Group 1 and 2 LEA protein expression correlates with a decrease in water stress induced protein aggregation in horsegram during germination and seedling growth

Adaptative Mechanisms of Halophytic Eutrema salsugineum Encountering Saline Environment

Salt cress (Eutrema salsugineum), an Arabidopsis-related halophyte, can naturally adapt to various harsh climates and soil conditions; thus, it is considered a desirable model plant for deciphering mechanisms of salt and other abiotic stresses. Accumulating evidence has revealed that compared with Arabidopsis, salt cress possesses stomata that close more tightly and more succulent leaves during extreme salt stress, a noticeably higher level of proline, inositols, sugars, and organic acids, as well as stress-associated transcripts in unstressed plants, and they are induced rapidly under stress. In this review, we systematically summarize the research on the morphology, physiology, genome, gene expression and regulation, and protein and metabolite profile of salt cress under salt stress. We emphasize the latest advances in research on the genome adaptive evolution encountering saline environments, and epigenetic regulation, and discuss the mechanisms underlying salt tolerance in salt cress. Finally, we discuss the existing questions and opportunities for future research in halophytic Eutrema. Together, the review fosters a better understanding of the mechanism of plant salt tolerance and provides a reference for the research and utilization of Eutrema as a model extremophile in the future. Furthermore, the prospects for salt cress applied to explore the mechanism of salt tolerance provide a theoretical basis to develop new strategies for agricultural biotechnology.

TMT-based comparative proteomic analysis of the male-sterile mutant ms01 sheds light on sporopollenin production and pollen development in wucai (Brassica campestris L.)

A spontaneous male-sterile mutant ms01 was discovered from the excellent high-generation inbred line 'hx12-6-3' in wucai. Compared with wild-type 'hx12-6-3', ms01 displayed complete male sterility with degenerated stamens and no pollen. In this study, cytological observation revealed that the tapetum of the anthers of ms01 had degraded in advance, and microspore development had stagnated in the mononuclear stage, ultimately resulting in completely aborted pollen. Genetic analysis indicated that the sterility of ms01 was controlled by a single recessive nuclear gene. In the differential proteomic analysis of 'hx12-6-3' and ms01 flower buds using a tandem mass tags-based approach, a comparison of two stages (stage a and stage e) revealed 1272 differentially abundant proteins (DAPs). The abnormal variation of the anther cuticle, pollen coat, and sporopollenin production were effected by lipid metabolism and phenylpropanoid biosynthesis in the mutant ms01. Further analysis elucidated that pollen development was associated with amino acid metabolism, protein synthesis and degradation, carbohydrate metabolism, flavonoid biosynthesis and glutathione metabolism. These results provide novel insights into the molecular mechanism of GMS (genic male sterility) in wucai. SIGNIFICANCE: ms01, as the first indentified spontaneous male-sterile mutant in wucai, plays a significant role in the initial study of GMS (genic male sterility). In our study, the key DAPs related to anther and pollen development were obtained by TMT-based comparative proteomic analysis. We found that the abnormal accumulation of H₂O₂ might induce premature degradation of the tapetum, causing anther metabolism disorder and pollen abortion. This process involved multiple DAPs and formed a complex regulatory network that generated a series of physiological metabolic alterations, ultimately leading to male sterility. Our results provide a theoretical foundation for further research on the complex anther and pollen development process.

Transcriptome Profiling of the Salt Stress Response in the Leaves and Roots of Halophytic Eutrema salsugineum

Eutrema salsugineum can grow in natural harsh environments; however, the underlying mechanisms for salt tolerance of Eutrema need to be further understood. Herein, the transcriptome profiling of Eutrema leaves and roots exposed to 300 mM NaCl is investigated, and the result emphasized the role of genes involved in lignin biosynthesis, autophagy, peroxisome, and sugar metabolism upon salt stress. Furthermore, the expression of the lignin biosynthesis and autophagy-related genes, as well as 16 random selected genes, was validated by qRT-PCR. Notably, the transcript abundance of a large number of lignin biosynthesis genes such as CCoAOMT, C4H, CCR, CAD, POD, and C3′H in leaves was markedly elevated by salt shock. And the examined lignin content in leaves and roots demonstrated salt stress led to lignin accumulation, which indicated the enhanced lignin level could be an important mechanism for Eutrema responding to salt stress. Additionally, the differentially expressed genes (DEGs) assigned in the autophagy pathway including Vac8, Atg8, and Atg4, as well as DEGs enriched in the peroxisome pathway such as EsPEX7, EsCAT, and EsSOD2, were markedly induced in leaves and/or roots. In sugar metabolism pathways, the transcript levels of most DEGs associated with the synthesis of sucrose, trehalose, raffinose, and xylose were significantly enhanced. Furthermore, the expression of various stress-related transcription factor genes including WRKY, AP2/ERF-ERF, NAC, bZIP, MYB, C2H2, and HSF was strikingly improved. Collectively, the increased expression of biosynthesis genes of lignin and soluble sugars, as well as the genes in the autophagy and peroxisome pathways, suggested that Eutrema encountering salt shock possibly possess a higher capacity to adjust osmotically and facilitate water transport and scavenge reactive oxidative species and oxidative proteins to cope with the salt environment. Thus, this study provides a new insight for exploring the salt tolerance mechanism of halophytic Eutrema and discovering new gene targets for the genetic improvement of crops.

