Overexpression of tomato chloroplast-targeted DnaJ protein enhances tolerance to drought stress and resistance to Pseudomonas solanacearum in transgenic tobacco

Enhanced Desiccation Tolerance in Mature Cultures of the Streptophytic Green Alga Zygnema circumcarinatum Revealed by Transcriptomics

Desiccation tolerance is commonly regarded as one of the key features for the colonization of terrestrial habitats by green algae and the evolution of land plants. Extensive studies, focused mostly on physiology, have been carried out assessing the desiccation tolerance and resilience of the streptophytic genera Klebsormidium and Zygnema. Here we present transcriptomic analyses of Zygnema circumcarinatum exposed to desiccation stress. Cultures of Z. circumcarinatum grown in liquid medium or on agar plates were desiccated at ∼86% relative air humidity until the effective quantum yield of PSII [Y(II)] ceased. In general, the response to dehydration was much more pronounced in Z. circumcarinatum cultured in liquid medium for 1 month compared with filaments grown on agar plates for 7 and 12 months. Culture on solid medium enables the alga to acclimate to dehydration much better and an increase in desiccation tolerance was clearly correlated to increased culture age. Moreover, gene expression analysis revealed that photosynthesis was strongly repressed upon desiccation treatment in the liquid culture while only minor effects were detected in filaments cultured on agar plates for 7 months. Otherwise, both samples showed induction of stress protection mechanisms such as reactive oxygen species scavenging (early light-induced proteins, glutathione metabolism) and DNA repair as well as the expression of chaperones and aquaporins. Additionally, Z. circumcarinatum cultured in liquid medium upregulated sucrose-synthesizing enzymes and strongly induced membrane modifications in response to desiccation stress. These results corroborate the previously described hardening and associated desiccation tolerance in Zygnema in response to seasonal fluctuations in water availability.

Identification of Genes Involved in the Responses of Tangor (C. reticulata × C. sinensis) to Drought Stress

Drought is the major abiotic stress with adverse effects on citrus, decreasing the agronomical yield and influencing the fruit quality. In this study, cDNA-amplified fragment length polymorphism (cDNA-AFLP) technique was used to investigate the transcriptional profile changes and identify drought-responsive genes in “Amakusa” tangor (C. reticulata × C. sinensis), a hybrid citrus sensitive to water stress. The 255 out of 6,245 transcript-derived fragments (TDFs) displayed altered expression patterns including (A) induction, (B) repression, (C) upregulation, and (D) downregulation. With BLAST search, the gene products of differentially expressed fragments (DEFs) could be classified into several categories: cellular processes, transcription, transport, metabolism, stress/stimuli response, and developmental processes. Downregulated genes were highly represented by photosynthesis and basic metabolism, while upregulated ones were enriched in genes that were involved in transcription regulation, defense, energy, and transport. Present result also revealed some transient and up- and then downregulated genes such as aquaporin protein and photosystem enzyme. Expression patterns of 17 TDFs among 18 homologous to function-known genes were confirmed by qRT-PCR analysis. The present results revealed potential mechanism of drought tolerance in fruit crop and also provided candidate genes for future experiments in citrus.

RdreB1BI enhances drought tolerance by activating AQP-related genes in transgenic strawberry

The dehydration-responsive element binding protein (DREB) family of transcription factors is associated with abiotic stress responses during plant growth and development. This study focussed on the subfamily member DREB1B, which was initially described as highly and specifically responsive to low temperature. However, here it is shown that DREB1B is not only involved in cold tolerance but also other abiotic stress tolerances, such as that of drought. To further understand the genetic improvement effects of the drought tolerance provided by RdreB1BI in transgenic strawberry, drought stress responses of transgenic plants were evaluated at the morphological, physiological, and transcriptional levels. Transactivation assays revealed that RdreB1BI could activate the FvPIP2;1 like 1 promoter. RdreB1BI transgenic plants showed enhanced drought tolerance on the basis of lower rates of electrolyte leakage (EL), higher relative water content (RWC), and less stomatal aperture as well as increased peroxidase (POD) and superoxide dismutase (SOD) activities and less malondialdehyde (MDA) accumulation. The transgenic plants also accumulated higher levels of drought-related regulatory genes and functional gene transcripts, including those of PIP, NAC, RD22, ABI, and NCED. Together, these results demonstrate that RdreB1BI plays an essential role in the regulation of the drought stress response. DREB1B transcription constitutes a useful strategy to exploit in transgenic plants for coping with abiotic stresses, at least cold and drought stresses. The approach may be helpful for genetic engineering horticultural plants to have increased environmental adaptations.

