Hai Peng

Expansion and stress responses of AP2/EREBP superfamily in Brachypodium Distachyon

APETALA2/ethylene-responsive element binding protein (AP2/EREBP) transcription factors constitute one of the largest and most conserved gene families in plant, and play essential roles in growth, development and stress response. Except a few members, the AP2/EREBP family has not been characterized in Brachypodium distachyon, a model plant of Poaceae. We performed a genome-wide study of this family in B. distachyon by phylogenetic analyses, transactivation assays and transcript profiling. A total of 149 AP2/EREBP genes were identified and divided into four subfamilies, i.e., ERF (ethylene responsive factor), DREB (dehydration responsive element binding gene), RAV (related to ABI3/VP) and AP2. Tandem duplication was a major force in expanding B. distachyon AP2/EREBP (BdAP2/EREBP) family. Despite a significant expansion, genomic organizations of BdAP2/EREBPs were monotonous as the majority of them, except those of AP2 subfamily, had no intron. An analysis of transcription activities of several closely related and duplicated BdDREB genes showed their functional divergence and redundancy in evolution. The expression of BdAP2/EREBPs in different tissues and the expression of DREB/ERF subfamilies in B. distachyon, wheat and rice under abiotic stresses were investigated by next-generation sequencing and microarray profiling. Our results are valuable for further function analysis of stress tolerant AP2/EREBP genes in B. distachyon.

Chilling acclimation provides immunity to stress by altering regulatory networks and inducing genes with protective functions in Cassava

BackgroundStress acclimation is an effective mechanism that plants acquired for adaption to dynamic environment. Even though generally considered to be sensitive to low temperature, Cassava, a major tropical crop, can be tolerant to much lower temperature after chilling acclimation. Improvement to chilling resistance could be beneficial to breeding. However, the underlying mechanism and the effects of chilling acclimation on chilling tolerance remain largely unexplored.ResultsIn order to understand the mechanism of chilling acclimation, we profiled and analyzed the transcriptome and microRNAome of Cassava, using high-throughput deep sequencing, across the normal condition, a moderate chilling stress (14°C), a harsh stress (4°C) after chilling acclimation (14°C), and a chilling shock from 24°C to 4°C. The results revealed that moderate stress and chilling shock triggered comparable degrees of transcriptional perturbation, and more importantly, about two thirds of differentially expressed genes reversed their expression from up-regulation to down-regulation or vice versa in response to hash stress after experiencing moderate stress. In addition, microRNAs played important roles in the process of this massive genetic circuitry rewiring. Furthermore, function analysis revealed that chilling acclimation helped the plant develop immunity to further harsh stress by exclusively inducing genes with function for nutrient reservation therefore providing protection, whereas chilling shock induced genes with function for viral reproduction therefore causing damage.ConclusionsOur study revealed, for the first time, the molecular basis of chilling acclimation, and showed potential regulation role of microRNA in chilling response and acclimation in Euphorbia.

Endogenous small-noncoding RNAs and their roles in chilling response and stress acclimation in Cassava.

BackgroundSmall noncoding RNA (sncRNA), including microRNAs (miRNAs) and endogenous small-interfering RNAs (endo-siRNAs) are key gene regulators in eukaryotes, playing critical roles in plant development and stress tolerance. Trans-acting siRNAs (ta-siRNAs), which are secondary siRNAs triggered by miRNAs, and siRNAs from natural antisense transcripts (nat-siRNAs) are two well-studied classes of endo-siRNAs.ResultsIn order to understand sncRNAs’ roles in plant chilling response and stress acclimation, we performed a comprehensive study of miRNAs and endo-siRNAs in Cassava (Manihot esculenta), a major source of food for the world populations in tropical regions. Combining Next-Generation sequencing and computational and experimental analyses, we profiled and characterized sncRNA species and mRNA genes from the plants that experienced severe and moderate chilling stresses, that underwent further severe chilling stress after chilling acclimation at moderate stress, and that grew under the normal condition. We also included castor bean (Ricinus communis) in our study to understand conservation of sncRNAs. In addition to known miRNAs, we identified 32 (22 and 10) novel miRNAs as well as 47 (26 and 21) putative secondary siRNA-yielding and 8 (7 and 1) nat-siRNA-yielding candidate loci in Cassava and castor bean, respectively. Among the expressed sncRNAs, 114 miRNAs, 12 ta-siRNAs and 2 nat-siRNAs showed significant expression changes under chilling stresses.ConclusionSystematic and computational analysis of microRNAome and experimental validation collectively showed that miRNAs, ta-siRNAs, and possibly nat-siRNAs play important roles in chilling response and chilling acclimation in Cassava by regulating stress-related pathways, e.g. Auxin signal transduction. The conservation of these sncRNA might shed lights on the role of sncRNA-mediated pathways affected by chilling stress and stress acclimation in Euphorbiaceous plants.