Overexpression of rice OsLEA5 relieves the deterioration in seed quality caused by high-temperature stress

Late embryogenesis abundant protein (LEA) genes are widely conserved in seed plant species and form a multigene family. While some LEAs are known to respond to environmental stresses, the function of many LEAs is unknown. OsLEA5 (Lea14A) interacts with a regulator of the endosperm storage production, FLO2, suggesting that OsLEA5 may be involved in endosperm quality control. RNAi knockdown line of OsLEA5 showed decreased seed weight. Transformant lines overexpressing OsLEA5 exhibited improved quality and seed weight of mature seeds when they were developed under high-temperature conditions, while seed quality strongly declined in wild-type plants exposed to high-temperature stress. These findings indicate that OsLEA5 contributes to suppressing the deterioration of seed quality when developed under high-temperature conditions.

Modulation of photosynthesis and other proteins during water-stress

Protein changes under drought or water stress conditions have been widely investigated. These investigations have given us enormous understanding of how drought is manifested in plants and how plants respond and adopt to such conditions. Chlorophyll fluoroescence, gas exchange, OMICS, biochemical and molecular analyses have shed light on regulation of physiology and photosynthesis of plants under drought. Use of proteomics has greatly increased the repertoire of drought-associated proteins which nevertheless, need to be investigated for their mechanistic and functional roles. Roles of such proteins have been succinctly discussed in various review articles, however more information on their functional role in countering drought is needed. In this review, recent developments in the field, alterations in the abundance of plant proteins in response to drought, monitored through numerous proteomic and immuno-blot analyses, and how these could affect plants growth and development, are discussed.

A Novel Protein from Ectocarpus sp. Improves Salinity and High Temperature Stress Tolerance in Arabidopsis thaliana

Brown alga Ectocarpus sp. belongs to Phaeophyceae, a class of macroalgae that evolved complex multicellularity. Ectocarpus sp. is a dominant seaweed in temperate regions, abundant mostly in the intertidal zones, an environment with high levels of abiotic stresses. Previous transcriptomic analysis of Ectocarpus sp. revealed several genes consistently induced by various abiotic stresses; one of these genes is Esi0017_0056, which encodes a protein with unknown function. Bioinformatics analyses indicated that the protein encoded by Esi0017_0056 is soluble and monomeric. The protein was successfully expressed in Escherichia coli,Arabidopsis thaliana and Nicotiana benthamiana. In A. thaliana the gene was expressed under constitutive and stress inducible promoters which led to improved tolerance to high salinity and temperature stresses. The expression of several key abiotic stress-related genes was studied in transgenic and wild type A. thaliana by qPCR. Expression analysis revealed that genes involved in ABA-induced abiotic stress tolerance, K+ homeostasis, and chaperon activities were significantly up-regulated in the transgenic line. This study is the first report in which an unknown function Ectocarpus sp. gene, highly responsive to abiotic stresses, was successfully expressed in A. thaliana, leading to improved tolerance to salt and temperature stress.

Genetic Mapping Combined with a Transcriptome Analysis to Screen for Candidate Genes Responsive to Abscisic Acid Treatment in Brassica napus Embryos During Seed Germination

