Unraveling the Contribution of MulSOS2 in Conferring Salinity Tolerance in Mulberry (Morus atropurpurea Roxb).

Salinity is one of the most serious threats to sustainable agriculture. The Salt Overly Sensitive (SOS) signaling pathway plays an important role in salinity tolerance in plants, and the SOS2 gene plays a critical role in this pathway. Mulberry not only has important economic value but also is an important ecological tree species; however, the roles of the SOS2 gene associated with salt stress have not been reported in mulberry. To gain insight into the response of mulberry to salt stress, SOS2 (designated MulSOS2) was cloned from mulberry (Morus atropurpurea Roxb), and sequence analysis of the amino acids of MulSOS2 showed that it shares some conserved domains with its homologs from other plant species. Our data showed that the MulSOS2 gene was expressed at different levels in different tissues of mulberry, and its expression was induced substantially not only by NaCl but also by ABA. In addition, MulSOS2 was exogenously expressed in Arabidopsis, and the results showed that under salt stress, transgenic MulSOS2 plants accumulated more proline and less malondialdehyde than the wild-type plants and exhibited increased tolerance to salt stress. Moreover, the MulSOS2 gene was transiently overexpressed in mulberry leaves and stably overexpressed in the hairy roots, and similar results were obtained for resistance to salt stress in transgenic mulberry plants. Taken together, the results of this study are helpful to further explore the function of the MulSOS2 gene, which provides a valuable gene for the genetic breeding of salt tolerance in mulberry.

Integrated Analysis of lncRNAs and mRNAs Reveals Complex Gene Network Mediated by lncRNAs and Regulatory Function of MuLRR-RLK-AS in Response to Phytoplasma Infection in Mulberry.

Phytoplasma disease is one of the most serious infectious diseases that affects the growth and development of mulberry. Long non-coding RNAs (lncRNAs) play an important role in plants' defense systems; however, the contribution of lncRNAs in the response to phytoplasma infection in mulberry is still largely unknown. Herein, strand-specific RNA sequencing was performed to profile the mRNAs and lncRNAs involved in the response to phytoplasma infection in mulberry, and a total of 4169 genes were found to be differentially expressed (DE) between healthy and phytoplasma-infected leaves. Moreover, 1794 lncRNAs were identified, of which 742 lncRNAs were DE between healthy and infected leaves. Target prediction showed that there were 68 and 44 DE lncRNAs which may function as cis and trans-regulators, targeting 54 and 44 DE genes, respectively. These DE target genes are associated with biological processes such as metabolism, signaling, development, transcriptional regulation, etc. In addition, it was found that the expression of the antisense lncRNA (MuLRR-RLK-AS) of the leucine-rich repeat receptor-like protein kinase gene (MuLRR-RLK) was decreased in the phytoplasma-infected leaves. Interestingly, it was found that overexpression of MuLRR-RLK-AS can inhibit the expression of MuLRR-RLK. Moreover, it was found that the expression levels of PTI-related and MAPK genes in the transgenic MuLRR-RLK Arabidopsis plants were significantly higher than those in the wild-type plants when inoculated with pathogens, and the transgenic plants were conferred with strong disease resistance. Our results demonstrate that MuLRR-RLK-AS, as a trans-regulatory factor, can inhibit the expression of the MuLRR-RLK gene and is a negative regulatory factor for mulberry resistance. The information provided is particularly useful for understanding the functions and mechanisms of lncRNAs in the response to phytoplasma infection in mulberry.

MAPKKKs in Plants: Multidimensional Regulators of Plant Growth and Stress Responses.

Mitogen-activated protein kinase kinase kinase (MAPKKK, MAP3K) is located upstream of the mitogen-activated protein kinase (MAPK) cascade pathway and is responsible for receiving and transmitting external signals to the downstream MAPKKs. Although a large number of MAP3K genes play important roles in plant growth and development, and response to abiotic and biotic stresses, only a few members' functions and cascade signaling pathways have been clarified, and the downstream MAPKKs and MAPKs of most MAP3Ks are still unknown. As more and more signaling pathways are discovered, the function and regulatory mechanism of MAP3K genes will become clearer. In this paper, the MAP3K genes in plants were classified and the members and basic characteristics of each subfamily of MAP3K were briefly described. Moreover, the roles of plant MAP3Ks in regulating plant growth and development and stress (abiotic and biotic) responses are described in detail. In addition, the roles of MAP3Ks involved in plant hormones signal transduction pathway were briefly introduced, and the future research focus was prospected.

