Unveiling common and specific features of the COMPASS-like complex in sorghum.

The COMPASS-like complex, responsible for depositing H3K4 methylation, exhibits a conserved composition across yeast, plants, and animals, with functional analysis highlighting its crucial roles in plant development and stress response. In this study, we identified nine genes encoding four subunits of the COMPASS-like complex through homologous search. Phylogenetic analysis revealed the presence of two additional ASH2 genes in the sorghum genome, specifically expressed in endosperms, suggesting the formation of a unique COMPASS-like complex in sorghum endosperms. Y2H and BiFC protein-protein interaction tests demonstrated the interaction between SbRbBP5 and SbASH2A/B/C, while the association between other subunits appeared weak, possibly due to sequence variations in SbWDR5 or synergistic interactions among COMPASS-like complex subunits. The interaction between ATX1 and the C-Terminal Domain (CTD) of Pol II, reported in Arabidopsis, was not detected in sorghum. However, we made the novel discovery of transcriptional activation activity in RbBP5, which is conserved in sorghum, rice, and Arabidopsis, providing valuable insights into the mechanism by which the COMPASS-like complex regulates gene expression in plants.

Transcriptome analysis of Artemisia argyi following methyl jasmonate (MeJA) treatment and the mining of genes related to the stress resistance pathway.

Artemisia argyi Lev. et Vant. (A. argyi) is a perennial grass in the Artemisia family, the plant has a strong aroma. Methyl jasmonate (MeJA) is critical to plant growth and development, stress response, and secondary metabolic processes. The experimental material Artemisia argyi was utilized in this study to investigate the treatment of A. argyi with exogenous MeJA at concentrations of 100 and 200 µmol/L for durations of 9 and 24 h respectively. Transcriptome sequencing was conducted using the Illumina HiSeq platform to identify stress resistance-related candidate genes. Finally, a total of 102.43 Gb of data were obtained and 162,272 unigenes were identified. Differential analysis before and after MeJA treatment resulted in the screening of 20,776 differentially expressed genes. The GO classification revealed that the annotated unigenes were categorized into three distinct groups: cellular component, molecular function, and biological process. Notably, binding, metabolic process, and cellular process emerged as the most prevalent categories among them. The results of KEGG pathway statistical analysis revealed that plant hormone signal transduction, MAPK signaling pathway-plant, and plant-pathogen interaction were significant transduction pathways in A. argyi's response to exogenous MeJA-induced abiotic stress. With the alteration of exogenous MeJA concentration and duration, a significant upregulation was observed in the expression levels of calmodulin CaM4 (ID: EVM0136224) involved in MAPK signaling pathway-plant and auxin response factor ARF (ID: EVM0055178) associated with plant-pathogen interaction. The findings of this study establish a solid theoretical foundation for the future development of highly resistant varieties of A. argyi.

Dual impact of ambient humidity on the virulence of Magnaporthe oryzae and basal resistance in rice.

Humidity is a critical environmental factor affecting the epidemic of plant diseases. However, it is still unclear how ambient humidity affects the occurrence of diseases in plants. In this study, we show that high ambient humidity enhanced blast development in rice plants under laboratory conditions. Furthermore, we found that high ambient humidity enhanced the virulence of Magnaporthe oryzae by promoting conidial germination and appressorium formation. In addition, the results of RNA-sequencing analysis and the ethylene content assessment revealed that high ambient humidity suppressed the accumulation of ethylene and the activation of ethylene signaling pathway induced by M. oryzae in rice. Knock out of ethylene signaling genes OsEIL1 and OsEIN2 or exogenous application of 1-methylcyclopropene (ethylene inhibitor) and ethephon (ethylene analogues) eliminated the difference of blast resistance between the 70% and 90% relative humidity conditions, suggesting that the activation of ethylene signaling contributes to humidity-modulated basal resistance against M. oryzae in rice. In conclusion, our results demonstrated that high ambient humidity enhances the virulence of M. oryzae and compromises basal resistance by reducing the activation of ethylene biosynthesis and signaling in rice. Results from this study provide cues for novel strategies to control rice blast under global environmental changes.

Genome-wide identification of chromatin regulators in Sorghum bicolor.