Brassica napus embryos contain precursor tissues for the leaves, stem, and root, as well as the cotyledons, and these precursor tissues play key roles in seed germination, seedling survival, and subsequent seedling growth. Abscisic acid (ABA) plays a prominent role in the inhibition of seed germination. The underlying molecular mechanisms of the embryo responses to ABA stress followed by inhibited seed germination have not been reported in B. napus to date. In this study, we conducted quantitative trait locus (QTL) analysis of B. napus seed in response to ABA stress using 170 recombinant inbred lines. Furthermore, we performed transcriptome sequencing (RNA-seq) analyses by using B. napus ZS11 embryos under sterile deionized water (control) and 10 mg/L (10A), 20 mg/L (20A), and 30 mg/L (30A) ABA treatment conditions. In total, 10 QTLs were screened for explaining 2.70-6.73% of the phenotypic variation under ABA stress. In addition, 1495, 3332, and 3868 differentially expressed genes (DEGs) were identified in the "control vs 10A," "control vs 20A," and "control vs 30A" comparisons, respectively. Gene Ontology (GO) enrichment analysis indicated that DEG functions are mainly related to response to stimuli, response to oxygen-containing compounds, response to lipids, and the transport and seed dormancy processes. These DEGs mainly participated in the response to plant hormone signal transduction, starch and sucrose metabolism, cutin, suberine, and wax biosynthesis, and phenylpropanoid biosynthesis processes pathways. Our results provide a foundation for further explorations of the molecular regulatory mechanisms of B. napus embryos in response to abiotic stress during the seed germination stage.

Global insights into high temperature and drought stress regulated genes by RNA-Seq in economically important oilseed crop Brassica juncea

BACKGROUND

Brassica juncea var. Varuna is an economically important oilseed crop of family Brassicaceae which is vulnerable to abiotic stresses at specific stages in its life cycle. Till date no attempts have been made to elucidate genome-wide changes in its transcriptome against high temperature or drought stress. To gain global insights into genes, transcription factors and kinases regulated by these stresses and to explore information on coding transcripts that are associated with traits of agronomic importance, we utilized a combinatorial approach of next generation sequencing and de-novo assembly to discover B. juncea transcriptome associated with high temperature and drought stresses.

RESULTS

We constructed and sequenced three transcriptome libraries namely Brassica control (BC), Brassica high temperature stress (BHS) and Brassica drought stress (BDS). More than 180 million purity filtered reads were generated which were processed through quality parameters and high quality reads were assembled de-novo using SOAPdenovo assembler. A total of 77750 unique transcripts were identified out of which 69,245 (89%) were annotated with high confidence. We established a subset of 19110 transcripts, which were differentially regulated by either high temperature and/or drought stress. Furthermore, 886 and 2834 transcripts that code for transcription factors and kinases, respectively, were also identified. Many of these were responsive to high temperature, drought or both stresses. Maximum number of up-regulated transcription factors in high temperature and drought stress belonged to heat shock factors (HSFs) and dehydration responsive element-binding (DREB) families, respectively. We also identified 239 metabolic pathways, which were perturbed during high temperature and drought treatments. Analysis of gene ontologies associated with differentially regulated genes forecasted their involvement in diverse biological processes.

CONCLUSIONS

Our study provides first comprehensive discovery of B. juncea transcriptome under high temperature and drought stress conditions. Transcriptome resource generated in this study will enhance our understanding on the molecular mechanisms involved in defining the response of B. juncea against two important abiotic stresses. Furthermore this information would benefit designing of efficient crop improvement strategies for tolerance against conditions of high temperature regimes and water scarcity.

Overexpression of Late Embryogenesis Abundant 14 enhances Arabidopsis salt stress tolerance

Late embryogenesis abundant (LEA) proteins are implicated in various abiotic stresses in higher plants. In this study, we identified a LEA protein from Arabidopsis thaliana, AtLEA14, which was ubiquitously expressed in different tissues and remarkably induced with increased duration of salt treatment. Subcellular distribution analysis demonstrated that AtLEA14 was mainly localized in the cytoplasm. Transgenic Arabidopsis and yeast overexpressing AtLEA14 all exhibited enhanced tolerance to high salinity. The transcripts of salt stress-responsive marker genes (COR15a, KIN1, RD29B and ERD10) were overactivated in AtLEA14 overexpressing lines compared with those in wild type plants under normal or salt stress conditions. In vivo and in vitro analysis showed that AtLEA14 could effectively stabilize AtPP2-B11, an important E3 ligase. These results suggested that AtLEA14 had important protective functions under salt stress conditions in Arabidopsis.