Maize HEAT UP-REGULATED GENE 1 plays vital roles in heat stress tolerance.

Increasing temperature is one of the major threats to maize growth and yield globally. Under heat stress conditions, intracellular protein homeostasis is seriously disturbed, leading to accumulation of abnormally folded proteins, especially in the endoplasmic reticulum (ER). Molecular chaperones are vital players in the renaturation process and in preventing protein aggregation. However, heat stress tolerance-associated chaperones are not well documented in maize. Here, we characterized the biological roles of HEAT UP-REGULATED GENE 1 (ZmHUG1) in maize. ZmHUG1 encodes a heat-inducible holdase-type molecular chaperone localized in the ER. Knockout mutant of ZmHUG1 exhibited remarkably enhanced sensitivity to heat stress. Accordingly, the zmhug1 mutant showed severe ER stress under high temperature. MAIZE PRENYLATED RAB ACCEPTOR 1.C1 (ZmPRA1.C1) was identified as a client of ZmHUG1, and heat-induced aggregation of ZmPRA1.C1 was accelerated in the zmhug1 mutant. Furthermore, the expression of ZmHUG1 was rapidly transactivated by ER stress sensor BASIC LEUCINE ZIPPER DOMAIN 60 (bZIP60) when heat stress occurred. This study reveals a ZmHUG1-based thermo-protective mechanism in maize.

Characterization of GABA-Transaminase Gene from Mulberry (Morus multicaulis) and Its Role in Salt Stress Tolerance.

Gamma-aminobutyric acid (GABA) has been reported to accumulate in plants when subjected to salt stress, and GABA-transaminase (GABA-T) is the main GABA-degrading enzyme in the GABA shunt pathway. So far, the salt tolerance mechanism of the GABA-T gene behind the GABA metabolism remains unclear. In this study, the cDNA (designated MuGABA-T) of GABA-T gene was cloned from mulberry, and our data showed that MuGABA-T protein shares some conserved characteristics with its homologs from several plant species. MuGABA-T gene was constitutively expressed at different levels in mulberry tissues, and was induced substantially by NaCl, ABA and SA. In addition, our results demonstrated that exogenous application of GABA significantly reduced the salt damage index and increased plant resistance to NaCl stress. We further performed a functional analysis of MuGABA-T gene and demonstrated that the content of GABA was reduced in the transgenic MuGABA-T Arabidopsis plants, which accumulated more ROS and exhibited more sensitivity to salt stress than wild-type plants. However, exogenous application of GABA significantly increased the activities of antioxidant enzymes and alleviated the active oxygen-related injury of the transgenic plants under NaCl stress. Moreover, the MuGABA-T gene was overexpressed in the mulberry hairy roots, and similar results were obtained for sensitivity to salt stress in the transgenic mulberry plants. Our results suggest that the MuGABA-T gene plays a pivotal role in GABA catabolism and is responsible for a decrease in salt tolerance, and it may be involved in the ROS pathway in the response to salt stress. Taken together, the information provided here is helpful for further analysis of the function of GABA-T genes, and may promote mulberry resistance breeding in the future.

MicroRNA Profiling During Mulberry (Morus atropurpurea Roxb) Fruit Development and Regulatory Pathway of miR477 for Anthocyanin Accumulation.

