Chaojie Xie

Diverse set of microRNAs are responsive to powdery mildew infection and heat stress in wheat (Triticum aestivum L.)

BackgroundMicroRNAs (miRNAs) are a class of small non-coding regulatory RNAs that regulate gene expression by guiding target mRNA cleavage or translational inhibition. MiRNAs can have large-scale regulatory effects on development and stress response in plants.ResultsTo test whether miRNAs play roles in regulating response to powdery mildew infection and heat stress in wheat, by using Solexa high-throughput sequencing we cloned the small RNA from wheat leaves infected by preponderant physiological strain Erysiphe graminis f. sp. tritici (Egt) or by heat stress treatment. A total of 153 miRNAs were identified, which belong to 51 known and 81 novel miRNA families. We found that 24 and 12 miRNAs were responsive to powdery mildew infection and heat stress, respectively. We further predicted that 149 target genes were potentially regulated by the novel wheat miRNA.ConclusionsOur results indicated that diverse set of wheat miRNAs were responsive to powdery mildew infection and heat stress and could function in wheat responses to both biotic and abiotic stresses.

Identification and characterization of wheat long non-protein coding RNAs responsive to powdery mildew infection and heat stress by using microarray analysis and SBS sequencing

BackgroundBiotic and abiotic stresses, such as powdery mildew infection and high temperature, are important limiting factors for yield and grain quality in wheat production. Emerging evidences suggest that long non-protein coding RNAs (npcRNAs) are developmentally regulated and play roles in development and stress responses of plants. However, identification of long npcRNAs is limited to a few plant species, such as Arabidopsis, rice and maize, no systematic identification of long npcRNAs and their responses to abiotic and biotic stresses is reported in wheat.ResultsIn this study, by using computational analysis and experimental approach we identified 125 putative wheat stress responsive long npcRNAs, which are not conserved among plant species. Among them, some were precursors of small RNAs such as microRNAs and siRNAs, two long npcRNAs were identified as signal recognition particle (SRP) 7S RNA variants, and three were characterized as U3 snoRNAs. We found that wheat long npcRNAs showed tissue dependent expression patterns and were responsive to powdery mildew infection and heat stress.ConclusionOur results indicated that diverse sets of wheat long npcRNAs were responsive to powdery mildew infection and heat stress, and could function in wheat responses to both biotic and abiotic stresses, which provided a starting point to understand their functions and regulatory mechanisms in the future.

Molecular identification of a new powdery mildew resistance gene Pm41 on chromosome 3BL derived from wild emmer (Triticum turgidum var. dicoccoides).

Powdery mildew caused by Blumeria graminis f. sp. tritici is an important wheat disease in China and other parts of the world. Wild emmer (Triticum turgidum var. dicoccoides) is the immediate progenitor of cultivated tetraploid and hexaploid wheats and thus an important resource for wheat improvement. Wild emmer accession IW2 collected from Mount Hermon, Israel, is highly resistant to powdery mildew at the seedling and adult plant stages. Genetic analysis using an F2 segregating population and F2:3 families, derived from a cross between susceptible durum cultivar Langdon and wild emmer accession IW2, indicated that a single dominant gene was responsible for the resistance of IW2. Bulked segregant and molecular marker analyses detected that six polymorphic SSR, one ISBP, and three EST-STS markers on chromosome 3BL bin 0.63–1.00 were linked to the resistance gene. Allelic variations of resistance-linked EST-STS marker BE489472 revealed that the allele was present only in wild emmer but absent in common wheat. Segregation distortion was observed for the powdery mildew resistance allele and its linked SSR markers with preferential transmission of Langdon alleles over IW2 alleles. The resistance gene was introgressed into common wheat by backcrossing and marker-assisted selection. Since no designated powdery mildew resistance gene has been found on chromosome 3BL, the resistance gene derived from wild emmer accession IW2 appears to be new one and was consequently designated Pm41.

Identification and genetic mapping of a powdery mildew resistance gene in wild emmer (Triticum dicoccoides) accession IW72 from Israel

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a devastating disease of wheat (Triticum aestivum) in China and worldwide, causing severe yield losses annually. Wild emmer (T. dicoccoides) accession IW72 collected from Israel is resistant to powdery mildew at the seedling and adult stages. Genetic analysis indicated that the resistance was controlled by a single dominant gene, temporarily designated MlIW72. The F2 population and F3 families derived from a hybrid between IW72 and susceptible durum wheat line Mo75 were used for molecular mapping of the resistance gene. MlIW72 was linked with SSR loci Xgwm344, Xcfa2040, Xcfa2240, Xcfa2257 and Xwmc525 on the long arm of chromosome 7A. In addition, two STS markers, MAG2185 (derived from RFLP marker PSR680) and MAG1759 (developed from EST CD452874), were mapped close to MlIW72. All these markers were physically located in the terminal bin 0.86–1.00 of 7AL. The chromosome location and genetic mapping results suggested that the powdery mildew resistance gene identified in wild emmer accession IW72 might be a new allele at the Pm1 locus or a new locus closely linked to Pm1.