SlCOR413IM1: A novel cold-regulation gene from tomato, enhances drought stress tolerance in tobacco

Drought stress adversely affects plant growth, development, and productivity. Genes functioning in plant response to drought stress are essential for drought tolerance. In this study, SlCOR413IM1, a cold-regulated gene isolated from Solanum lycopersium, was transferred to Nicotiana tabacum to investigate its function under drought stress. The subcellular localisation of SlCOR413IM1-GFP fusion protein in Arabidopsis protoplasts suggested that SlCOR413IM1 is a chloroplast protein. Expression analyses revealed that SlCOR413IM1 responded to drought and cold stresses. Under drought stress, transgenic plants maintained the high maximum photochemical efficiency, net photosynthetic rate (Pn) and D1 protein content of photosystem II (PSII). Compared with wild-type (WT) plants, transgenic plants showed higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities and proline and soluble sugar content, which reduced reactive oxygen species (ROS) generation. However, the high SOD and APX activities in transgenic plants were independent of their transcription levels. Moreover, the transgenic plants exhibited better seed germination, water status and survival, as well as lower malondialdehyde (MDA) content and relative electrical conductivity (REC) than WT plants under drought stress. Taken together, these data demonstrated that overexpression of SlCOR413IM1 enhanced drought stress tolerance in transgenic tobacco.

The DnaJ Gene Family in Pepper (Capsicum annuum L.): Comprehensive Identification, Characterization and Expression Profiles

The DnaJ proteins which function as molecular chaperone played critical roles in plant growth and development and response to heat stress (HS) and also called heat shock protein 40 based on molecular weight. However, little was reported on this gene family in pepper. Recently, the release of the whole pepper genome provided an opportunity for identifying putative DnaJ homologous. In this study, a total of 76 putative pepper DnaJ genes (CaDnaJ01 to CaDnaJ76) were identified using bioinformatics methods and classified into five groups by the presence of the complete three domains (J-domain, zinc finger domain, and C-terminal domain). Chromosome mapping suggested that segmental duplication and tandem duplication were occurred in evolution. The multiple stress-related cis-elements were found in the promoter region of these CaDnaJ genes, which indicated that the CaDnaJs might be involved in the process of responding to complex stress conditions. In addition, expression profiles based on RNA-seq showed that the 47 CaDnaJs were expressed in at least one tissue tested. The result implied that they could be involved in the process of pepper growth and development. qRT-PCR analysis found that 80.60% (54/67) CaDnaJs were induced by HS, indicated that they could participated in pepper response to high temperature treatments. In conclusion, all these results would provide a comprehensive basis for further analyzing the function of CaDnaJ members and be also significant for elucidating the evolutionary relationship in pepper.

Tomato SlGGP-LIKE gene participates in plant responses to chilling stress and pathogenic infection

Plants are always exposed to abiotic and biotic stresses which can adversely affect their growth and development. As an important antioxidant, AsA plays a vital role in plant defence against damage caused by stresses. In this study, we cloned a tomato GDP-_L-galactose phosphorylase-like (SlGGP-LIKE) gene and investigated its role in resistance to abiotic and biotic stresses by using antisense transgenic (AS) tomato lines. The AsA content in AS plants was lower than that in WT plants. Under chilling stress, the growth of AS plants was inhibited significantly, and they yielded higher levels of ROS, REC and MDA but demonstrated weaker APX activity than that shown by WT plants. Additionally, the declined values of Pn, Fv/Fm, oxidisable P700, and D1 protein content of PSII in AS lines were significant. Furthermore, the effect on xanthophyll cycle of AS plants was more severe than that on WT plants, and the ratio of zeaxanthin (Z)/(V + A + Z) and (Z + 0.5 A)/(V + A + Z) in AS lines was lower than that in WT plants. In spite of chilling stress, under Pseudomonas syringae pv.tomato (Pst) DC3000 strain infection, AS plants showed lesser bacterial cell growth and dead cells than those shown by WT plants. This finding indicated that AS plants demonstrated stronger resistance against pathogenic infection. Results suggest that SlGGP-LIKE gene played an important role in plant defence against chilling stress and pathogenic infection.