Comprehensive Definition of Genome Features in Spirodela polyrhiza by High-Depth Physical Mapping and Short-Read DNA Sequencing Strategies

&NA; Spirodela polyrhiza is a fast‐growing aquatic monocot with highly reduced morphology, genome size and number of protein‐coding genes. Considering these biological features of Spirodela and its basal position in the monocot lineage, understanding its genome architecture could shed light on plant adaptation and genome evolution. Like many draft genomes, however, the 158‐Mb Spirodela genome sequence has not been resolved to chromosomes, and important genome characteristics have not been defined. Here we deployed rapid genome‐wide physical maps combined with high‐coverage short‐read sequencing to resolve the 20 chromosomes of Spirodela and to empirically delineate its genome features. Our data revealed a dramatic reduction in the number of the rDNA repeat units in Spirodela to fewer than 100, which is even fewer than that reported for yeast. Consistent with its unique phylogenetic position, small RNA sequencing revealed 29 Spirodela‐specific microRNA, with only two being shared with Elaeis guineensis (oil palm) and Musa balbisiana (banana). Combining DNA methylation data and small RNA sequencing enabled the accurate prediction of 20.5% long terminal repeats (LTRs) that doubled the previous estimate, and revealed a high Solo:Intact LTR ratio of 8.2. Interestingly, we found that Spirodela has the lowest global DNA methylation levels (9%) of any plant species tested. Taken together our results reveal a genome that has undergone reduction, likely through eliminating non‐essential protein coding genes, rDNA and LTRs. In addition to delineating the genome features of this unique plant, the methodologies described and large‐scale genome resources from this work will enable future evolutionary and functional studies of this basal monocot family. Significance statement Spirodela polyrhiza is a fast‐growing aquatic and basal monocot with a small genome, so understanding its genome architecture should inform plant adaptation strategies and genome evolution. However, long repetitive regions are formidable challenges for the proper assembly, annotation and closure of genome projects. Here we overcame this bottleneck by combining high‐throughput sequencing and genome mapping technologies to generate a validated sequence map of the 20 Spirodela polyrhiza chromosomes. Genome‐wide profiling data revealed a genome in a cycle of reduction with very low global DNA methylation and a reduced ribosomal DNA as well as gene content.

Rice Xa21 primed genes and pathways that are critical for combating bacterial blight infection

Rice bacterial blight (BB) is a devastating rice disease. The Xa21 gene confers a broad and persistent resistance against BB. We introduced Xa21 into Oryza sativa L ssp indica (rice 9311), through multi-generation backcrossing, and generated a nearly isogenic, blight-resistant 9311/Xa21 rice. Using next-generation sequencing, we profiled the transcriptomes of both varieties before and within four days after infection of bacterium Xanthomonas oryzae pv. oryzae. The identified differentially expressed (DE) genes and signaling pathways revealed insights into the functions of Xa21. Surprisingly, before infection 1,889 genes on 135 of the 316 signaling pathways were DE between the 9311/Xa21 and 9311 plants. These Xa21-mediated basal pathways included mainly those related to the basic material and energy metabolisms and many related to phytohormones such as cytokinin, suggesting that Xa21 triggered redistribution of energy, phytohormones and resources among essential cellular activities before invasion. Counter-intuitively, after infection, the DE genes between the two plants were only one third of that before the infection; other than a few stress-related pathways, the affected pathways after infection constituted a small subset of the Xa21-mediated basal pathways. These results suggested that Xa21 primed critically important genes and signaling pathways, enhancing its resistance against bacterial infection.

DNA methylation polymorphism and stability in Chinese indica hybrid rice

Conventional rice breeding has long focused on exploiting the DNA sequence diversity. However, epigenetic diversity, reflected particularly in DNA methylation, can also contribute to phenotypic variation and should not be overlooked in rice breeding. In this study, 20 parental lines of indica rice, which are widely used in hybrid rice breeding in China, were analyzed to investigate variations of DNA methylation and its inheritance. The results revealed a wide diversity in DNA methylation among these breeding lines. A positive correlation was seen between DNA methylation and genetic diversity. Furthermore, some of the methylated DNA was inherited in the subsequent generation, regardless of whether they were produced by selfing or hybrid-crossing. This study provides insight into the methylation patterns in rice, and suggests the importance of epigenetic diversity in rice breeding.

An accurate and efficient method for large-scale SSR genotyping and applications

Abstract Accurate and efficient genotyping of simple sequence repeats (SSRs) constitutes the basis of SSRs as an effective genetic marker with various applications. However, the existing methods for SSR genotyping suffer from low sensitivity, low accuracy, low efficiency and high cost. In order to fully exploit the potential of SSRs as genetic marker, we developed a novel method for SSR genotyping, named as AmpSeq-SSR, which combines multiplexing polymerase chain reaction (PCR), targeted deep sequencing and comprehensive analysis. AmpSeq-SSR is able to genotype potentially more than a million SSRs at once using the current sequencing techniques. In the current study, we simultaneously genotyped 3105 SSRs in eight rice varieties, which were further validated experimentally. The results showed that the accuracies of AmpSeq-SSR were nearly 100 and 94% with a single base resolution for homozygous and heterozygous samples, respectively. To demonstrate the power of AmpSeq-SSR, we adopted it in two applications. The first was to construct discriminative fingerprints of the rice varieties using 3105 SSRs, which offer much greater discriminative power than the 48 SSRs commonly used for rice. The second was to map Xa21, a gene that confers persistent resistance to rice bacterial blight. We demonstrated that genome-scale fingerprints of an organism can be efficiently constructed and candidate genes, such as Xa21 in rice, can be accurately and efficiently mapped using an innovative strategy consisting of multiplexing PCR, targeted sequencing and computational analysis. While the work we present focused on rice, AmpSeq-SSR can be readily extended to animals and micro-organisms.