Transcriptome comparison of susceptible and resistant wheat in response to powdery mildew infection.

Powdery mildew (Pm) caused by the infection of Blumeria graminis f. sp. tritici (Bgt) is a worldwide crop disease resulting in significant loss of wheat yield. To profile the genes and pathways responding to the Bgt infection, here, using Affymetrix wheat microarrays, we compared the leaf transcriptomes before and after Bgt inoculation in two wheat genotypes, a Pm-susceptible cultivar Jingdong 8 (S) and its near-isogenic line (R) carrying a single Pm resistant gene Pm30. Our analysis showed that the original gene expression status in the S and R genotypes of wheat was almost identical before Bgt inoculation, since only 60 genes exhibited differential expression by P = 0.01 cutoff. However, 12 h after Bgt inoculation, 3014 and 2800 genes in the S and R genotype, respectively, responded to infection. A wide range of pathways were involved, including cell wall fortification, flavonoid biosynthesis and metabolic processes. Furthermore, for the first time, we show that sense-antisense pair genes might be participants in wheat-powdery mildew interaction. In addition, the results of qRT-PCR analysis on several candidate genes were consistent with the microarray data in their expression patterns. In summary, this study reveals leaf transcriptome changes before and after powdery mildew infection in wheat near-isogenic lines, suggesting that powdery mildew resistance is a highly complex systematic response involving a large amount of gene regulation.

A “one-marker-for-two-genes” approach for efficient molecular discrimination of Pm12 and Pm21 conferring resistance to powdery mildew in wheat

Powdery mildew, caused by Blumeria graminis f. sp. tritici, is one of the most important wheat diseases worldwide. Pyramiding different resistance genes into single cultivar has been proposed as one remedy to provide durable resistance. Powdery mildew resistance genes Pm12 (T6BS-6SS.6SL), transferred from Aegilops speltoides to wheat cv. Wembley, and Pm21 (T6VS.6AL), introduced from Dasypyrum villosum to wheat cv. Yangmai5, conferred broad-spectrum resistance to B. graminis f. sp. tritici. Both Pm12 and Pm21 genes are located on the short arms of homologous group six involved translocated chromosomes 6SS.6BL and 6VS.6AL, respectively. Simple sequence repeat motifs of wheat simple sequence repeat (SSR) and expressed sequence tag (EST) sequences on the short arm of homologous group six chromosomes were analyzed to develop molecular markers for discriminating chromosome arms 6AS, 6BS, 6DS, 6VS, and 6SS. One EST–SSR marker, Xcau127, was polymorphic, and therefore can be used to distinguish the two resistance genes and the respective susceptible alleles. This marker allowed us to develop an efficient “one-marker-for-two-genes” procedure for identifying powdery mildew resistance genes Pm12 and Pm21 for marker-assisted selection and gene pyramiding in wheat breeding programs.

Molecular Mapping and Chromosomal Location of Powdery Mildew Resistance Gene in Wheat Cultivar Tangmai 4

Abstract Powdery mildew, caused by Blumeria graminis f. sp. tritici , is one of the most important diseases in wheat ( Triticum aestivum L.) worldwide. Breeding for resistance is the most economical and effective method for controlling the disease. Tangmai 4 carries a pair of T1BL·1RS wheat-rye ( Secale cereale L.) translocated chromosomes and is resistant to a wide spectrum of wheat powdery mildew isolates. Genetic analysis indicated that a single semidominant gene in Tangmai 4 conferred resistance to powdery mildew, temporarily designated PmTm4 . Segregating F 2 population and their F 3 progenies derived from the cross between Tangmai 4 and Clement were used for bulked segregation analysis. Four SSR, one EST-SSR, and one EST-STS polymorphic markers were linked to the powdery mildew resistance gene PmTm4 in an order of Xcau12–Xgwm611–PmTm4–XEST92–Xbarc1073–Xbarc82 . Gene PmTm4 was physically mapped on the distal bin of chromosome 7BL using Chinese Spring nullisomic-tetrasomic, ditelosomic, and deletion lines. The results demonstrate that PmTm4 gene may be either an allele at the Pm5 locus or a member of closely linked cluster of genes.

