoter Reveals Functional Cis-Elements Regulating Epidermis-Specific Expression

Plant epidermis serves important functions in shoot growth, plant defense and lipid metabolism, though mechanisms of related transcriptional regulation are largely unknown. Here, we identified cis-elements specific to shoot epidermis expression by dissecting the promoter of Triticum aestivum lipid transfer protein 1 (TaLTP1). A preliminary promoter deletion analysis revealed that a truncated fragment within 400 bp upstream from the translation start site was sufficient to confer conserved epidermis-specific expression in transgenic Brachypodium distachyon and Arabidopsis thaliana. Further, deletion or mutation of a GC(N4)GGCC motif at position -380 bp caused a loss of expression in pavement cells. With an electrophoretic mobility shift assay (EMSA) and transgenic reporter assay, we found that a light-responsive CcATC motif at position -268 bp was also involved in regulating pavement cell-specific expression that is evolutionary conserved. Moreover, expression specific to leaf trichome cells was found to be independently regulated by a CCaacAt motif at position -303 bp.

Genomic Identification and Comparative Expansion Analysis of the Non-Specific Lipid Transfer Protein Gene Family in Gossypium

Plant non-specific lipid transfer proteins (nsLTPs) are involved in many biological processes. In this study, 51, 47 and 91 nsLTPs were identified in Gossypium arboreum, G. raimondii and their descendant allotetraploid G. hirsutum, respectively. All the nsLTPs were phylogenetically divided into 8 distinct subfamilies. Besides, the recent duplication, which is considered cotton-specific whole genome duplication, may have led to nsLTP expansion in Gossypium. Both tandem and segmental duplication contributed to nsLTP expansion in G. arboreum and G. hirsutum, while tandem duplication was the dominant pattern in G. raimondii. Additionally, the interspecific orthologous gene pairs in Gossypium were identified. Some GaLTPs and GrLTPs lost their orthologs in the A_t and D_t subgenomes, respectively, of G. hirsutum. The distribution of these GrLTPs and GaLTPs within each subfamily was complementary, suggesting that the loss and retention of nsLTPs in G. hirsutum might not be random. Moreover, the nsLTPs in the A_t and D_t subgenomes might have evolved symmetrically. Furthermore, both intraspecific and interspecific orthologous genes showed considerable expression variation, suggesting that their functions were strongly differentiated. Our results lay an important foundation for expansion and evolutionary analysis of the nsLTP family in Gossypium, and advance nsLTP studies in other plants, especially polyploid plants.

Lipid transfer proteins: classification, nomenclature, structure, and function

The non-specific lipid transfer proteins (LTPs) constitute a large protein family found in all land plants. They are small proteins characterized by a tunnel-like hydrophobic cavity, which makes them suitable for binding and transporting various lipids. The LTPs are abundantly expressed in most tissues. In general, they are synthesized with an N-terminal signal peptide that localizes the protein to spaces exterior to the plasma membrane. The in vivo functions of LTPs are still disputed, although evidence has accumulated for a role in the synthesis of lipid barrier polymers, such as cuticular waxes, suberin, and sporopollenin. There are also reports suggesting that LTPs are involved in signaling during pathogen attacks. LTPs are considered as key proteins for the plant's survival and colonization of land. In this review, we aim to present an overview of the current status of LTP research and also to discuss potential future applications of these proteins. We update the knowledge on 3D structures and lipid binding and review the most recent data from functional investigations, such as from knockout or overexpressing experiments. We also propose and argument for a novel system for the classification and naming of the LTPs.