The ANGULATA7 gene encodes a DnaJ-like zinc finger-domain protein involved in chloroplast function and leaf development in Arabidopsis

The characterization of mutants with altered leaf shape and pigmentation has previously allowed the identification of nuclear genes that encode plastid-localized proteins that perform essential functions in leaf growth and development. A large-scale screen previously allowed us to isolate ethyl methanesulfonate-induced mutants with small rosettes and pale green leaves with prominent marginal teeth, which were assigned to a phenotypic class that we dubbed Angulata. The molecular characterization of the 12 genes assigned to this phenotypic class should help us to advance our understanding of the still poorly understood relationship between chloroplast biogenesis and leaf morphogenesis. In this article, we report the phenotypic and molecular characterization of the angulata7-1 (anu7-1) mutant of Arabidopsis thaliana, which we found to be a hypomorphic allele of the EMB2737 gene, which was previously known only for its embryonic-lethal mutations. ANU7 encodes a plant-specific protein that contains a domain similar to the central cysteine-rich domain of DnaJ proteins. The observed genetic interaction of anu7-1 with a loss-of-function allele of GENOMES UNCOUPLED1 suggests that the anu7-1 mutation triggers a retrograde signal that leads to changes in the expression of many genes that normally function in the chloroplasts. Many such genes are expressed at higher levels in anu7-1 rosettes, with a significant overrepresentation of those required for the expression of plastid genome genes. Like in other mutants with altered expression of plastid-encoded genes, we found that anu7-1 exhibits defects in the arrangement of thylakoidal membranes, which appear locally unappressed.

A novel tomato SUMO E3 ligase, SlSIZ1, confers drought tolerance in transgenic tobacco

SUMOylation is an important post-translational modification process that regulates different cellular functions in eukaryotes. SIZ/PIAS-type SAP and Miz1 (SIZ1) proteins exhibit SUMO E3 ligase activity, which modulates SUMOylation. However, SIZ1 in tomato has been rarely investigated. In this study, a tomato SIZ1 gene (SlSIZ1) was isolated and its molecular characteristics and role in tolerance to drought stress are described. SlSIZ1 was up-regulated by cold, sodium chloride (NaCl), polyethylene glycol (PEG), hydrogen peroxide (H2 O2 ) and abscisic acid (ABA), and the corresponding proteins were localized in the nucleus. The expression of SlSIZ1 in Arabidopsis thaliana (Arabidopsis) siz1-2 mutants partially complemented the phenotypes of dwarf, cold sensitivity and ABA hypersensitivity. SlSIZ1 also exhibited the activity of SUMO E3 ligase to promote the accumulation of SUMO conjugates. Under drought stress, the ectopic expression of SlSIZ1 in transgenic tobacco lines enhanced seed germination and reduced the accumulation of reactive oxygen species. SlSIZ1 overexpression conferred the plants with improved growth, high free proline content, minimal malondialdehyde accumulation and increased accumulation of SUMO conjugates. SlSIZ1 is a functional homolog of Arabidopsis SIZ1 with SUMO E3 ligase activity. Therefore, overexpression of SlSIZ1 enhanced the tolerance of transgenic tobacco to drought stress.

Comparative transcriptome profiling of chilling stress responsiveness in grafted watermelon seedlings

Rootstock grafting may improve the resistance of watermelon plants to low temperatures. However, information regarding the molecular responses of rootstock grafted plants to chilling stress is limited. To elucidate the molecular mechanisms of chilling tolerance in grafted plants, the transcriptomic responses of grafted watermelon under chilling stress were analyzed using RNA-seq analysis. Sequencing data were used for digital gene expression (DGE) analysis to characterize the transcriptomic responses in grafted watermelon seedlings. A total of 702 differentially-expressed genes (DEGs) were found in rootstock grafted (RG) watermelon relative to self-grafted (SG) watermelon; among these genes, 522 genes were up-regulated and 180 were down-regulated. Additionally, 164 and 953 genes were found to specifically expressed in RG and SG seedlings under chilling stress, respectively. Functional annotations revealed that up-regulated DEGs are involved in protein processing, plant-pathogen interaction and the spliceosome, whereas down-regulated DEGs are associated with photosynthesis. Moreover, 13 DEGs were randomly selected for quantitative real time PCR (qRT-PCR) analysis. The expression profiles of these 13 DEGs were consistent with those detected by the DGE analysis, supporting the reliability of the DGE data. This work provides additional insight into the molecular basis of grafted watermelon responses to chilling stress.