Overexpression of a wheat stearoyl-ACP desaturase (SACPD) gene TaSSI2 in Arabidopsis ssi2 mutant compromise its resistance to powdery mildew

Fatty acids and their derivatives play important roles in plant defense responses. It has been shown that a mutation in a gene encoding one of stearoyl acyl carrier protein fatty acid desaturase isoforms (ssi2 mutant) enhances the resistance of Arabidopsis to multiple pathogens, and similar results were obtained in rice and soybean. However, it is unknown whether the ssi2 mutant is also resistant to powdery mildew (Golovinomyces cichoracearum). In this study, the ssi2 mutant showed enhanced resistance to powdery mildew. Furthermore, we described the cloning and characterization of the TaSSI2 gene (ortholog of AtSSI2) from wheat. Functional analysis of TaSSI2 was performed by overexpressing TaSSI2 in ssi2 mutant of Arabidopsis. The result indicated that ectopic expression of TaSSI2 restored the WT like morphology in the ssi2 background, the 35S:TaSSI2/ssi2 plants accumulated WT-like levels of oleic acid (18:1) and the transcript levels of R genes were significantly lower than that in ssi2 plants. In contrast to the constitutive PR gene expression in ssi2 plants, the transcript accumulation of PR1 and PR2 was similar in the 35S:TaSSI2/ssi2 and wild type both before and after inoculation. Trypan blue staining showed that extensive fungal hyphae and conidiophores were produced in wild-type and 35S:TaSSI2/ssi2 leaves while no visible powdery mildew growth was observed, but dramatic lesions developed at the infection sites in the ssi2 mutant leaves. Our results demonstrated that TaSSI2 is involved in the negative regulation of defense responses in powdery mildew infection, similar to its counterparts in Arabidopsis, indicating a highly conserved function of SSI2 gene in diverse plants.

A novel histidine kinase gene, ZmHK9, mediate drought tolerance through the regulation of stomatal development in Arabidopsis.

Plants have developed complex signaling networks to regulate biochemical and physiological acclimation, environmental signals were perceived and transmitted to cellular machinery to activate adaptive responses. Here, a novel drought responsive histidine kinase gene was identified and designated as ZmHK9. Under normal conditions, ZmHK9 was predominantly expressed in roots, and the roots of ZmHK9-OX transgenic lines are markedly hypersensitive to ABA and ethylene, as compare to wild type. Consistent with its expression induced by PEG and exogenous ABA treatment, promoter sequence of this gene possessed drought and ABA responsive element. Moreover, the transgenic plants were much less affected by drought stress and recovered quickly after rewatering, stomatal complex size and stomatal density in the transgenic plants are significantly smaller and lower than those of the wild-type plants. In addition, ABA induced stomatal closure and the stomatal aperture of ZmHK9-OX lines was smaller than that of wild type. Collectively, it can be concluded that ZmHK9 regulates root elongation, stomatal development and drought tolerance through ABA dependent signaling pathway in Arabidopsis.

Differential effects of a post-anthesis heat stress on wheat ( Triticum aestivum L.) grain proteome determined by iTRAQ

Heat stress, a major abiotic stressor of wheat (Triticum aestivum L.), often results in reduced yield and decreased quality. In this study, a proteomic method, Tags for Relative and Absolute Quantitation Isobaric (iTRAQ), was adopted to analyze the protein expression profile changes among wheat cultivar Jing411 under heat stress. Results indicated that there were 256 different proteins expressed in Jing411 under heat stress. According to the result of gene annotation and functional classification, 239 proteins were annotated by 856 GO function entries, including growth and metabolism proteins, energy metabolism proteins, processing and storage proteins, defense-related proteins, signal transduction, unknown function proteins and hypothetical proteins. GO enrichment analysis suggested that the differentially expressed proteins in Jing411 under heat stress were mainly involved in stimulus response (67), abiotic stress response (26) and stress response (58), kinase activity (12), and transferase activity (12). Among the differentially expressed proteins in Jing411, 115 were attributed to 119 KEGG signaling/metabolic pathways. KEGG pathway enrichment analysis in Jing411 showed that heat stress mainly affected the starch and sucrose metabolism as well as protein synthesis pathway in the endoplasmic reticulum. The protein interaction network indicated that there were 8 differentially expressed proteins that could form an interaction network in Jing411.