Chromatin regulators play important roles in plant development and stress response. In this study, we identified totally 231 chromatin regulators including 63 histones, 29 histone chaperones, 101 histone modification enzymes, and 38 chromatin remodeling factors from Sorghum bicolor (L.) Moench. Most of these chromatin regulators are homologous to their counterparts in Arabidopsis or rice. However, sorghum genome evolves a few novel histone variants specific to some grass species and a sorghum-unique chromatin remodeling factor that contain the domains belonging to the elongation factor EF-Tu and the histone chaperone SPT16. Finally, we performed co-expression analysis for the chromatin regulator-encoding genes by clustering the expression patterns of these genes. Our results provide useful information for the future studies on the mechanism of epigenetic regulation in sorghum and its roles in development and stress response. Supplementary Information: The online version contains supplementary material available at 10.1007/s13205-022-03181-8.

Molecular identification and expression analysis of five sucrose synthase genes in Sorghum Bicolor.

In higher plants, sucrose synthase (Susy, EC 2.4.1.13) as an enzyme with a core function, involved in the synthesis and breakdown of sugars, and plays an important role in growth and metabolism. Although, the different genes encoding Susy isozyme proteins have been cloned and functionally verified in several plant species, to date detailed information about the Susy genes is lacking in Sorghum. Here, we demonstrated the identification of five novel Susy genes from the sorghum genome database. Sequence, structure and phylogenetic analyses of these five SbSusy genes revealed evolutionary conservation through Susy gene family members across Sorghum and other crop plants. The expression of sorghum Susy genes was investigated via transcriptome database in various developmental stages and different tissues. Further qRT-PCR was performed to reveal the induction of SbSusy genes under salt, drought and sugar induction. The results indicated that all Susy genes were differentially expressed in various tissues and highly associated with sucrose metabolism. This study shows a theoretical reference of Susy genes in Sorghum, which provides new insights for the knowledge of the evolution relationships, and basic information to help clarify the molecular mechanism of Susy synthase genes in Sorghum. Supplementary Information: The online version contains supplementary material available at 10.1007/s12298-022-01166-8.

Transcriptomic analysis reveals process of autolysis of Kluyveromyces marxianus in vacuum negative pressure and the higher temperature.

Kluyveromyces marxianus is expected to be used in the production of yeast extracts due to its good fermentation ability and nutritional properties. Yeast autolysis is a key process to produce yeast extract and vacuum negative pressure stress can be used as an effective way to assist autolysis. However, the molecular mechanism of initiating Kluyveromyces marxianus autolysis induced by vacuum negative pressure and the higher temperature is still unclear. In this study, RNA-seq technology was performed mainly to analyze autolytic processes in Kluyveromyces marxianus strains. Considerable differentially expressed genes (DEGs) of downregulation were significantly enriched in 7 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related to synthesis and transport of RNA and ribosome, which indicated that abnormal protein translations had already occurred in autolytic process. Interestingly, due to obvious change of related DEGs, endoplasmic reticulum-associated degradation (ERAD) and autophagy were activated and cell wall integrity pathway was hindered. Under the continuous influence of the external stress environment, the long-term changes of the above pathways triggered a vicious circle of gradual damage to yeast cells, which is the main cause of yeast autolysis. These results may provide important clues for the in-depth interpretation of the yeast autolytic mechanism.

Regulatory network established by transcription factors transmits drought stress signals in plant.

Plants are sessile organisms that evolve with a flexible signal transduction system in order to rapidly respond to environmental changes. Drought, a common abiotic stress, affects multiple plant developmental processes especially growth. In response to drought stress, an intricate hierarchical regulatory network is established in plant to survive from the extreme environment. The transcriptional regulation carried out by transcription factors (TFs) is the most important step for the establishment of the network. In this review, we summarized almost all the TFs that have been reported to participate in drought tolerance (DT) in plant. Totally 466 TFs from 86 plant species that mostly belong to 11 families are collected here. This demonstrates that TFs in these 11 families are the main transcriptional regulators of plant DT. The regulatory network is built by direct protein-protein interaction or mutual regulation of TFs. TFs receive upstream signals possibly via post-transcriptional regulation and output signals to downstream targets via direct binding to their promoters to regulate gene expression.

Transcriptome sequencing analysis of sorghum callus with various regeneration capacities.

