Podosphaera xanthii Causing Powdery Mildew on Salvia farinacea in Central China.

Salvia farinacea, commonly referred as mealycup sage, is a perennial herbaceous plant belonging to the Salvia genus of the Lamiaceae family. It originates from the Mediterranean region, North America, and Europe and is globally cultivated due to its appealing and captivating flowers. Moreover, mealycup sage is utilized as traditional Chinese medicinal plant for treatment of cardiovascular diseases (Li et al. 2018). In October 2023, powdery mildew-like symptoms were observed on Salvia farinacea plants cultivated in a garden located in Xinxiang City, Henan Province, China (113.93, 35.29). The leaves were covered with white and thin masses of mycelia, conidiophores and conidia of the fungus. About 100 plants were checked and 90 % were infected. There were a large number of white colonies with irregular or continuous round lesions on the adaxial and abaxial surfaces of the leaves, covering approximately 80% of the leaf area. The slightly or straight curved conidiophores (n = 30) were 46 to 145× 8 to 11 µm in size and consisted of foot cells, shorter cells and conidia. The ellipsoidal to oval conidia (n = 30), containing fibrosin bodies, were 24 to 35 × 12 to 19 µm in size and had a length/width ratio of 1.8 to 2.1. No chasmothecia were observed on leaves. These morphological features were consistent with those of Podosphaera xanthii (Braun and Cook 2012). Following the previously described method (White et al. 1990; Bradshaw et al. 2022; Zhu et al. 2022a), the sequences of ITS and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) regions were amplified with specific primers ITS1/ITS4 (ITS1 5'-TCCGTAGGTGAACCTGCGG-3' ; ITS4 5'-TCCTCCGCTTATTGATATGC-3') and PMGAPDH1/PMGAPDH3R (PMGAPDH1 5'-GGAATGGCTATGCGTGTACC-3'; PMGAPDH3R 5'-CCCCATTCGTTGTCGTACCATG-3'), and the resulting sequences were uploaded in GenBank (Accession No. OR761885 and PP236082, respectively). BLASTn analysis showed that the sequence shared 560/565 (99%) and 272/272 (100%) homology with P. xanthii (MW301281) on Impatiens balsamina (Zhu et al. 2022b) and with P. xanthii (ON075658) on Cucumis melo (Bradshaw et al. 2022), respectively. The phylogenetic analysis clearly illustrated that the collected isolate of P. xanthii clustered in the same clade. The pathogenicity was tested according to the method previously described (Zhu et al. 2021). The fungus was inoculated onto the leaf surfaces of three healthy plants by blowing conidia from infected leaves with pressurized air. Non-inoculated plants were treated as control. Both the control and inoculated plants were separately placed in growth chambers under 60% humidity; light/dark, 16 h/8 h; and a temperature of 18°C. After a period of 12-15 days, the leaves of the inoculated plants exhibited signs of powdery mildew, whereas the control group remained unaffected. Therefore, the fungal pathogen was identified and confirmed as P. xanthii (isolate PXSF202310). Previously, P. xanthii was reported on Impatiens balsamina and S. farinacea from China and Korea (Zhu et al. 2021; Choi et al. 2022). As far as we know, this is the first documentation of P. xanthii on S. farinacea in central China. The presence of P. xanthii can lead to a deterioration in plant health and stunted growth, thereby negatively impacting both the decorative and medicinal value of S. farinacea. The recognition of P. xanthii on S. farinacea enhances our comprehension of this pathogen hosts and provides fundamental information for forthcoming disease control studies.

Biocontrol potential of Cladosporium sphaerospermum against the wheat powdery mildew fungus Blumeria graminis f. sp. tritici.