To understand the mechanism of small non-coding RNAs (miRNA)-mediated development and ripening of mulberry fruits, three small RNA libraries from mulberry fruits at different development stages were constructed, and 159 conserved miRNAs as well as 86 novel miRNAs were successfully identified. Among the miRNAs identified, there were 90 miRNAs which showed differential expression patterns at different stages of fruit development and ripening. The target genes of these differential expressed (DE) miRNAs were involved in growth and development, transcription and regulation of transcription, metabolic processes, and etc. Interestingly, it was found that the expression level of mul-miR477 was increased with fruit ripening, and it can target the antisense lncRNA (Mul-ABCB19AS) of the ATP binding cassette (ABC) transporter B 19 gene (Mul-ABCB19). Our results showed that mul-miR477 can repress the expression of Mul-ABCB19AS and increase the expression of Mul-ABCB19, and it acted as a positive regulator participating anthocyanin accumulation through the regulatory network of mul-miR477-Mul-ABCB19AS-Mul-ABCB19.

Transcriptome and DNA Methylome Reveal Insights Into Phytoplasma Infection Responses in Mulberry (Morus multicaulis Perr.).

To reveal whether the response of mulberry to phytoplasma infection is associated with genome-wide DNA methylation changes, the methylome and transcriptome patterns of mulberry in response to phytoplasma infection were explored. Though the average methylation level of the infected leaves showed no significant difference from that of healthy leaves, there were 1,253 differentially methylated genes (DMGs) and 1,168 differentially expressed genes (DEGs) in the infected leaves, and 51 genes were found simultaneously to be differently methylated and expressed. It was found that the expression of G-type lectin S-receptor-like serine/threonine protein kinase gene (Mu-GsSRK) was increased, but its methylation level was decreased in the pathogen-infected or salicylic acid (SA)-treated leaves. Overexpression of Mu-GsSRK in Arabidopsis and in the hairy roots of mulberry enhanced transgenic plant resistance to the phytoplasma. Moreover, overexpression of Mu-GsSRK enhanced the expressions of pathogenesis-related protein 1, plant defensin, and cytochrome P450 protein CYP82C2 genes in transgenic plants inoculated with pathogens, which may contribute to the enhanced disease resistance against various pathogens. Finally, the DNA methylation dynamic patterns and functions of the differentially expressed and methylated genes were discussed. The results suggested that DNA methylation has important roles in mulberry responses to phytoplasma infection.

Characterization of NPR1 and NPR4 genes from mulberry (Morus multicaulis) and their roles in development and stress resistance.

The quality and quantity of mulberry leaves are often affected by various environmental factors. The plant NPR1 and its homologous genes are important for plant systemic acquired resistance. Here, the full-length cDNAs encoding the NPR1 and NPR4 genes (designated MuNPR1 and MuNPR4, respectively) were isolated from Morus multicaulis. Sequence analysis of the amino acids and protein modeling of the MuNPR1 and MuNPR4 proteins showed that MuNPR1 shares some conserved characteristics with its homolog MuNPR4. MuNPR1 was shown to have different expression patterns than MuNPR4 in mulberry plants. Interestingly, MuNPR1 or MuNPR4 transgenic Arabidopsis produced an early flowering phenotype, and the expression of the pathogenesis-related 1a gene was promoted in MuNPR1 transgenic Arabidopsis. The MuNPR1 transgenic plants showed more resistance to Pseudomonas syringae pv. tomato DC3000 (Pst. DC3000) than did the wild-type Arabidopsis. Moreover, the ectopic expression of MuNPR1 might lead to enhanced scavenging ability and suppress collase accumulation. In contrast, the MuNPR4 transgenic Arabidopsis were hypersensitive to Pst. DC3000 infection. In addition, transgenic Arabidopsis with the ectopic expression of either MuNPR1 or MuNPR4 showed sensitivity to salt and drought stresses. Our data suggest that both the MuNPR1 and MuNPR4 genes play a role in the coordination between signaling pathways, and the information provided here enables the in-depth functional analysis of the MuNPR1 and MuNPR4 genes and may promote mulberry resistance breeding in the future.

A Novel LncRNA, MuLnc1, Associated With Environmental Stress in Mulberry (Morus multicaulis).