MAIN CONCLUSION: The possible molecular mechanisms regulating sorghum callus regeneration were revealed by RNA-sequencing. Plant callus regeneration has been widely applied in agricultural improvement. Recently, callus regeneration has been successfully applied in the genetic transformation of sorghum by using immature sorghum embryos as explants. However, the mechanism underlying callus regeneration in sorghum is still largely unknown. Here, we describe three types of callus (Callus I-III) with different redifferentiation abilities undergoing distinct induction from immature embryos of the Hiro-1 variety. Compared with nonembryonic Callus III, Callus I produced only some identifiable roots, and embryonic Callus II was sufficient to regenerate whole plants. Genome-wide transcriptome profiles were generated to reveal the underlying mechanisms. The numbers of differentially expressed genes for the three types of callus varied from 5906 to 8029. In accordance with the diverse regeneration abilities observed for different types of callus and leaf tissues, the principal component analysis revealed that the gene expression patterns of Callus I and Callus II were different from those of Callus III and leaves regenerated from Callus II. Notably, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analyses, pharmacological treatment, and substance content determinations revealed that plant ribosomes, lignin metabolic processes, and metabolism of starch and sucrose were significantly enriched, suggesting that these factors are associated with callus regeneration. These results helped elucidate the molecular regulation of three types of callus with different regeneration abilities in sorghum.

Transcriptomic analysis reveals MAPK signaling pathways affect the autolysis in baker's yeast.

Yeast autolysis refers to the process in which cells degrade and release intracellular contents under specific conditions by endogenous enzymes such as proteases, nucleases and lipid enzymes. Protein-rich baker's yeast is widely used to produce yeast extract in food industry, however, the molecular mechanism related to baker's yeast autolysis is still unclear. In this study, RNA-seq technology and biochemical analysis were performed to analyze the autolysis processes in baker's yeast. The differentially expressed genes (DEGs), 27 autolysis-related euKaryotic Ortholog Groups (KOG) and three types of autolysis-induced Gene Ontology (GO) were identified and analyzed in detail. A total of 143 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways under autolysis were also assigned. Interestingly, the DEGs were significantly enriched in the mitogen-activated protein kinase (MAPK) signaling pathways and metabolic pathways, and key genes MID2, MTL1, SLT2, PTP2, HKR1 and GPD1 may play important roles in autolysis. Further quantitative PCR was performed to verify the expression pattern in baker's yeast autolysis. Together, all these results indicated that MAPK pathways might play an essential role during autolysis process through inhibiting the metabolism and disrupting cell wall in baker's yeast. This result may provide important clues for the in-depth interpretation of the yeast autolysis mechanism.

Genome-Wide Analysis of Abscisic Acid Biosynthesis, Catabolism, and Signaling in Sorghum Bicolor under Saline-Alkali Stress.

Sorghum (Sorghum bicolor) is the fifth most important cereal crop in the world. It is an annual C4 crop due to its high biomass and wide usage, and has a strong resistance to stress. Obviously, there are many benefits of planting sorghum on marginal soils such as saline-alkali land. Although it is known that abscisic acid (ABA) is involved in plant abiotic stress responses, there are few reports on sorghum. Here, we obtained RNA-seq data, which showed gene expression at the genome-wide level under saline-alkali stress. The genes related to ABA biosynthesis, catabolism, and signaling were identified and analyzed. Meanwhile, their amino acid sequences were intermingled with rice genes to form several distinct orthologous and paralogous groups. ABA-related differentially expressed genes under saline-alkali stress were identified, and family members involved in ABA signaling were hypothesized based on the expression levels and homologous genes in rice. Furthermore, the ABA signaling pathway in Sorghum bicolor was understood better by interaction analysis. These findings present a comprehensive overview of the genes regulating ABA biosynthesis, catabolism, and signaling in Sorghum bicolor under saline-alkali stress, and provide a foundation for future research regarding their biological roles in sorghum stress tolerance.

Comparative transcriptome analysis highlights the hormone effects on somatic embryogenesis in Catalpa bungei.

KEY MESSAGE: The major pathways and key events related to somatic embryo development in Catalpa bungei were illustrated by deep analysis of DEGs and quantification of hormone contents. Catalpa bungei C.A. Meyer is a valuable timber species, known as "The king of wood" in China. Due to the low propagation rate, somatic embryogenesis-based rapid propagation can regenerate a large number of new plants in a very short period of time and thus has great commercial value for this timber species. However, the mechanisms of somatic embryogenesis in C. bungei remain largely unclear so far. In our previous study, we established the vegetative propagation system in C. bungei using immature zygotic embryo as explants. Here, we further compared the transcriptional profiles and hormones contents between the embryogenic callus (EC) and non-embryogenic callus (NEC). RNA-seq analysis showed a total assembly of 73038 unigenes, and identified 12310 differentially expressed genes (DEGs) between EC and NEC. Also, six DEGs were chosen to verify the authenticity of the transcriptome sequencing results by qRT-PCR. Moreover, by using LC-MS approaches, we quantified various plant hormone contents and found that auxin and ABA were dramatically higher in EC than those in NEC. Accordingly, DEGs were enriched in plant hormone signaling pathways. Taken together, we highlight the hormone effects on somatic embryogenesis in a tree species, C. bungei. The use of certain genes as markers of embryogenesis induction in C. bungei regeneration process will provide new tools to pre-screen genotypes or tissue culture hormone combinations suitable for somatic embryo production. Our results provide theoretical references for the somatic embryogenesis mechanism and experimental bases for breeding and rapid propagation of C. bungei.