Cladosporium spp. are known to be mycoparasites and inhibit phytopathogenic fungi. However, so far, little information is available on the impacts of Cladosporium spp. on powdery mildews. Based on the morphological characteristics and molecular analysis, C. sphaerospermum was identified as a mycoparasite on the wheat powdery mildew fungus (Blumeria graminis f. sp. tritici, Bgt, recently named as B. graminis s. str.). C. sphaerospermum was capable of preventing colony formation and conidial distribution of Bgt. The biomasses of Bgt notably decreased by 1.3, 2.2, 3.6 and 3.8 times at 2 dpi, 4 dpi, 6 dpi and 8 dpi, respectively. In addition, biomasses of C. sphaerospermum at 2 dpi, 4 dpi, 6 dpi and 8 dpi significantly increased to 5.6, 13.9, 18.2 and 67.3 times, respectively. In vitro, C. sphaerospermum exudates significantly impaired appressorial formation of Bgt. Thus, C. sphaerospermum acts as a potential biological control agent by suppressing the formation, distribution and development of Bgt conidia and is a viable alternative for managing the wheat powdery mildew. These results suggest that C. sphaerospermum is an antagonistic parasite of the wheat powdery mildew fungus, and hence, provide new knowledge about the biological control of phytopathogenic fungi.

Integrated physio-biochemical and RNA sequencing analysis revealed mechanisms of long non-coding RNA-mediated response to cadmium toxicity in wheat.

The yield and quality of wheat (Triticum aestivum L.) is seriously affected by soil cadmium (Cd), a hazardous material to plant and human health. Long non-coding RNAs (lncRNAs) of plants are shown actively involved in response to various biotic and abiotic stresses by mediating the gene regulatory networks. However, the functions of lncRNAs in wheat against Cd stress are still obscure. Using deep strand-specific RNA sequencing, 10,044 confident novel lncRNAs in wheat roots response to Cd stress were identified. It was found that 69 lncRNA-target pairs referred to cis-acting regulation and impacted the expressions of their neighboring genes involving in Cd transport and detoxification, photosynthesis, and antioxidant defense. These findings were positively corelated with the physio-biochemical results, i.e. Cd stress affected Cd accumulation, photosynthesis system and ROS in wheat. Overexpression of lncRNA37228 (targeted to a photosystem II protein D1 coding gene), resulted in enhancing Arabidopsis thaliana resistance against Cd stress. By genome-wide identification and characterization, the possible functions of photosystem II protein gene family in wheat under Cd condition were illustrated. Our findings provide novel knowledge into the molecular mechanisms of lncRNAs-regulated wheat tolerance to Cd toxicity and lay foundations for the further studies concerning lncRNAs in food safety production.

First Report of Powdery Mildew Caused by Golovinomyces bolayi on Veronica persica in Central China.