Association mapping reveals the genetic architecture of tomato response to water deficit: focus on major fruit quality traits

Water scarcity constitutes a crucial constraint for agriculture productivity. High-throughput approaches in model plant species identified hundreds of genes potentially involved in survival under drought, but few having beneficial effects on quality and yield. Nonetheless, controlled water deficit may improve fruit quality through higher concentration of flavor compounds. The underlying genetic determinants are still poorly known. In this study, we phenotyped 141 highly diverse small fruit tomato accessions for 27 traits under two contrasting watering conditions. A subset of 55 accessions exhibited increased metabolite contents and maintained yield under water deficit. Using 6100 single nucleotide polymorphisms (SNPs), association mapping revealed 31, 41, and 44 quantitative trait loci (QTLs) under drought, control, and both conditions, respectively. Twenty-five additional QTLs were interactive between conditions, emphasizing the interest in accounting for QTLs by watering regime interactions in fruit quality improvement. Combining our results with the loci previously identified in a biparental progeny resulted in 11 common QTLs and contributed to a first detailed characterization of the genetic determinants of response to water deficit in tomato. Major QTLs for fruit quality traits were dissected and candidate genes were proposed using expression and polymorphism data. The outcomes provide a basis for fruit quality improvement under deficit irrigation while limiting yield losses.

Soil Salt Distribution and Tomato Response to Saline Water Irrigation under Straw Mulching

To investigate better saline water irrigation scheme for tomatoes that scheduling with the compromise among yield (Y_t), quality, irrigation water use efficiency (IWUE) and soil salt residual, an experiment with three irrigation quotas and three salinities of irrigation water was conducted under straw mulching in northern China. The irrigation quota levels were 280 mm (W1), 320 mm (W2) and 360 mm (W3), and the salinity levels were 1.0 dS/m (F), 3.0 dS/m (S1) and 5.0 dS/m (S2). Compared to freshwater, saline water irrigations decreased the maximum leaf area index (LAI_m) of tomatoes, and the LAI_m presented a decline tendency with higher salinity and lower irrigation quota. The best overall quality of tomato was obtained by S2W1, with the comprehensive quality index of 3.61. A higher salinity and lower irrigation quota resulted in a decrease of individual fruit weight and an increase of the blossom-end rot incidence, finally led to a reduction in the tomato Y_t and marketable yield (Y_m). After one growth season of tomato, the mass fraction of soil salt in plough layer under S2W1 treatment was the highest, and which presented a decline trend with an increasing irrigation quota. Moreover, compared to W1, soil salts had a tendency to move to the deeper soil layer when using W2 and W3 irrigation quota. According to the calculation results of projection pursuit model, S1W3 was the optimal treatment that possessed the best comprehensive benefit (tomato overall quality, Y_t, Y_m, IWUE and soil salt residual), and was recommended as the saline water irrigation scheme for tomatoes in northern China.

Overexpression of a novel NAC-type tomato transcription factor, SlNAM1, enhances the chilling stress tolerance of transgenic tobacco

The NAC proteins are the largest transcription factors in plants. The functions of NACs are various and we focus on their roles in response to abiotic stress here. In our study, a typical NAC gene (SlNAM1) is isolated from tomato and its product is located in the nucleus. It also has a transcriptional activity region situated in C-terminal. The expression levels of SlNAM1 in tomato were induced by 4°C, PEG, NaCl, abscisic acid (ABA) and methyl jasmonate (MeJA) treatments. The function of SlNAM1 in response to chilling stress has been investigated. SlNAM1 overexpression in tobacco exhibited higher germination rates, minor wilting, and higher photosynthetic rates (Pn) under chilling stress. Meanwhile, overexpression of SlNAM1 improved the osmolytes contents and reduced the H2O2 and O2•- contents under low temperature, which contribute to alleviating the oxidative damage of cell membrane after chilling stress. Moreover, the transcripts of NtDREB1, NtP5CS, and NtERD10s were higher in transgenic tobacco, and those increased expressions may confer higher chilling tolerance of transgenic plants. These results indicated that overexpression of SlNAM1 could improve chilling stress tolerance of transgenic tobacco.