Response of Arabidopsis thaliana Roots with Altered Lipid Transfer Protein (LTP) Gene Expression to the Clubroot Disease and Salt Stress

The clubroot disease of Brassicaceae is caused by the obligate biotrophic protist Plasmodiophora brassicae. The disease is characterized by abnormal tumorous swellings of infected roots that result in reduced drought resistance and insufficient distribution of nutrients, leading to reduced crop yield. It is one of the most damaging diseases among cruciferous crops worldwide. The acquisition of nutrients by the protist is not well understood. Gene expression profiles in Arabidopsis thaliana clubroots indicate that lipid transfer proteins (LTPs) could be involved in disease development or at least in adaptation to the disease symptoms. Therefore, the aim of the study was to examine the role of some, of the still enigmatic LTPs during clubroot development. For a functional approach, we have generated transgenic plants that overexpress LTP genes in a root specific manner or show reduced LTP gene expression. Our results showed that overexpression of some of the LTP genes resulted in reduced disease severity whereas the lipid content in clubs of LTP mutants seems to be unaffected. Additional studies indicate a role for some LTPs during salt stress conditions in roots of A. thaliana.

Non-specific lipid transfer proteins in plants: presenting new advances and an integrated functional analysis

Plant non-specific lipid-transfer proteins (nsLTPs) are small, basic proteins present in abundance in higher plants. They are involved in key processes of plant cytology, such as the stablization of membranes, cell wall organization, and signal transduction. nsLTPs are also known to play important roles in resistance to biotic and abiotic stress, and in plant growth and development, such as sexual reproduction, seed development and germination. The structures of plant nsLTPs contain an eight-cysteine residue conserved motif, linked by four disulfide bonds, and an internal hydrophobic cavity, which comprises the lipid-binding site. This structure endows stability and increases the ability to bind and/or carry hydrophobic molecules. There is growing interest in nsLTPs, due to their critical roles, resulting in the need for a comprehensive review of their form and function. Relevant topics include: nsLTP structure and biochemical features, their classification, identification, and characterization across species, sub-cellular localization, lipid binding and transfer ability, expression profiling, functionality, and evolution. We present advances, as well as limitations and trends, relating to the different topics of the nsLTP gene family. This review collates a large body of research pertaining to the role of nsLTPs across the plant kingdom, which has been integrated as an in depth functional analysis of this group of proteins as a whole, and their activities across multiple biochemical pathways, based on a large number of reports. This review will enhance our understanding of nsLTP activity in planta, prompting further work and insights into the roles of this multifaceted protein family in plants.

A wheat lipid transfer protein 3 could enhance the basal thermotolerance and oxidative stress resistance of Arabidopsis

Wheat (Triticum aestivum L.) is one of the major grain crops, and heat stress adversely affects wheat production in many regions of the world. Previously, we found a heat-responsive gene named Lipid Transfer Protein 3 (TaLTP3) in wheat. TaLTP3 was deduced to be regulated by cold, ABA, MeJA, Auxin and oxidative stress according to cis-acting motifs in its promoter sequences. In this study, we show that TaLTP3 is responsive to prolonged water deficit, salt or ABA treatment in wheat seedlings. Also, TaLTP3 accumulation was observed after the plant suffered from heat stress both at the seedling and the grain-filling stages. TaLTP3 protein was localized in the cell membrane and cytoplasm of tobacco epidermal cells. Overexpression of TaLTP3 in yeast imparted tolerance to heat stress compared to cells expressing the vector alone. Most importantly, transgenic Arabidopsis plants engineered to overexpress TaLTP3 showed higher thermotolerance than control plants at the seedling stage. Further investigation indicated that transgenic lines decreased H₂O₂ accumulation and membrane injury under heat stress. Taken together, our results demonstrate that TaLTP3 confers heat stress tolerance possibly through reactive oxygen species (ROS) scavenging.