Veronica persica, Persian speedwell, is a flowering plant belonging to the family Plantaginaceae. Due to its showy flowers, this plant is widely planted in many home gardens, city parks and universities in China. From April to June 2021, signs and symptoms of powdery mildew were found on leaves of V. persica growing on the campus of Henan Normal University, Henan Province, China. Signs initially appeared as thin white colonies and subsequently white powdery masses were abundant on the adaxial and abaxial surfaces of leaves and covered up to 99 % of the leaf area. The infected leaves showed chlorotic, deformed or senescence features. About 150 V. persica plants were monitored and more than 90 % of the plants showed these signs and symptoms. Conidiophores (n = 20) were 108 to 220 × 10 to 13 µm and composed of foot cells, followed by short cells and conidia. Conidia were hyaline, doliiform-subcylindrical shaped, 21 to 37 × 15 to 22 µm, and showed distinct fibrosin bodies. Conidial germ tubes were produced at the perihilar position. No chasmothecia were observed. The observed morphological characteristics were consistent with those of previously documented Golovinomyces bolayi (Braun and Cook 2012). To further confirm the powdery mildew fungus, structures of the pathogen were harvested and total genomic DNA was isolated using the method previously described by Zhu et al. (2019, 2021). Using the primers ITS1/ITS4, the internal transcribed spacer (ITS) region of rDNA was amplified (White et al. 1990) and the amplicon was sequenced. The resulting sequence was deposited into GenBank under Accession No. MZ343575 and was 100 % identical (592/592 bp) to G. bolayi on Kalanchoe blossfeldiana (LC417096) (Braun et al. 2019). The additional phylogenetic analysis clearly illustrated that the identified fungus and G. bolayi were clustered in the same branch (Zhu et al. 2022a; Zhu et al. 2022b). To test pathogenicity, healthy V. persica plants were collected from the campus of Henan Normal University and leaf surfaces of three plants were inoculated by dusting fungal conidia from mildew-infested leaves using pressurized air. Three plants without inoculation served as a control. The spore-treated and non-treated plants were separately placed in two growth chambers (temperature, 18℃; humidity, 60%; light/dark, 16h/8h). Seven- to eight-days post-inoculation, pathogen signs were noticeable on inoculated plants, whereas control plants remained healthy. Similar results were obtained by conducting the pathogenicity assays twice. Therefore, based on the analysis, G. bolayi was identified and confirmed as the causal agent of the powdery mildew. This pathogen has been reported on V. persica in Iran (Golmohammadi et al. 2019). However, to our best knowledge, there is no report concerning the powdery mildew caused by G. bolayi on V. persica in China. Recently, G. bolayi was segregated from species clades of G. orontii complex (Braun et al. 2019). Our record of the molecular characterization of G. bolayi will support the further phylogeny and taxonomy analysis of the G. orontii complex. The sudden outbreak of powdery mildew caused by G. bolayi on V. persica may detract from plant health and ornamental value. The identification and confirmation of this disease expands the understanding of this causal agent and will offer support for future powdery mildew control.

Jasmonic acid pretreatment improves salt tolerance of wheat by regulating hormones biosynthesis and antioxidant capacity.

Salt stress is a severe environmental factor that detrimentally affects wheat growth and production worldwide. Previous studies illustrate that exogenous jasmonic acid (JA) significantly improved salt tolerance in plants. However, little is known about the underlying molecular mechanisms of JA induced physiochemical changes in wheat seedlings under salt stress conditions. In this study, biophysiochemical and transcriptome analysis was conducted to explore the mechanisms of exogenous JA induced salt tolerance in wheat. Exogenous JA increased salt tolerance of wheat seedlings by alleviating membrane lipid oxidation, improving root morphology, enhancing the contents of ABA, JA and SA and increasing relative water content. In the RNA-seq profiles, we identified a total of 54,263 unigenes and 1,407 unigenes showed differentially expressed patterns in JA pretreated wheat seedlings exposed to salt stress comparing to those with salt stress alone. Subsequently, gene ontology (GO) and KEGG pathway enrichment analysis characterized that DEGs involved in linoleic acid metabolism and plant hormone signal transduction pathways were up-regulated predominantly in JA pretreated wheat seedlings exposed to salt stress. We noticed that genes that involved in antioxidative defense system and that encoding transcription factors were mainly up- or down-regulated. Moreover, SOD, POD, CAT and APX activities were increased in JA pretreated wheat seedlings exposed to salt stress, which is in accordance with the transcript profiles of the relevant genes. Taken together, our results demonstrate that the genes and enzymes involved in physiological and biochemical processes of antioxidant system, plant hormones and transcriptional regulation contributed to JA-mediated enhancement of salt tolerance in wheat. These findings will facilitate the elucidation of the potential molecular mechanisms associated with JA-dependent amelioration of salt stress in wheat and lay theoretical foundations for future studies concerning the improvement of plant tolerance to abiotic environmental stresses.

He-Ne laser irradiation ameliorates cadmium toxicity in wheat by modulating cadmium accumulation, nutrient uptake and antioxidant defense system.