New class of transcription factors controls flagellar assembly by recruiting RNA polymerase II in Chlamydomonas

Significance Transcriptional regulation of flagellar genes controls an initial step in flagellar assembly. In this study, we show that XAP5, a conserved protein of unknown function, defines a class of transcription factor for transcriptional regulation of genes involved in flagellar assembly. Phosphorylation of X chromosome-associated protein 5 (XAP5) during flagellar regeneration tracks flagellar length. Remarkably, recruitment of RNA polymerase II (Pol II) machinery for transcriptional activation depends on the activities of XAP5. Our data demonstrate that XAP5 functions as a transcription factor for transcriptional regulation of flagellar genes through recruitment of RNA Pol II. Our results enhance our understanding of the biochemical function of the XAP5 family and the transcriptional regulation of flagellar assembly. Cells have developed regulatory mechanisms that underlie flagellar assembly and maintenance, including the transcriptional regulation of flagellar genes, an initial step for making flagella. Although transcriptional regulation of flagellar gene expression is required for flagellar assembly in Chlamydomonas, no transcription factor that regulates the transcription of flagellar genes has been identified. We report that X chromosome-associated protein 5 (XAP5) acts as a transcription factor to regulate flagellar assembly in Chlamydomonas. While XAP5 proteins are evolutionarily conserved across diverse organisms and play vital roles in diverse biological processes, nothing is known about the biochemical function of any member of this important protein family. Our data show that loss of XAP5 leads to defects in flagellar assembly. Posttranslational modifications of XAP5 track flagellar length during flagellar assembly, suggesting that cells possess a feedback system that modulates modifications to XAP5. Notably, XAP5 regulates flagellar gene expression via directly binding to a motif containing a CTGGGGTG-core. Furthermore, recruitment of RNA polymerase II (Pol II) machinery for transcriptional activation depends on the activities of XAP5. Our data demonstrate that, through recruitment of Pol II, XAP5 defines a class of transcription factors for transcriptional regulation of ciliary genes. This work provides insights into the biochemical function of the XAP5 family and the fundamental biology of the flagellar assembly, which enhance our understanding of the signaling and functions of flagella.

Quality control of the traditional Chinese medicine Ruyi jinhuang powder based on high-throughput sequencing and real-time PCR

Traditional Chinese medicine (TCM) has been practiced for thousands of years, although concerns about the efficacy, legality, and safety of TCM continue to be raised. Chromatographic studies have detected the presence of heavy metals and plant toxins within some TCM preparations. However, chromatography is not able to identify all of the compounds of TCM, particularly those items that are not clearly labeled on the packaging. The present study aimed to establish a supplemental method that better assesses the ingredient components of TCM preparations.We established an effective approach to screen the biological and toxical composition of TCM based on high-throughput sequencing (HTS), as well as fast detection and validation of the toxical species by real-time PCR, based on ITS2 DNA barcoding. Ruyi jinhuang powder (RHP), a classical herbal prescription containing the toxical herb Arisaematis rhizoma, was chosen to test the method. This method could determine whether the Arisaematis Rhizoma had been replaced by Pinellia pedatisecta in the RHP. The results were validated by real-time PCR. 90% compositions of RHP were identified by ITS2 DNA barcoding, suggesting that more DNA barcoding markers are needed for TCM identification. The strategy of high-throughput sequencing has the potential for comprehensive ingredient profiling for TCM preparations. Real-time PCR provides a expeditious metehod for monitoring the safety and legality of TCM preparations.

Transcriptional insights into the pyramided resistance to rice bacterial blight

The pyramiding of resistance (R) genes provides broad-spectrum and durable resistance to plant diseases. However, the genetic basis for bacterial blight (BB) resistance remains unclear. The BB R gene pyramided line IRBB54, which expresses xa5 and Xa21, possessed a higher level of resistance than both single R gene lines. Large-scale genotyping of genetic markers in this study revealed similar genetic backgrounds among the near-isogenic lines (NILs), suggesting that resistance in the resistant NILs was mainly conferred by the individual R genes or the interaction between them. Transcriptome analysis demonstrated that more than 50% of the differentially expressed genes (DEGs), and more than 70% of the differentially expressed functions, were shared between IRBB54 and IRBB5 or IRBB21. Most of the DEGs in the resistant NILs were downregulated and are predicted to function in cellular and biological process. The DEGs common among the resistant NILs mainly showed non-additive expression patterns and enrichment in stress-related pathways. The differential expression of agronomic trait-controlled genes in the resistant NILs, especially in IRBB54, indicated the existence of potential side-effects resulting from gene pyramiding. Our findings contribute to the understanding of R gene pyramiding, as well as its effects on targeted and non-targeted trait(s).