Isolation and Functional Analysis of PISTILLATA Homolog From Magnolia wufengensis.

PISTILLATA (PI) homologs are crucial regulators of flower development in angiosperms. In this study, we isolated the MAwuPI homolog from Magnolia wufengensis, a basal angiosperm belonging to the Magnoliaceae. Molecular phylogenetic analysis suggested that MAwuPI was grouped into the PI/GLO lineages of B-class MADS-box gene with the distinctive PI motif. Further expression profiling analysis showed that MAwuPI was expressed in tepals and stamens but not in juvenile leaves and carpels, similar to the spatial expression pattern of AtPI in Arabidopsis. Interestingly, MAwuPI had higher expression level in inner-tepals than in outer-tepals, whereas the M. wufengensis flower is homochlamydeous. Moreover, ectopic expression of MAwuPI in Arabidopsis pi-1 mutant emerged filament-like structures but had no obvious petals, suggesting a partial phenotypic recovery of pi-1 mutant. The features of MAwuPI in the expression pattern and gene function improved our acknowledgment of B-class genes in M. wufengensis, and contributed to the clarification of M. wufengensis evolution status and relations with other sibling species in molecular perspective.

Isolation and Characterization of AGAMOUS-Like Genes Associated With Double-Flower Morphogenesis in Kerria japonica (Rosaceae).

Double-flower phenotype is more popular and attractive in garden and ornamental plants. There is great interest in exploring the molecular mechanisms underlying the double-flower formation for further breeding and selection. Kerria japonica, a commercial ornamental shrub of the Rosaceae family, is considered an excellent system to determine the mechanisms of morphological alterations, because it naturally has a single-flower form and double-flower variant with homeotic conversion of stamens into petals and carpels into leaf-like carpels. In this study, Sf-KjAG (AGAMOUS homolog of single-flower K. japonica) and Df-KjAG (AGAMOUS homolog of double-flower K. japonica) were isolated and characterized as two AGAMOUS (AG) homologs that occur strictly in single- and double-flower K. japonica, respectively. Our sequence comparison showed that Df-KjAG is derived from ectopic splicing with the insertion of a 2411 bp transposon-like fragment, which might disrupt mRNA accumulation and protein function, into intron 1. Ectopic expression analysis in Arabidopsis revealed that Sf-KjAG is highly conserved in specifying carpel and stamen identities. However, Df-KjAG did not show any putative C-class function in floral development. Moreover, yeast-two-hybrid assays showed that Sf-KjAG can interact with KjAGL2, KjAGL9, and KjAP1, whereas Df-KjAG has lost interactions with these floral identity genes. In addition, loss-of-function of Df-KjAG affected not only its own expression, but also that of other putative floral organ identity genes such as KjAGL2, KjAGL9, KjAP1, KjAP2, KjAP3, and KjPI. In conclusion, our findings suggest that double-flower formation in K. japonica can be attributed to Df-KjAG, which appears to be a mutant produced by the insertion of a transposon-like fragment in the normal AG homolog (Sf-KjAG) of single-flower K. japonica. Highlights:Sf-KjAG and Df-KjAG are different variations only distinguished by a transposon-like fragment insertion which lead to the evolutionary transformation from single-flower to double-flowers morphogenesis in Kerria japonica.

SlMYB12 Regulates Flavonol Synthesis in Three Different Cherry Tomato Varieties.

Cherry tomato (Lycopersicon esculentum M.) is considered a healthy fruit worldwide due to its wide range of nutrients. Flavonol, one of the major nutrients in cherry tomato, has antioxidant and cell-modulating properties. In this study, we showed a correlation between the expression of SlMYB12 and flavonol content (R2 = 0.922). To characterize the function of SlMYB12, SlMYB12-overexpressing transgenic tomato plants were generated in three different cherry tomato varieties. Significant increases in flavonol content and flavonol biosynthetic gene expression were identified in SlMYB12-overexpressing plants. Therefore, we suggest that SlMYB12 plays a positive role in the flavonol biosynthesis pathway in cherry tomatoes, which further indicates a potential role as a marker in analyzing flavonol content in different cherry tomato varieties.