Cadmium (Cd) is one of the most hazardous heavy metals that negatively affect the growth and yield of wheat. He-Ne laser irradiation is known to ameliorate cadmium (Cd) stress in wheat. However, the underlying mechanism of He-Ne laser irradiation on protecting wheat against Cd stress is not well recognized. In present study, Cd-treated wheat showed significant reduction in growth, root morphology and total chlorophyll content, but notably increase of Cd accumulation in both roots and shoots. However, He-Ne laser irradiation dramatically reduced concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2), and increased total chlorophyll content and activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX) in roots of wheat plants under Cd stress. Further, He-Ne laser irradiation significantly upregulated the transcripts of TaGR (glutathione reductase) and TaGST (glutathione-S-transferase) genes along with the increased activities of GR and GST and glutathione (GSH) concentration in roots of wheat seedlings under Cd stress. In addition, He-Ne laser irradiation enhanced the uptake of mineral elements (N, P, Mg, Fe, Zn and Cu), and significantly decreased Cd uptake and transport mainly through down-regulating the expressions of Cd transport genes (TaHMA2 and TaHMA3) in roots of wheat seedlings under Cd stress. Overall, these findings suggested that He-Ne laser irradiation alleviated the adverse effects of Cd on wheat growth by enhancing antioxidant defense system, improving mineral nutrient status, and decreasing the Cd uptake and transport. This study provides new insights into the roles of He-Ne laser irradiation in the amelioration of Cd stress in wheat and indicates the potential application of this irradiation in crop breeding and growth under Cd stress conditions.

Profiling of MicroRNAs Involved in Mepiquat Chloride-Mediated Inhibition of Internode Elongation in Cotton (Gossypium hirsutum L.) Seedlings.

Mepiquat chloride (MC) is the most important plant growth retardant that is widely used in cotton (Gossypium hirsutum L.) production to suppress excessive vegetative growth and improve plant architecture. MicroRNAs (miRNAs) are important gene expression regulators that control plant growth and development. However, miRNA-mediated post-transcriptional regulation in MC-induced growth inhibition remains unclear. In this study, the dynamic expression profiles of miRNAs responsive to MC in cotton internodes were investigated. A total of 508 known miRNAs belonging to 197 families and five novel miRNAs were identified. Among them, 104 miRNAs were differentially expressed at 48, 72, or 96 h post MC treatment compared with the control (0 h); majority of them were highly conserved miRNAs. The number of differentially expressed miRNAs increased with time after treatment. The expression of 14 known miRNAs was continuously suppressed, whereas 12 known miRNAs and one novel miRNA were continuously induced by MC. The expression patterns of the nine differentially expressed miRNAs were verified using qRT-PCR. The targets of the known and novel miRNAs were predicted. Four conserved and six novel targets were validated using the RLM-5' RACE assay. This study revealed that miRNAs play crucial regulatory roles in the MC-induced inhibition of internode elongation. It can improve our understanding of post-transcriptional gene regulation in MC-mediated growth inhibition and could potentially facilitate the breeding of dwarf cotton.

The Tetracentron genome provides insight into the early evolution of eudicots and the formation of vessel elements.

BACKGROUND: Tetracentron sinense is an endemic and endangered deciduous tree. It belongs to the Trochodendrales, one of four early diverging lineages of eudicots known for having vesselless secondary wood. Sequencing and resequencing of the T. sinense genome will help us understand eudicot evolution, the genetic basis of tracheary element development, and the genetic diversity of this relict species. RESULTS: Here, we report a chromosome-scale assembly of the T. sinense genome. We assemble the 1.07 Gb genome sequence into 24 chromosomes and annotate 32,690 protein-coding genes. Phylogenomic analyses verify that the Trochodendrales and core eudicots are sister lineages and showed that two whole-genome duplications occurred in the Trochodendrales approximately 82 and 59 million years ago. Synteny analyses suggest that the γ event, resulting in paleohexaploidy, may have only happened in core eudicots. Interestingly, we find that vessel elements are present in T. sinense, which has two orthologs of AtVND7, the master regulator of vessel formation. T. sinense also has several key genes regulated by or regulating TsVND7.2 and their regulatory relationship resembles that in Arabidopsis thaliana. Resequencing and population genomics reveals high levels of genetic diversity of T. sinense and identifies four refugia in China. CONCLUSIONS: The T. sinense genome provides a unique reference for inferring the early evolution of eudicots and the mechanisms underlying vessel element formation. Population genomics analysis of T. sinense reveals its genetic diversity and geographic structure with implications for conservation.