Intersection of population variation and autoimmunity genetics in human T cell activation

T lymphocyte activation by antigen conditions adaptive immune responses and immunopathologies, but we know little about its variation in humans and its genetic or environmental roots. We analyzed gene expression in CD4(+) T cells during unbiased activation or in T helper 17 (T(H)17) conditions from 348 healthy participants representing European, Asian, and African ancestries. We observed interindividual variability, most marked for cytokine transcripts, with clear biases on the basis of ancestry, and following patterns more complex than simple T(H)1/2/17 partitions. We identified 39 genetic loci specifically associated in cis with activated gene expression. We further fine-mapped and validated a single-base variant that modulates YY1 binding and the activity of an enhancer element controlling the autoimmune-associated IL2RA gene, affecting its activity in activated but not regulatory T cells. Thus, interindividual variability affects the fundamental immunologic process of T helper activation, with important connections to autoimmune disease.

Identification of wheat non-specific lipid transfer proteins involved in chilling tolerance

Three TaLTPs were found to enhance chilling tolerance of transgenic Arabidopsis, which were characterized by analyzes of promoter-GUS activity, subcellular localization, chromosomal location and transcriptional profile. Non-specific lipid transfer proteins (nsLTP) are abundantly expressed in plants, however, their functions are still unclear. In this study, we primarily characterized the functions of 3 type I TaLTP genes that were localized on chromosomes 3A, 3B, and 5D, respectively. The transcripts of TaLTPIb.1 and TaLTPIb.5 were induced under chilling, wound, and drought conditions, while TaLTPId.1 was only up-regulated by dark treatment. All the 3 TaLTP genes could be stimulated by the in vitro treatment of salicylic acid, while TaLTPId.1 was also positively regulated by methyljasmonic acid. Furthermore, the promoter-reporter assay of TaLTPIb.1 in the transgenic brachypodium showed a typical epidermis-specific expression pattern of this gene cluster. When fused with EGFP, all the 3 proteins were shown to localize on the plasma membrane in transgenic tobacco, although a signal in chloroplasts was also observed for TaLTPId.1. Heterogeneous overexpression of each of the TaLTP genes in Arabidopsis resulted in longer root length compared with wild type plants under chilling condition. These results suggest that type I TaLTPs may have a conserved functionality in chilling tolerance by lipid permeation in the plasma membrane of epidermal cells. On the other hand, the type I TaLTPs may exert functional divergence mainly through regulatory subfunctionalization.

Evolutionary history of trihelix family and their functional diversification

In this study, we carried out an evolutionary, transcriptional, and functional analyses of the trihelix transcription factor family. A total of 319 trihelix members, identified from 11 land plant species, were classified into five clades. The results of phylogeny indicate the binding domains of GT1 and GT2 diverged early in the existence of land plants. Genomic localization revealed that the trihelix family members were highly conserved among cereal species, even though some homeologs generated during the tetraploidy of maize were lost. Three-dimensional structural analyses and an examination of subcellular localization of this family supported the involvement of all five clades in transcriptional regulation. Furthermore, the family members from all clades in sorghum and rice showed a broad and dynamic expression pattern in response to abiotic stresses, indicating regulatory subfunctionalization of their original functions. This finding is further supported by the phenotypes of enhanced tolerance to cold, salt, and drought in transgenic plants overexpressing Sb06g023980 and Sb06g024110. In contrast, few Arobidopsis genes showed inducible expression under abiotic stress conditions, which may indicate a functional shift. Finally, our co-expression analysis points to the involvement of this family in various metabolic processes, implying their further functional divergence.

Structural genes of wheat and barley 5-methylcytosine DNA glycosylases and their potential applications for human health