Understanding the cellular mechanism of recovery from freeze-thaw injury in spinach: possible role of aquaporins, heat shock proteins, dehydrin and antioxidant system

Recovery from reversible freeze-thaw injury in plants is a critical component of ultimate frost survival. However, little is known about this aspect at the cellular level. To explore possible cellular mechanism(s) for post-thaw recovery (REC), we used Spinacia oleracea L. cv. Bloomsdale leaves to first determine the reversible freeze-thaw injury point. Freeze (-4.5°C)-thaw-injured tissues (32% injury vs <3% in unfrozen control) fully recovered during post-thaw, as assessed by an ion leakage-based method. Our data indicate that photosystem II efficiency (Fv/Fm) was compromised in injured tissues but recovered during post-thaw. Similarly, the reactive oxygen species (O2 (•-) and H2 O2 ) accumulated in injured tissues but dissipated during recovery, paralleled by the repression and restoration, respectively, of activities of antioxidant enzymes, superoxide dismutase (SOD) (EC. 1.14.1.1), and catalase (CAT) (EC.1.11.1.6) and ascorbate peroxidase (APX) (EC.1.11.1.11). Restoration of CAT and APX activities during recovery was slower than SOD, concomitant with a slower depletion of H2 O2 compared to O2 (•-) . A hypothesis was also tested that the REC is accompanied by changes in the expression of water channels [aquaporines (AQPs)] likely needed for re-absorption of thawed extracellular water. Indeed, the expression of two spinach AQPs, SoPIP2;1 and SoδTIP, was downregulated in injured tissues and restored during recovery. Additionally, a notion that molecular chaperones [heat shock protein of 70 kDa (HSP70s)] and putative membrane stabilizers [dehydrins (DHNs)] are recruited during recovery to restore cellular homeostasis was also tested. We noted that, after an initial repression in injured tissues, the expression of three HSP70s (cytosolic, endoplasmic reticulum and mitochondrial) and a spinach DHN (CAP85) was significantly restored during the REC.

The physiology and proteomics of drought tolerance in maize: early stomatal closure as a cause of lower tolerance to short-term dehydration?

Understanding the response of a crop to drought is the first step in the breeding of tolerant genotypes. In our study, two maize (Zea mays L.) genotypes with contrasting sensitivity to dehydration were subjected to moderate drought conditions. The subsequent analysis of their physiological parameters revealed a decreased stomatal conductance accompanied by a slighter decrease in the relative water content in the sensitive genotype. In contrast, the tolerant genotype maintained open stomata and active photosynthesis, even under dehydration conditions. Drought-induced changes in the leaf proteome were analyzed by two independent approaches, 2D gel electrophoresis and iTRAQ analysis, which provided compatible but only partially overlapping results. Drought caused the up-regulation of protective and stress-related proteins (mainly chaperones and dehydrins) in both genotypes. The differences in the levels of various detoxification proteins corresponded well with the observed changes in the activities of antioxidant enzymes. The number and levels of up-regulated protective proteins were generally lower in the sensitive genotype, implying a reduced level of proteosynthesis, which was also indicated by specific changes in the components of the translation machinery. Based on these results, we propose that the hypersensitive early stomatal closure in the sensitive genotype leads to the inhibition of photosynthesis and, subsequently, to a less efficient synthesis of the protective/detoxification proteins that are associated with drought tolerance.

Overexpression of dehydrin tas14 gene improves the osmotic stress imposed by drought and salinity in tomato

One strategy to increase the level of drought and salinity tolerance is the transfer of genes codifying different types of proteins functionally related to macromolecules protection, such as group 2 of late embryogenesis abundant (LEA) proteins or dehydrins. The TAS14 dehydrin was isolated and characterized in tomato and its expression was induced by osmotic stress (NaCl and mannitol) and abscisic acid (ABA) [Godoy et al., Plant Mol Biol 1994;26:1921-1934], yet its function in drought and salinity tolerance of tomato remains elusive. In this study, transgenic tomato plants overexpressing tas14 gene under the control of the 35SCaMV promoter were generated to assess the function of tas14 gene in drought and salinity tolerance. The plants overexpressing tas14 gene achieved improved long-term drought and salinity tolerance without affecting plant growth under non-stress conditions. A mechanism of osmotic stress tolerance via osmotic potential reduction and solutes accumulation, such as sugars and K(+) is operating in tas14 overexpressing plants in drought conditions. A similar mechanism of osmotic stress tolerance was observed under salinity. Moreover, the overexpression of tas14 gene increased Na(+) accumulation only in adult leaves, whereas in young leaves, the accumulated solutes were K(+) and sugars, suggesting that plants overexpressing tas14 gene are able to distribute the Na(+) accumulation between young and adult leaves over a prolonged period in stressful conditions. Measurement of ABA showed that the action mechanism of tas14 gene is associated with an earlier and greater accumulation of ABA in leaves during short-term periods. A good feature for the application of this gene in improving drought and salt stress tolerance is the fact that its constitutive expression does not affect plant growth under non-stress conditions, and tolerance induced by overexpression of tas14 gene was observed at the different stress degrees applied to the long term.