An improved method of constructing degradome library suitable for sequencing using Illumina platform.

BACKGROUND: Post-transcriptional gene regulation is one of the critical layers of overall gene expression programs and microRNAs (miRNAs) play an indispensable role in this process by guiding cleavage on the messenger RNA targets. The transcriptome-wide cleavages on the target transcripts can be identified by analyzing the degradome or PARE or GMUCT libraries. However, high-throughput sequencing of PARE or degradome libraries using Illumina platform, a widely used platform, is not so straightforward. Moreover, the currently used degradome or PARE methods utilize MmeI restriction site in the 5' RNA adapter and the resulting fragments are only 20-nt long, which often poses difficulty in distinguishing between the members of the same target gene family or distinguishing miRNA biogenesis intermediates from the primary miRNA transcripts belonging to the same miRNA family. Consequently, developing a method which can generate longer fragments from the PARE or degradome libraries which can also be sequenced easily using Illumina platform is ideal. RESULTS: In this protocol, 3' end of the 5'RNA adaptor of TruSeq small RNA library is modified by introducing EcoP15I recognition site. Correspondingly, the double-strand DNA (dsDNA) adaptor sequence is also modified to suit with the ends generated by the restriction enzyme EcoP15I. These modifications allow amplification of the degradome library by primer pairs used for small RNA library preparation, thus amenable for sequencing using Illumina platform, like small RNA library. CONCLUSIONS: Degradome library generated using this improved protocol can be sequenced easily using Illumina platform, and the resulting tag length is ~ 27-nt, which is longer than the MmeI generated fragment (20-nt) that can facilitate better accuracy in validating target transcripts belonging to the same gene family or distinguishing miRNA biogenesis intermediates of the same miRNA family. Furthermore, this improved method allows pooling and sequencing degradome libraries and small RNA libraries simultaneously using Illumina platform.

Characterization of miRNAs and their target genes in He-Ne laser pretreated wheat seedlings exposed to drought stress.

Drought stress is considered a critical environmental factor that negatively affects wheat growth and development, which causes considerable losses in wheat yields worldwide. More recently, numerous microRNAs (miRNAs) have been found to be involved in wheat responses to drought stresses. However, there is little information regarding the effects of He-Ne laser irradiation on the expression traits of miRNAs and their targets in wheat seedlings exposed to drought stress. In the current study, therefore, a combination of physiological and molecular approaches was used to assess the effect of He-Ne laser irradiation on the expression of miRNAs and their targets in wheat seedlings exposed to drought stress. Our results demonstrated that drought stress significantly reduced plant height, root length, shoot and root fresh weight, relative water content, the expression level and activity of superoxide dismutase (SOD), enhanced malondialdehyde (MDA) concentration in the wheat seedlings. However, He-Ne laser irradiation significantly enhanced the activities of SOD, ascorbate peroxidase (APX), peroxidase (POD) and relative water content, and reduced MDA concentration of seedlings by regulating gene expression for SOD, POD, APX. In addition, in comparison with drought stress alone, miR160, miR164 and miR398 transcripts were down-regulated, and expression levels of its targets auxin response factor (ARF22), NAC domain transcription factor and Cu/Zn superoxide dismutases (CSD) were up-regulated in He-Ne laser irradiated seedlings exposed to drought stress. These results suggested that He-Ne laser irradiation could possible protection of drought stress, at least partially, by increasing the transcript levels and activities of SOD, POD and APX, and decreasing the transcript levels of miR160, miR164 and miR398. To the best of our knowledge, this is the first study to present biochemical and molecular evidence supporting the effect of He-Ne laser irradiation on the alleviation of drought stress in wheat seedlings mediated by miRNA expression.