Environmental stresses are major constraints that limit the leaf productivity and quality of mulberry. LncRNAs have emerged as important regulators in response to biotic and abiotic stresses in plants. However, the functions and mechanisms of most lncRNAs remain largely unknown. A novel lncRNA designated as MuLnc1 was found to be cleaved by mul-miR3954 and produce secondary siRNAs in a 21 nt phase in mulberry. It was demonstrated that one of the siRNAs produced, si161579, can silence the expression of the calmodulin-like protein gene CML27 of mulberry (MuCML27). When MuCML27 was heterologously expressed in Arabidopsis, the transgenic plants exhibited enhanced resistance to Botrytis cinerea and Pseudomonas syringae pv tomato DC3000. In addition, the transgenic MuCML27-overexpressing Arabidopsis plants are more tolerant to salt and drought stresses. Furthermore, the network of mul-miR3954-MuLnc1-siRNAs-mRNAs was modeled to elucidate the interaction between lncRNAs and sRNAs with mRNAs. All of these, taken together, suggest that MuLnc1 was associated with environmental stress in mulberry and may be considered as a potential genetic improvement target gene of mulberry. The information provided may shed light on the complicated gene expression regulatory mechanisms in mulberry stress responses.

Integrated Phloem Sap mRNA and Protein Expression Analysis Reveals Phytoplasma-infection Responses in Mulberry.

To gain insight into the response of mulberry to phytoplasma-infection, the expression profiles of mRNAs and proteins in mulberry phloem sap were examined. A total of 955 unigenes and 136 proteins were found to be differentially expressed between the healthy and infected phloem sap. These differentially expressed mRNAs and proteins are involved in signaling, hormone metabolism, stress responses, etc. Interestingly, we found that both the mRNA and protein levels of the major latex protein-like 329 (MuMLPL329) gene were increased in the infected phloem saps. Expression of the MuMLPL329 gene was induced by pathogen inoculation and was responsive to jasmonic acid. Ectopic expression of MuMLPL329 in Arabidopsis enhances transgenic plant resistance to Botrytis cinerea, Pseudomonas syringae pv tomato DC3000 (Pst. DC3000) and phytoplasma. Further analysis revealed that MuMLPL329 can enhance the expression of some defense genes and might be involved in altering flavonoid content resulting in increased resistance of plants to pathogen infection. Finally, the roles of the differentially expressed mRNAs and proteins and the potential molecular mechanisms of their changes were discussed. It was likely that the phytoplasma-responsive mRNAs and proteins in the phloem saps were involved in multiple pathways of mulberry responses to phytoplasma-infection, and their changes may be partially responsible for some symptoms in the phytoplasma infected plants.

MiRNA-seq-based profiles of miRNAs in mulberry phloem sap provide insight into the pathogenic mechanisms of mulberry yellow dwarf disease.

A wide range of miRNAs have been identified as phloem-mobile molecules that play important roles in coordinating plant development and physiology. Phytoplasmas are associated with hundreds of plant diseases, and the pathogenesis involved in the interactions between phytoplasmas and plants is still poorly understood. To analyse the molecular mechanisms of phytoplasma pathogenicity, the miRNAs profiles in mulberry phloem saps were examined in response to phytoplasma infection. A total of 86 conserved miRNAs and 19 novel miRNAs were identified, and 30 conserved miRNAs and 13 novel miRNAs were differentially expressed upon infection with phytoplasmas. The target genes of the differentially expressed miRNAs are involved in diverse signalling pathways showing the complex interactions between mulberry and phytoplasma. Interestingly, we found that mul-miR482a-5p was up-regulated in the infected phloem saps, and grafting experiments showed that it can be transported from scions to rootstock. Based on the results, the complexity and roles of the miRNAs in phloem sap and the potential molecular mechanisms of their changes were discussed. It is likely that the phytoplasma-responsive miRNAs in the phloem sap modulate multiple pathways and work cooperatively in response to phytoplasma infection, and their expression changes may be responsible for some symptoms in the infected plants.

The Latex Protein MLX56 from Mulberry (Morus multicaulis) Protects Plants against Insect Pests and Pathogens.