Orange protein has a role in phytoene synthase stabilization in sweetpotato

Carotenoids have essential roles in light-harvesting processes and protecting the photosynthetic machinery from photo-oxidative damage. Phytoene synthase (PSY) and Orange (Or) are key plant proteins for carotenoid biosynthesis and accumulation. We previously isolated the sweetpotato (Ipomoea batatas) Or gene (IbOr), which is involved in carotenoid accumulation and salt stress tolerance. The molecular mechanism underlying IbOr regulation of carotenoid accumulation was unknown. Here, we show that IbOr has an essential role in regulating IbPSY stability via its holdase chaperone activity both in vitro and in vivo. This protection results in carotenoid accumulation and abiotic stress tolerance. IbOr transcript levels increase in sweetpotato stem, root, and calli after exposure to heat stress. IbOr is localized in the nucleus and chloroplasts, but interacts with IbPSY only in chloroplasts. After exposure to heat stress, IbOr predominantly localizes in chloroplasts. IbOr overexpression in transgenic sweetpotato and Arabidopsis conferred enhanced tolerance to heat and oxidative stress. These results indicate that IbOr holdase chaperone activity protects IbPSY stability, which leads to carotenoid accumulation, and confers enhanced heat and oxidative stress tolerance in plants. This study provides evidence that IbOr functions as a molecular chaperone, and suggests a novel mechanism regulating carotenoid accumulation and stress tolerance in plants.

A stress-associated NAC transcription factor (SlNAC35) from tomato plays a positive role in biotic and abiotic stresses

The NAC transcription factor family participates in responses to various kinds of environmental stimuli in plants. Responses of NAC genes to abiotic stresses have been widely studied, but their functions in response to biotic stress are little reported in plants, especially in crops. In the present study, we examined the functions of a novel tomato (Solanum lycopersicum) NAC protein (SlNAC35) in abiotic and biotic stress resistance by using transgenic tobacco. Expression analysis found that SlNAC35 expression was induced by drought stress, salt stress, bacterial pathogen, and signaling molecules, suggesting its involvement in plant responses to biotic and abiotic stimuli. Moreover, transgenic lines exhibited a greater number of lateral roots and longer root length compared with Vec lines (empty vector lines) after drought and salt treatment. These results indicate that overexpression of SlNAC35 promoted root growth and development under drought and salt stresses. Higher expressions of NtARF1, NtARF2 and NtARF8 were observed under drought and salt stresses in transgenic lines, suggesting that overexpression of SlNAC35 promoted growth and development of roots in transgenic lines possibly by involving auxin signaling and by regulating NtARF expression. In addition, SlNAC35 overexpression improved resistance to bacterial pathogen in transgenic tobacco, and reactive oxygen species may be in the upstream of salicylic acid (SA) signaling in transgenic tobacco during defense response.

Gel-Free/Label-Free Proteomic Analysis of Endoplasmic Reticulum Proteins in Soybean Root Tips under Flooding and Drought Stresses

Soybean is a widely cultivated crop; however, it is sensitive to flooding and drought stresses. The adverse environmental cues cause the endoplasmic reticulum (ER) stress due to accumulation of unfolded or misfolded proteins. To investigate the mechanisms in response to flooding and drought stresses, ER proteomics was performed in soybean root tips. The enzyme activity of NADH cytochrome c reductase was two-fold higher in the ER than other fractions, indicating that the ER was isolated with high purity. Protein abundance of ribosomal proteins was decreased under both stresses compared to control condition; however, the percentage of increased ribosomes was two-fold higher in flooding compared to drought. The ER proteins related to protein glycosylation and signaling were in response to both stresses. Compared to control condition, calnexin was decreased under both stresses; however, protein disulfide isomerase-like proteins and heat shock proteins were markedly decreased under flooding and drought conditions, respectively. Furthermore, fewer glycoproteins and higher levels of cytosolic calcium were identified under both stresses compared to control condition. These results suggest that reduced accumulation of glycoproteins in response to both stresses might be due to dysfunction of protein folding through calnexin/calreticulin cycle. Additionally, the increased cytosolic calcium levels induced by flooding and drought stresses might disturb the ER environment for proper protein folding in soybean root tips.