Floral organ MADS-box genes in Cercidiphyllum japonicum (Cercidiphyllaceae): Implications for systematic evolution and bracts definition.

The dioecious relic Cercidiphyllum japonicum is one of two species of the sole genus Cercidiphyllum, with a tight inflorescence lacking an apparent perianth structure. In addition, its systematic place has been much debated and, so far researches have mainly focused on its morphology and chloroplast genes. In our investigation, we identified 10 floral organ identity genes, including four A-class, three B-class, two C-class and one D-class. Phylogenetic analyses showed that all ten genes are grouped with Saxifragales plants, which confirmed the phylogenetic place of C. japonicum. Expression patterns of those genes were examined by quantitative reverse transcriptase PCR, with some variations that did not completely coincide with the ABCDE model, suggesting some subfunctionalization. As well, our research supported the idea that thebract actually is perianth according to our morphological and molecular analyses in Cercidiphyllum japonicum.

Development of Marker-Free Transgenic Potato Tubers Enriched in Caffeoylquinic Acids and Flavonols.

Potato (Solanum tuberosum L.) is a major crop worldwide that meets human economic and nutritional requirements. Potato has several advantages over other crops: easy to cultivate and store, cheap to consume, and rich in a variety of secondary metabolites. In this study, we generated three marker-free transgenic potato lines that expressed the Arabidopsis thaliana flavonol-specific transcriptional activator AtMYB12 driven by the tuber-specific promoter Patatin. Marker-free potato tubers displayed increased amounts of caffeoylquinic acids (CQAs) (3.35-fold increases on average) and flavonols (4.50-fold increase on average). Concentrations of these metabolites were associated with the enhanced expression of genes in the CQA and flavonol biosynthesis pathways. Accumulation of CQAs and flavonols resulted in 2-fold higher antioxidant capacity compared to wild-type potatoes. Tubers from these marker-free transgenic potatoes have therefore improved antioxidant properties.

Genome-wide analysis reveals divergent patterns of gene expression during zygotic and somatic embryo maturation of Theobroma cacao L., the chocolate tree.

BACKGROUND: Theobroma cacao L. is a tropical fruit tree, the seeds of which are used to create chocolate. In vitro somatic embryogenesis (SE) of cacao is a propagation system useful for rapid mass-multiplication to accelerate breeding programs and to provide plants directly to farmers. Two major limitations of cacao SE remain: the efficiency of embryo production is highly genotype dependent and the lack of full cotyledon development results in low embryo to plant conversion rates. With the goal to better understand SE development and to improve the efficiency of SE conversion we examined gene expression differences between zygotic and somatic embryos using a whole genome microarray. RESULTS: The expression of 28,752 genes was determined at 4 developmental time points during zygotic embryogenesis (ZE) and 2 time points during cacao somatic embryogenesis (SE). Within the ZE time course, 10,288 differentially expressed genes were enriched for functions related to responses to abiotic and biotic stimulus, metabolic and cellular processes. A comparison ZE and SE expression profiles identified 10,175 differentially expressed genes. Many TF genes, putatively involved in ethylene metabolism and response, were more strongly expressed in SEs as compared to ZEs. Expression levels of genes involved in fatty acid metabolism, flavonoid biosynthesis and seed storage protein genes were also differentially expressed in the two types of embryos. CONCLUSIONS: Large numbers of genes were differentially regulated during various stages of both ZE and SE development in cacao. The relatively higher expression of ethylene and flavonoid related genes during SE suggests that the developing tissues may be experiencing high levels of stress during SE maturation caused by the in vitro environment. The expression of genes involved in the synthesis of auxin, polyunsaturated fatty acids and secondary metabolites was higher in SEs relative to ZEs despite lack of lipid and metabolite accumulation. These differences in gene transcript levels associated with critical processes during seed development are consistent with the fact that somatic embryos do not fully develop the large storage cotyledons found in zygotic embryos. These results provide insight towards design of improved protocols for cacao somatic embryogenesis.

Conversion of tryptophan to indole-3-acetic acid by TRYPTOPHAN AMINOTRANSFERASES OF ARABIDOPSIS and YUCCAs in Arabidopsis.