Genome-wide identification and profiling of microRNAs in Paulownia tomentosa cambial tissues in response to seasonal changes.

MicroRNAs (miRNAs), a group of endogenous small non-coding RNAs, have been shown to play essential roles in the regulation of gene expression at the post-transcriptional level. Although Paulownia tomentosa is an ecologically and economically important timber species due to its rapid growth, few efforts have focused on small RNAs (sRNAs) in the cambial tissues during winter and summer transition. In the present study, we identified 33 known miRNA families and 29 novel miRNAs which include 20 putative novel miRNAs* in P. tomentosa cambial tissues during winter and summer transition. Through differential expression analysis, we showed that 15 known miRNAs and 8 novel miRNAs were preferentially abundant in certain stage of cambial tissues. Based on the P. tomentosa mRNA transcriptome database, 1667 and 78 potential targets were predicted for 29 known and 20 novel miRNAs, respectively and the predicted targets are mostly transcription factors and functional genes. The targets of these miRNAs were enriched in "metabolic process" and "transcription regulation" by using Gene Ontology enrichment analysis. In addition, KEGG pathway analyses revealed the involvement of miRNAs in starch and sucrose metabolism and plant-pathogen interaction metabolism pathways. Noticeably, qRT-PCR expression analysis demonstrated that 9 miRNAs and their targets were existed a negative correlation in P. tomentosa cambial tissues. This study is the first to examine known and novel miRNAs and their potential targets in P. tomentosa cambial tissues during winter and summer transition and identify several candidate genes potentially regulating cambial phase transition, and thus provide a framework for further understanding of miRNAs functions in the regulation of cambial phase transition and wood formation in trees.

Physiological and transcriptome analysis of He-Ne laser pretreated wheat seedlings in response to drought stress.

Drought stress is a serious problem worldwide that reduces crop productivity. The laser has been shown to play a positive physiological role in enhancing plant seedlings tolerance to various abiotic stresses. However, little information is available about the molecular mechanism of He-Ne laser irradiation induced physiological changes for wheat adapting to drought conditions. Here, we performed a large-scale transcriptome sequencing to determine the molecular roles of He-Ne laser pretreated wheat seedlings under drought stress. There were 98.822 transcripts identified, and, among them, 820 transcripts were found to be differentially expressed in He-Ne laser pretreated wheat seedlings under drought stress compared with drought stress alone. Furthermore, most representative transcripts related to photosynthesis, nutrient uptake and transport, homeostasis control of reactive oxygen species and transcriptional regulation were expressed predominantly in He-Ne laser pretreated wheat seedlings. Thus, the up-regulated physiological processes of photosynthesis, antioxidation and osmotic accumulation because of the modified expressions of the related genes could contribute to the enhanced drought tolerance induced by He-Ne laser pretreatment. These findings will expand our understanding of the complex molecular events associated with drought tolerance conferred by laser irradiation in wheat and provide abundant genetic resources for future studies on plant adaptability to environmental stresses.

Quantification of Membrane Protein Dynamics and Interactions in Plant Cells by Fluorescence Correlation Spectroscopy.

Deciphering the dynamics of protein and lipid molecules on appropriate spatial and temporal scales may shed light on protein function and membrane organization. However, traditional bulk approaches cannot unambiguously quantify the extremely diverse mobility and interactions of proteins in living cells. Fluorescence correlation spectroscopy (FCS) is a powerful technique to describe events that occur at the single-molecule level and on the nanosecond to second timescales; therefore, FCS can provide data on the heterogeneous organization of membrane systems. FCS can also be combined with other microscopy techniques, such as super-resolution techniques. More importantly, FCS is minimally invasive, which makes it an ideal approach to detect the heterogeneous distribution and dynamics of key proteins during development. In this review, we give a brief introduction about the development of FCS and summarize the significant contributions of FCS in understanding the organization of plant cell membranes and the dynamics and interactions of membrane proteins. We also discuss the potential applications of this technique in plant biology.