Biotic stresses are major constraints limiting the leaf quality and productivity of mulberry. MLX56 is a unique chitin-binding protein isolated from Shin-Ichinose (Morus alba) latex that displays toxicity against lepidopteran caterpillars. In this study, the full-length cDNA encoding MLX56 was isolated from Husang 32 (M. multicaulis) and designated HMLX56. Amino acid sequence analysis and protein modeling of three MLX56 proteins showed that they were highly conserved among Morus species. Tissue expression pattern analysis showed that the HMLX56 gene was strongly expressed in mulberry bark and leaves but only slightly expressed in fruits. In addition, analysis of GUS expression indicated that the promoter of HMLX56 showed higher transcriptional activity along the vascular strands, and its activity can be regulated by various environmental factors. Like the MLX56 protein from M. alba, the HMLX56 protein showed toxicity to Plutella xylostella. Moreover, when the HMLX56 gene was ectopically expressed in Arabidopsis, the transgenic plants showed enhanced resistance to aphids, the fungal pathogen Botrytis cinerea and the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. Our data suggest that the HMLX56 protein has a lectin-like molecular structure consisting of two hevein-like chitin-binding domains which provide not only chitin-binding activities but also other mechanisms of defense. The information provided here improves our understanding of the potential functions and defense mechanisms of MLX56 proteins, enabling in-depth functional analysis of latex exudates and perhaps facilitating mulberry genetic improvement in the future.

Analysis of phytoplasma-responsive sRNAs provide insight into the pathogenic mechanisms of mulberry yellow dwarf disease.

The yellow dwarf disease associated with phytoplasmas is one of the most devastating diseases of mulberry and the pathogenesis involved in the disease is poorly understood. To analyze the molecular mechanisms mediating gene expression in mulberry-phytoplasma interaction, the comprehensive sRNA changes of mulberry leaf in response to phytoplasma-infection were examined. A total of 164 conserved miRNAs and 23 novel miRNAs were identified, and 62 conserved miRNAs and 13 novel miRNAs were found to be involved in the response to phytoplasma-infection. Meanwhile, target genes of the responsive miRNAs were identified by sequencing of the degradome library. In addition, the endogenous siRNAs were sequenced, and their expression profiles were characterized. Interestingly, we found that phytoplasma infection induced the accumulation of mul-miR393-5p which was resulted from the increased transcription of MulMIR393A, and mul-miR393-5p most likely initiate the biogenesis of siRNAs from TIR1 transcript. Based on the results, we can conclude that phytoplasma-responsive sRNAs modulate multiple hormone pathways and play crucial roles in the regulation of development and metabolism. These responsive sRNAs may work cooperatively in the response to phytoplasma-infection and be responsible for some symptoms in the infected plants.

Metabolomic analysis reveals the potential metabolites and pathogenesis involved in mulberry yellow dwarf disease.

To analyse the molecular mechanisms of phytoplasma pathogenicity, the comprehensive metabolomic changes of mulberry leaf and phloem sap in response to phytoplasma infection were examined using gas chromatography-mass spectrometry. The metabolic profiles obtained revealed that the metabolite compositions of leaf and phloem sap were different, and phytoplasma infection has a greater impact on the metabolome of phloem sap than of leaf. Phytoplasma infection brought about the content changes in various metabolites, such as carbohydrates, amino acids, organic acids, etc. Meanwhile, the results of biochemical analysis showed that the degradation of starch was repressed, and the starch content was increased in the infected leaves. In addition, we found that phytoplasma infection changed the levels of abscisic acid and cytokinin and break phytohormone balance. Interestingly, our data showed that the contents of H2O2 and superoxide were increased in the infected leaves, but not in the phloem saps. Based on the results, the expression levels of the genes involved in the metabolism of some changed metabolites were examined, and the potential molecular mechanisms of these changes were discussed. It can be concluded that both the leaf and phloem saps have a complicated metabolic response to phytoplasma infection, but their response mechanisms were different.

Phytoplasma proteomic analysis.