Comparative shotgun proteomic analysis of wild and domesticated Opuntia spp. species shows a metabolic adaptation through domestication

The Opuntia genus is widely distributed in America, but the highest richness of wild species are found in Mexico, as well as the most domesticated Opuntia ficus-indica, which is the most domesticated species and an important crop in agricultural economies of arid and semiarid areas worldwide. During domestication process, the Opuntia morphological characteristics were favored, such as less and smaller spines in cladodes and less seeds in fruits, but changes at molecular level are almost unknown. To obtain more insights about the Opuntia molecular changes through domestication, a shotgun proteomic analysis and database-dependent searches by homology was carried out. >1000 protein species were identified and by using a label-free quantitation method, the Opuntia proteomes were compared in order to identify differentially accumulated proteins among wild and domesticated species. Most of the changes were observed in glucose, secondary, and 1C metabolism, which correlate with the observed protein, fiber and phenolic compounds accumulation in Opuntia cladodes. Regulatory proteins, ribosomal proteins, and proteins related with response to stress were also observed in differential accumulation. These results provide new valuable data that will help to the understanding of the molecular changes of Opuntia species through domestication.

BIOLOGICAL SIGNIFICANCE

Opuntia species are well adapted to dry and warm conditions in arid and semiarid regions worldwide, and they are highly productive plants showing considerable promises as an alternative food source. However, there is a gap regarding Opuntia molecular mechanisms that enable them to grow in extreme environmental conditions and how the domestication processes has changed them. In the present study, a shotgun analysis was carried out to characterize the proteomes of five Opuntia species selected by its domestication degree. Our results will help to a better understanding of proteomic features underlying the selection and specialization under evolution and domestication of Opuntia and will provide a platform for basic biology research and gene discovery.

The NF-YA transcription factor OsNF-YA7 confers drought stress tolerance of rice in an abscisic acid independent manner

The mechanisms of plant response and adaptation to drought stress require the regulation of transcriptional networks via the induction of drought-responsive transcription factors. Nuclear Factor Y (NF-Y) transcription factors have aroused interest in roles of plant drought stress responses. However, the molecular mechanism of the NF-Y-induced drought tolerance is not well understood. Here, we functionally analyzed two rice NF-YA genes, OsNF-YA7 and OsNF-YA4. Expression of OsNF-YA7 was induced by drought stress and its overexpression in transgenic rice plants improved their drought tolerance. In contrast, OsNF-YA4 expression was not increased by drought stress and its overexpression in transgenic rice plants did not affect their sensitivity to drought stress. OsNF-YA4 expression was highly induced by the stress-related hormone abscisic acid (ABA), while OsNF-YA7 was not, indicating that OsNF-YA7 mediates drought tolerance in an ABA-independent manner. Analysis of the OsNF-YA7 promoter revealed three ABA-independent DRE/CTR elements and RNA-seq analysis identified 48 genes downstream of OsNFYA7 action putatively involved in the OsNF-YA7-mediated drought tolerance pathway. Taken together, our results suggest an important role for OsNF-YA7 in rice drought stress tolerance.

Transcriptome-Wide Identification of Reference Genes for Expression Analysis of Soybean Responses to Drought Stress along the Day

The soybean transcriptome displays strong variation along the day in optimal growth conditions and also in response to adverse circumstances, like drought stress. However, no study conducted to date has presented suitable reference genes, with stable expression along the day, for relative gene expression quantification in combined studies on drought stress and diurnal oscillations. Recently, water deficit responses have been associated with circadian clock oscillations at the transcription level, revealing the existence of hitherto unknown processes and increasing the demand for studies on plant responses to drought stress and its oscillation during the day. We performed data mining from a transcriptome-wide background using microarrays and RNA-seq databases to select an unpublished set of candidate reference genes, specifically chosen for the normalization of gene expression in studies on soybean under both drought stress and diurnal oscillations. Experimental validation and stability analysis in soybean plants submitted to drought stress and sampled during a 24 h timecourse showed that four of these newer reference genes (FYVE, NUDIX, Golgin-84 and CYST) indeed exhibited greater expression stability than the conventionally used housekeeping genes (ELF1-β and β-actin) under these conditions. We also demonstrated the effect of using reference candidate genes with different stability values to normalize the relative expression data from a drought-inducible soybean gene (DREB5) evaluated in different periods of the day.