Irradiation with low-dose gamma ray enhances tolerance to heat stress in Arabidopsis seedlings.

Gamma irradiation at low doses can stimulate the tolerance to environmental stress in plants. However, the knowledge regarding the mechanisms underlying the enhanced tolerance induced by low-dose gamma irradiation is far from fully understood. In this study, to investigate the physiological and molecular mechanisms of heat stress alleviated by low-dose gamma irradiation, the Arabidopsis seeds were exposed to a range of doses before subjected to heat treatment. Our results showed that 50-Gy gamma irradiation maximally promoted seedling growth in response to heat stress. The production rate of superoxide radical and contents of hydrogen peroxide and malondialdehyde in the seedlings irradiated with 50-Gy dose under heat stress were significantly lower than those of controls. The activities of antioxidant enzymes, glutathione (GSH) content and proline level in the gamma-irradiated seedlings were significantly increased compared with the controls. Furthermore, transcriptional expression analysis of selected genes revealed that some components related to heat tolerance were stimulated by low-dose gamma irradiation under heat shock. Our results suggest that low-dose gamma irradiation can modulate the physiological responses as well as gene expression related to heat tolerance, thus alleviating the stress damage in Arabidopsis seedlings.

Characterization of wheat miRNAs and their target genes responsive to cadmium stress.

A increasing number of microRNAs have been shown to play important regulatory roles in plant responses to various metal stresses. However, little information about miRNAs especially miRNAs responsive to cadmium (Cd) stress is available in wheat. To investigate the role of miRNAs in responses to Cd stress, wheat seedlings were subjected to 250 µM Cd solution for 6, 12, 24 and 48 h, and analyses of morphological and physiological changes as well as the expression of five miRNAs and their corresponding targets were carried out. Our results demonstrated that miRNAs and their targets were differentially expressed in leaves and roots of wheat seedlings exposed to Cd stress. Furthermore, miR398 may involve in oxidative stress tolerance by regulating its target CSD to participate in Cd stress. Among ten miRNA-target pairs studied, nine pairs showed complex regulation relationship in leaves and roots of wheat seedlings exposed to Cd stress. These findings suggested that miRNAs are involved in the mediation of Cd stress signaling responses in wheat. The characterization of the miRNAs and the associated targets in responses to Cd exposure provides a framework for understanding the molecular mechanism of heavy metal tolerance in plants.

MicroRNA857 Is Involved in the Regulation of Secondary Growth of Vascular Tissues in Arabidopsis.

MicroRNAs (miRNAs) are endogenous small RNAs that repress target gene expression posttranscriptionally, and are critically involved in various developmental processes and responses to environmental stresses in eukaryotes. MiRNA857 is not widely distributed in plants and is encoded by a single gene, AtMIR857, in Arabidopsis (Arabidopsis thaliana). The functions of miR857 and its mechanisms in regulating plant growth and development are still unclear. Here, by means of genetic analysis coupled with cytological studies, we investigated the expression pattern and regulation mechanism of miR857 and its biological functions in Arabidopsis development. We found that miR857 regulates its target gene, Arabidopsis LACCASE7, at the transcriptional level, thereby reducing laccase activity. Using stimulated Raman scattering and x-ray microtomography three-dimensional analyses, we showed that miR857 was involved in the regulation of lignin content and consequently morphogenesis of the secondary xylem. In addition, miR857 was activated by SQUAMOSA PROMOTER BINDING PROTEIN-LIKE7 in response to low copper conditions. Collectively, these findings demonstrate the role of miR857 in the regulation of secondary growth of vascular tissues in Arabidopsis and reveal a unique control mechanism for secondary growth based on the miR857 expression in response to copper deficiency.