Proteome analysis is becoming a powerful tool in the functional characterization of organisms, and takes a broad, comprehensive, systematic approach to understanding biology. Following the sequencing of the phytoplasma genomes, the next step is to characterize the expressed proteome of phytoplasmas to acquire the verification and functional annotation of all predicted genes and their protein products. Here, we describe the protocol of mulberry dwarf phytoplasma purification, phytoplasma protein extraction and separation by SDS-PAGE, in-gel tryptic digestion of the proteins, separation of the digested peptides by liquid chromatography, and identification of the peptides by mass spectrometry. The protocol described here is also applicable to the analysis of other phytoplasma proteomes.

A novel late embryogenesis abundant like protein associated with chilling stress in Nicotiana tabacum cv. bright yellow-2 cell suspension culture.

Low temperature is one of the major abiotic stresses limiting the productivity and geographical distribution of many important crops. To identify proteins associated with chilling stress in Nicotiana tabacum cv. bright yellow-2 (BY-2) cell suspension culture, we utilized a proteomic approach with two-dimensional electrophoresis to compare proteins from samples of treated with or without chilling treatment at 4 °C. One protein specifically more abundant in chilling treated sample was identified and designated as NtLEA7-3. Rapid amplification of cDNA ends gave rise to a full-length NtLEA7-3 cDNA with a complete open reading frame of 1267 bp, encoding a 322 amino acid polypeptide. Homology search and sequence multi-alignment demonstrated that the deduced NtLEA7-3 protein sequence shared a high identity with LEA-like proteins from other plants. Subcellular localization analysis indicated that the NtLEA7-3 was localized exclusively in the nucleus. When the gene was overexpressed in bright yellow-2 cells, the transgenic bright yellow-2 cells show more resistant to chilling stress than the wild-type cells. In addition, transgenic Arabidopsis plants overexpressing the NtLEA7-3 are much more resistant to cold, drought, and salt stresses. Interestingly, the expression of NtLEA7-3 in tobacco was not tissue-specific and induced by chilling, drought and salt stresses. All of these, taken together, suggest that NtLEA7-3 is worthwhile to elucidate the contribution of the proteins to the tolerance mechanism to chilling stress, and can be considered as a potential target for crop genetic improvement in the future.

Colonization of Morus alba L. by the plant-growth-promoting and antagonistic bacterium Burkholderia cepacia strain Lu10-1.

BACKGROUND: Anthracnose, caused by Colletotrichum dematium, is a serious threat to the production and quality of mulberry leaves in susceptible varieties. Control of the disease has been a major problem in mulberry cultivation. Some strains of Burkholderia cepacia were reported to be useful antagonists of plant pests and could increase the yields of several crop plants. Although B. cepacia Lu10-1 is an endophytic bacterium obtained from mulberry leaves, it has not been deployed to control C. dematium infection in mulberry nor its colonization patterns in mulberry have been studied using GFP reporter or other reporters. The present study sought to evaluate the antifungal and plant-growth-promoting properties of strain Lu10-1, to clarify its specific localization within a mulberry plant, and to better understand its potential as a biocontrol and growth-promoting agent. RESULTS: Lu10-1 inhibited conidial germination and mycelial growth of C. dematium in vitro; when applied on leaves or to the soil, Lu10-1 also inhibited the development of anthracnose in a greenhouse, but the effectiveness varied with the length of the interval between the strain treatment and inoculation with the pathogen. Strain Lu10-1 could survive in both sterile and non-sterile soils for more than 60 days. The strain produced auxins, contributed to P solubilization and nitrogenase activity, and significantly promoted the growth of mulberry seedlings. The bacteria infected mulberry seedlings through cracks formed at junctions of lateral roots with the main root and in the zone of differentiation and elongation, and the cells were able to multiply and spread, mainly to the intercellular spaces of different tissues. The growth in all the tissues was around 1-5 × 105 CFU per gram of fresh plant tissue. CONCLUSIONS: Burkholderia cepacia strain Lu10-1 is an endophyte that can multiply and spread in mulberry seedlings rapidly and efficiently. The strain is antagonistic to C. dematium and acts as an efficient plant-growth-promoting agent on mulberry seedlings and is therefore a promising candidate as a biocontrol and growth-promoting agent.