Auxin is an essential hormone, but its biosynthetic routes in plants have not been fully defined. In this paper, we show that the TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) family of amino transferases converts tryptophan to indole-3-pyruvate (IPA) and that the YUCCA (YUC) family of flavin monooxygenases participates in converting IPA to indole-3-acetic acid, the main auxin in plants. Both the YUCs and the TAAs have been shown to play essential roles in auxin biosynthesis, but it has been suggested that they participate in two independent pathways. Here, we show that all of the taa mutant phenotypes, including defects in shade avoidance, root resistance to ethylene and N-1-naphthylphthalamic acid (NPA), are phenocopied by inactivating YUC genes. On the other hand, we show that the taa mutants in several known auxin mutant backgrounds, including pid and npy1, mimic all of the well-characterized developmental defects caused by combining yuc mutants with the auxin mutants. Furthermore, we show that overexpression of YUC1 partially suppresses the shade avoidance defects of taa1 and the sterile phenotypes of the weak but not the strong taa mutants. In addition, we discovered that the auxin overproduction phenotypes of YUC overexpression lines are dependent on active TAA genes. Our genetic data show that YUC and TAA work in the same pathway and that YUC is downstream of TAA. The yuc mutants accumulate IPA, and the taa mutants are partially IPA-deficient, indicating that TAAs are responsible for converting tryptophan to IPA, whereas YUCs play an important role in converting IPA to indole-3-acetic acid.

OsEDR1 negatively regulates rice bacterial resistance via activation of ethylene biosynthesis.

Rice OsEDR1 is a sequence ortholog of Arabidopsis EDR1. However, its molecular function is unknown. We show here that OsEDR1-suppressing/knockout (KO) plants, which developed spontaneous lesions on the leaves, have enhanced resistance to Xanthomonas oryzae pv. oryzae (Xoo) causing bacterial blight disease. This resistance was associated with increased accumulation of salicylic acid (SA) and jasmonic acid (JA), induced expression of SA- and JA-related genes and suppressed accumulation of 1-aminocyclopropane-1-carboxylic acid (ACC), the direct precursor of ethylene, and expression of ethylene-related genes. OsEDR1-KO plants also showed suppressed production of ethylene. Knockout of OsEDR1 suppressed the ACC synthase (ACS) gene family, which encodes the rate-limiting enzymes of ethylene biosynthesis by catalysing the formation of ACC. The lesion phenotype and enhanced bacterial resistance of the OsEDR1-KO plants was partly complemented by the treatment with ACC. ACC treatment was associated with decreased SA and JA biosynthesis in OsEDR1-KO plants. In contrast, aminoethoxyvinylglycine, the inhibitor of ethylene biosynthesis, promoted expression of SA and JA synthesis-related genes in OsEDR1-KO plants. These results suggest that ethylene is a negative signalling molecule in rice bacterial resistance. In the rice-Xoo interaction, OsEDR1 transcriptionally promotes the synthesis of ethylene that, in turn, suppresses SA- and JA-associated defence signalling.

Opposite functions of a rice mitogen-activated protein kinase during the process of resistance against Xanthomonas oryzae.

The pathogen-induced plant defense signaling network consists of multiple components, although only some of them are characterized. Most of the known components function either as activators or repressors in host-pathogen interactions. Here we report that a mitogen-activated protein kinase, OsMPK6, functions both as an activator and a repressor in rice resistance against Xanthomonas oryzae pv. oryzae (Xoo), the causal organism of bacterial blight disease. Activation of OsMPK6 resulted in the formation of lesion mimics and local resistance to Xoo, accompanied by the accumulation of salicylic acid (SA) and jasmonic acid (JA), and the induced expression of SA- and JA-signaling genes. Nuclear localization of OsMPK6 was essential for local resistance, suggesting that modulating the expression of defense-responsive genes through transcription regulators may be the primary mechanism of OsMPK6-mediated local resistance. The knock-out of OsMPK6 resulted in enhanced Xoo resistance, increased accumulation of SA and enhanced resistance to X. oryzae pv. oryzicola, the causal organism of bacterial streak disease, in systemic tissues. Xoo infection induced the expression of PR1a, the marker gene of systemic acquired resistance (SAR), in systemic health tissues of OsMPK6-knock-out plants. These results suggest that OsMPK6 negatively regulates SAR. Thus OsMPK6 is a two-faced player in the rice-Xoo interaction.