Genome-wide analysis reveals dynamic changes in expression of microRNAs during vascular cambium development in Chinese fir, Cunninghamia lanceolata.

MicroRNAs (miRNAs) are small noncoding regulatory RNAs that play key roles in the process of plant development. To date, extensive studies of miRNAs have been performed in a few model plants, but few efforts have focused on small RNAs (sRNAs) in conifers because of the lack of reference sequences for their enormous genomes. In this study, Solexa sequencing of three sRNA libraries obtained from dormant, reactivating, and active vascular cambium in Chinese fir (Cunninghamia lanceolata) using tangential cryosectioning identified 20 known miRNA families and 18 novel potential miRNAs, of which nine novel miRNA precursors were validated by RT-PCR and sequencing. More than half of these novel miRNAs displayed stage-specific expression patterns in the vascular cambium. Furthermore, analysing the 103 miRNAs and their predicted targets indicated that about 70% appeared to negatively regulate their targets, of which two target genes involved in the regulation of cambial cell division were validated via RNA ligase-mediated rapid amplification of 5'-cDNA ends (RLM 5'-RACE) and transient co-expression in Nicotiana benthamiana leaves. Interestingly, miRNA156 and miRNA172 may regulate the phase transition in vascular cambium from dormancy to active growth. These results provide new insights into the important regulatory functions of miRNAs in vascular cambium development and wood formation in conifers.

Exogenous jasmonic acid can enhance tolerance of wheat seedlings to salt stress.

Jasmonic acid (JA) is regarded as endogenous regulator that plays an important role in regulating stress responses, plant growth and development. To investigate the physiological mechanisms of salt stress mitigated by exogenous JA, foliar application of 2mM JA was done to wheat seedlings for 3days and then they were subjected to 150mM NaCl. Our results showed that 150mM NaCl treatment significantly decreased plant height, root length, shoot dry weight, root dry weight, the concentration of glutathione (GSH), chlorophyll b (Chl b) and carotenoid (Car), the activities of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), enhanced the concentration of malondialdehyde (MDA), hydrogen peroxide (H2O2) and the rate of superoxide radical (O2•-) generation in the wheat seedlings when compared with the control. However, treatments with exogenous JA for 3 days significantly enhanced salt stress tolerance in wheat seedlings by decreasing the concentration of MDA and H2O2, the production rate of O2•- and increasing the transcript levels and activities of SOD, POD, CAT and APX and the contents of GSH, Chl b and Car, which, in turn, enhanced the growth of salt stressed seedlings. These results suggested that JA could effectively protect wheat seedlings from salt stress damage by enhancing activities of antioxidant enzymes and the concentration of antioxidative compounds to quench the excessive reactive oxygen species caused by salt stress and presented a practical implication for wheat cultivation in salt-affected soils.

The regulation of cambial activity in Chinese fir (Cunninghamia lanceolata) involves extensive transcriptome remodeling.

Chinese fir (Cunninghamia lanceolata), a commercially important tree for the timber and pulp industry, is widely distributed in southern China and northern Vietnam, but its large and complex genome has hindered the development of genomic resources. Few efforts have focused on analysis of the modulation of transcriptional networks in vascular cambium during the transition from active growth to dormancy in conifers. Here, we used Illumina sequencing to analyze the global transcriptome alterations at the different stages of vascular cambium development in Chinese fir. By analyzing dynamic changes in the transcriptome of vascular cambium based on our RNA sequencing (RNA-Seq) data at the dormant, reactivating and active stages, many potentially interesting genes were identified that encoded putative regulators of cambial activity, cell division, cell expansion and cell wall biosynthesis and modification. In particular, the genes involved in transcriptional regulation and hormone signaling were highlighted to reveal their biological importance in the cambium development and wood formation. Our results reveal the dynamics of transcriptional networks and identify potential key components in the regulation of vascular cambium development in Chinese fir, which will contribute to the in-depth study of cambial differentiation and wood-forming candidate genes in conifers.