The DnaJ OsDjA7/8 is essential for chloroplast development in rice (Oryza sativa)

DnaJ proteins belong to chaperones of Hsp40 family that ubiquitously participate in various cellular processes. Previous studies have shown chloroplast-targeted DnaJs are involved in the development of chloroplast in some plant species. However, little is known about the function of DnaJs in rice, one of the main staple crops. In this study, we characterized a type I DnaJ protein OsDjA7/8. We found that the gene OsDjA7/8 was expressed in all collected tissues, with a priority in the vigorous growth leaf. Subcellular localization revealed that the protein OsDjA7/8 was mainly distributed in chloroplast. Reduced expression of OsDjA7/8 in rice led to albino lethal at the seedling stage. Transmission electron microscopy observation showed that the chloroplast structures were abnormally developed in the plants silenced for OsDjA7/8. In addition, the transcriptional expression of the genes tightly associated with the development of chloroplast was deeply reduced in the plants silenced for OsDjA7/8. Collectively, our study reveals that OsDjA7/8 encodes a chloroplast-localized protein and is essential for chloroplast development and differentiation in rice.

A tomato chloroplast-targeted DnaJ protein protects Rubisco activity under heat stress

Photosynthesis is one of the biological processes most sensitive to heat stress in plants. Carbon assimilation, which depends on ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), is one of the major sites sensitive to heat stress in photosynthesis. In this study, the roles of a tomato (Solanum lycopersicum) chloroplast-targeted DnaJ protein (SlCDJ2) in resisting heat using sense and antisense transgenic tomatoes were examined. SlCDJ2 was found to be uniformly distributed in the thylakoids and stroma of the chloroplasts. Under heat stress, sense plants exhibited higher chlorophyll contents and fresh weights, and lower accumulation of reactive oxygen species (ROS) and membrane damage. Moreover, Rubisco activity, Rubisco large subunit (RbcL) content, and CO2 assimilation capacity were all higher in sense plants and lower in antisense plants compared with wild-type plants. Thus, SlCDJ2 contributes to maintenance of CO2 assimilation capacity mainly by protecting Rubisco activity under heat stress. SlCDJ2 probably achieves this by keeping the levels of proteolytic enzymes low, which prevents accelerated degradation of Rubisco under heat stress. Furthermore, a chloroplast heat-shock protein 70 was identified as a binding partner of SlCDJ2 in yeast two-hybrid assays. Taken together, these findings establish a role for SlCDJ2 in maintaining Rubisco activity in plants under heat stress.

Overexpression of a tobacco J-domain protein enhances drought tolerance in transgenic Arabidopsis

DnaJ proteins constitute a DnaJ/Hsp40 family and are important regulators involved in diverse cellular functions. To date, the molecular mechanisms of DnaJ proteins involved in response to drought stress in plants are largely unknown. In this study, a putative DnaJ ortholog from Nicotiana tabacum (NtDnaJ1), which encodes a putative type-I J-protein, was isolated. The transcript levels of NtDnaJ1 were higher in aerial tissues and were markedly up-regulated by drought stress. Over-expression of NtDnaJ1 in Arabidopsis plants enhanced their tolerance to osmotic or drought stress. Quantitative determination of H2O2 accumulation has shown that H2O2 content increased in wild-type and transgenic seedlings under osmotic stress, but was significantly lower in both transgenic lines compared with the wild-type. Expression analysis of stress-responsive genes in NtDnaJ1-transgenic Arabidopsis revealed that there was significantly increased expression of genes involved in the ABA-dependent signaling pathway (AtRD20, AtRD22 and AtAREB2) and antioxidant genes (AtSOD1, AtSOD2, and AtCAT1). Collectively, these data demonstrate that NtDnaJ1 could be involved in drought stress response and its over-expression enhances drought tolerance possibly through regulating expression of stress-responsive genes. This study may facilitate our understandings of the biological roles of DnaJ protein-mediated abiotic stress in higher plants and accelerate genetic improvement of crop plants tolerant to environmental stresses.