Shotgun proteomic analysis of mulberry dwarf phytoplasma.

BACKGROUND: Mulberry dwarf (MD), which is caused by phytoplasma, is one of the most serious infectious diseases of mulberry. Phytoplasmas have been associated with diseases in several hundred plant species. The inability to culture phytoplasmas in vitro has hindered their characterization at the molecular level. Though the complete genomes of two phytoplasmas have been published, little information has been obtained about the proteome of phytoplasma. Therefore, the proteomic information of phytoplasmas would be useful to elucidate the functional mechanisms of phytoplasma in many biological processes. RESULTS: MD phytoplasmas, which belong to the 16SrI-B subgroup based on the 16S DNA analysis, were purified from infected tissues using a combination of differential centrifugation and density gradient centrifugation. The expressed proteome of phytoplasma was surveyed by one-dimensional SDS-PAGE and nanocapillary liquid chromatography-tandem mass spectrometry. A total of 209 phytoplasma proteins were unambiguously assigned, including the proteins with the functions of amino acid biosynthesis, cell envelope, cellular processes, energy metabolism, nucleosides and nucleotide metabolism, replication, transcription, translation, transport and binding as well as the proteins with other functions. In addition to these known function proteins, 63 proteins were annotated as hypothetical or conserved hypothetical proteins. CONCLUSIONS: Taken together, a total of 209 phytoplasma proteins have been experimentally verified, representing the most extensive survey of any phytoplasma proteome to date. This study provided a valuable dataset of phytoplasma proteins, and a better understanding of the energy metabolism and virulence mechanisms of MD phytoplasma.

Comparative proteomic analysis provides new insights into mulberry dwarf responses in mulberry (Morus alba L.).

Mulberry dwarf (MD) is a serious infectious disease of mulberry caused by phytoplasma. Infection with MD phytoplasma results in stress phenotypes of yellowing, phyllody, stunting, proliferation, and witches' broom. Physiological and biochemical analysis has shown that infection with MD phytoplasma causes an increase in soluble carbohydrate and starch content, and a decrease in the net photosynthesis rate, carboxylation efficiency, and pigment content of leaves. Furthermore, damage to the chloroplast ultrastructure was detected in infected leaves. To better understand the pathogen-stress response of mulberry (Morus alba L.) to MD phytoplasma, we conducted a comparative proteomic analysis using 2-DE of infected and healthy leaves. Among 500 protein spots that were reproducibly detected, 20 were down-regulated and 17 were up-regulated. MS identified 16 differentially expressed proteins. The photosynthetic proteins rubisco large subunit, rubisco activase, and sedoheptulose-1,7-bisphosphatase showed enhanced degradation in infected leaves. Based these results, a model for the occurrence mechanism of MD is proposed. In conclusion, this study provides new insights into the mulberry response to MD phytoplasma infection.

Molecular cloning and characterization of an inducible RNA-dependent RNA polymerase gene, GhRdRP, from cotton (Gossypium hirsutum L.).

The RNA-dependent RNA polymerase (RdRP) cDNA, designated as Gossypium hirsutum RdRP (GhRdRP) was cloned from cotton by rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR). The full-length cDNA was 3,672 bp in size and encoded an open reading frame (ORF) of 1,110 amino acids which contained the RdRP conserved functional domain and the signature motif DbDGD. Amino acid sequence alignment indicated that GhRdRP shared the highest identity (66.37%) with AtRdRP1 and had homology with other plant, fungal, yeast and nematode RdRPs. The corresponding genomic DNA containing five exons and four introns, was isolated and analyzed. Also a 5'-flanking region was cloned, and a group of putative cis-acting elements were identified. Southern blot analysis revealed a single copy of the GhRdRP gene in cotton genome. The expression analysis by semi-quantitative RT-PCR showed that GhRdRP was induced by salicylic acid (SA), 5-chloroSA (5-CSA) and fungal infection of Rhizoctonia solani Kuhn. The cloning and characterization of the GhRdRP gene will be useful for further studies of biological roles of GhRdRP in plants.