Wheat supplies about 20% of the total food calories consumed worldwide and is a national staple in many countries. Besides being a key source of plant proteins, it is also a major cause of many diet-induced health issues, especially celiac disease. The only effective treatment for this disease is a total gluten-free diet. The present report describes an effort to develop a natural dietary therapy for this disorder by transcriptional suppression of wheat DEMETER (DME) homeologs using RNA interference. DME encodes a 5-methylcytosine DNA glycosylase responsible for transcriptional derepression of gliadins and low-molecular-weight glutenins (LMWgs) by active demethylation of their promoters in the wheat endosperm. Previous research has demonstrated these proteins to be the major source of immunogenic epitopes. In this research, barley and wheat DME genes were cloned and localized on the syntenous chromosomes. Nucleotide diversity among DME homeologs was studied and used for their virtual transcript profiling. Functional conservation of DME enzyme was confirmed by comparing the motif and domain structure within and across the plant kingdom. Presence and absence of CpG islands in prolamin gene sequences was studied as a hallmark of hypo- and hypermethylation, respectively. Finally the epigenetic influence of DME silencing on accumulation of LMWgs and gliadins was studied using 20 transformants expressing hairpin RNA in their endosperm. These transformants showed up to 85.6% suppression in DME transcript abundance and up to 76.4% reduction in the amount of immunogenic prolamins, demonstrating the possibility of developing wheat varieties compatible for the celiac patients.

Insight into the molecular evolution of non-specific lipid transfer proteins via comparative analysis between rice and sorghum

Phylogenetic analysis was conducted on 9 kDa non-specific lipid transfer protein (nsLTP) genes from nine plant species. Each of the five classified types in angiosperms exhibited eight conserved cysteine patterns. The most abundant nsLTP genes fell into the type I category, which was particularly enriched in a grass-specific lineage of clade I.1. Six pairs of tandem copies of nsLTP genes on the distal region of rice chromosomes 11 and 12 were well-preserved under concerted evolution, which was not observed in sorghum. The transgenic promoter–reporter assay revealed that both rice and sorghum nsLTP genes of type I displayed a relatively conserved expression feature in the epidermis of growing tissue, supporting its functional roles in cutin synthesis or defence against phytopathogens. For type I, the frequent expression in the stigma and seed are indicative of functional involvement in pistil–pollen interactions and seed development. By way of contrast, several type V genes were observed, mainly in the vascular bundle of the rosette as well as the young shoots, which might be related with vascular tissue differentiation or defence signalling. Compared with sorghum, the highly redundant tissue-specific expression pattern among members of rice nsLTP genes in clade I.1 suggests that concerted evolution via gene conversion favours the preservation of crucial expression motifs via the homogenization of proximal promoter sequences under high selection constraints. However, extensive regulatory subfunctionalization might also have occurred under relative low selection constraints, resulting in functional divergence at the expression level.

Comparative analysis of evolutionary dynamics of genes encoding leucine-rich repeat receptor-like kinase between rice and Arabidopsis

The leucine-rich repeat (LRR) receptor kinase (RLK) proteins constitute a large superfamily in the plant genome, and carry out key functions in a variety of biological pathways. In an effort to determine the evolutionary fate of members of a large gene family such as plant LRR RLK proteins we conducted in silico analysis using complete genome sequencing datasets, genome-wide transcriptome databases, and bioinformatics tools. A total of 292 and 165 LRR RLK genes were retrieved from the rice and Arabidopsis genomes, respectively, formed by diverse duplication events for gene expansion. The phylogenic analyses of the LRR RLK genes suggested combinations of LRR domains and RLK domains in the ancient plant genome prior to the divergence of rice and Arabidopsis, followed by massive independent expansions during speciation. The somewhat high frequencies (50-73%) of expressional divergence of members of duplicate gene pairs formed by whole/segmental genome duplication (W/SGD) and tandem duplication (TD) events of Arabidopsis and TD events of rice support the idea of their functional diversity for gene retention. By contrast, a relatively low degree (at least 20%) of members of rice LRR RLK gene pairs formed by W/SGD appear to be divergent in expression following the duplication event. At least 7 pairs of co-expressed gene clusters, including each of the tentative orthologous LRR RLK genes between rice and Arabidopsis, were enriched to an orthologous set between members of each of the pairs as compared to those of the random pairs, suggesting some degree of functional conservation of individual genes. These results may shed some light on the crucial functions of the plant LRR RLK genes with regard to a variety of biological processes.