Deciphering Cis-Regulatory Element Mediated Combinatorial Regulation in Rice under Blast Infected Condition

Physiological and metabolic analyses reveal the proline-mediated flowering delay mechanism in Prunus persica

Peaches are susceptible to various environmental stresses. Particularly in late spring, freezing temperatures can damage peaches and consequently, affect their productivity. Therefore, flowering delay is a prominent strategy for avoiding spring frost damage. Our previous study confirmed that treatment with 5% sodium alginate and 100 mM CaCl2 (5AG) to avoid frost damage during the blooming stage delays flowering. To reveal the flowering delay mechanism of peaches, this study systematically analyzed the modification of amino acid profiles in control and 5AG-treated peach plants at different day intervals. Our findings indicate that arginine (Arg), glutamate (Glu), and proline (Pro) levels differed between the control and 5AG-treated peach shoots throughout the phenological development of flower buds. Furthermore, two amino acids (Arg and Glu) are involved in the Pro pathway. Thus, using a computational metabolomics method, Pro biosynthesis and its characteristics, gene ontology, gene synteny, cis-regulatory elements, and gene organizations were examined to decipher the involvement of Pro metabolism in peach flowering delay. In addition, qRT-PCR analysis revealed the transcriptional regulation of Pro-related and flowering-responsive genes and their role in flowering delay. Overall, this pilot study provides new insights into the role of Pro in the flowering delay mechanisms in Prunus persica through 5AG treatment.

Comprehensive Analysis and Characterization of the GATA Gene Family, with Emphasis on the GATA6 Transcription Factor in Poplar

GATA transcription factors are ubiquitously present in eukaryotic organisms and play a crucial role in multiple biological processes, such as plant growth, stress response, and hormone signaling. However, the study of GATA factors in poplar is currently limited to a small number of proteins, despite their evident functional importance. In this investigation, we utilized the most recent genome annotation and stringent criteria to identify 38 GATA transcription factor genes in poplar. Subsequently, we conducted a comprehensive analysis of this gene family, encompassing phylogenetic classification, protein characterization, analysis of promoter cis-acting elements, and determination of chromosomal location. Our examination of gene duplication events indicated that both tandem and segmental duplications have contributed to the expansion of the GATA gene family in poplar, with segmental duplication potentially being a major driving force. By performing collinearity analysis of genes across six different species, we identified 74 pairs of co-linear genes, which provide valuable insights for predicting gene functions from a comparative genomics perspective. Furthermore, through the analysis of gene expression patterns, we identified five GATA genes that exhibited differential expression in leaf-stem-root tissues and eight genes that were responsive to salt stress. Of particular interest was GATA6, which displayed strong induction by salt stress and overlapped between the two gene sets. We discovered that GATA6 encodes a nuclear-localized protein with transcription activation activity, which is continuously induced by salt stress in leaf and root tissues. Moreover, we constructed a co-expression network centered around GATA6, suggesting the potential involvement of these genes in the growth, development, and response to abiotic stress processes in poplar through cell transport systems and protein modification mechanisms, such as vesicle-mediated transport, intracellular transport, ubiquitination, and deubiquitination. This research provides a foundation for further exploration of the functions and mechanisms of GATA transcription factors in poplar.

Genome-Wide Characterization, Evolution, and Expression Profile Analysis of GATA Transcription Factors in Brachypodium distachyon

The GATA proteins, functioning as transcription factors (TFs), are involved in multiple plant physiological and biochemical processes. In this study, 28 GATA TFs of Brachypodium distachyon (BdGATA) were systematically characterized via whole-genome analysis. BdGATA genes unevenly distribute on five chromosomes of B. distachyon and undergo purifying selection during the evolution process. The putative cis-acting regulatory elements and gene interaction network of BdGATA were found to be associated with hormones and defense responses. Noticeably, the expression profiles measured by quantitative real-time PCR indicated that BdGATA genes were sensitive to methyl jasmonate (MeJA) and salicylic acid (SA) treatment, and 10 of them responded to invasion of the fungal pathogen Magnaporthe oryzae, which causes rice blast disease. Genome-wide characterization, evolution, and expression profile analysis of BdGATA genes can open new avenues for uncovering the functions of the GATA genes family in plants and further improve the knowledge of cellular signaling in plant defense.

Identification and Characterization of a Large Effect QTL from Oryza glumaepatula Revealed Pi68(t) as Putative Candidate Gene for Rice Blast Resistance

BACKGROUND

Field resistance is often effective and durable as compared to vertical resistance. The introgression line (INGR15002) derived from O. glumaepatula has proven broad spectrum field resistance for both leaf and neck blast.

RESULTS

Quantitative Trait Loci (QTL) analysis of INGR15002, led to the identification of two major QTL - qBL3 contributing about 34% and 32% phenotypic variance towards leaf and neck blast resistance, respectively and qBL7 contributing about 25% of phenotypic variance for leaf blast. Further, qBL3 was fine mapped, narrowed down to 300 kb region and a linked SNP maker was identified. By combining mapping with microarray analysis, a candidate gene, Os03g0281466 (malectin-serine threonine kinase), was identified in the fine mapped region and named as Pi68(t). The nucleotide variations in the coding as well as upstream region of the gene was identified through cloning and sequence analysis of Pi68(t) alleles. These significant variations led to the non-synonymous changes in the protein as well as variations (presence/absence) in four important motifs (W-box element; MYC element; TCP element; BIHD1OS) at promoter region those are associated with resistance and susceptible reactions. The effect of qBL3 was validated by its introgression into BPT5204 (susceptible variety) through marker-assisted selection and progeny exhibiting resistance to both leaf and neck blast was identified. Further, the utility of linked markers of Pi68(t) in the blast breeding programs was demonstrated in elite germplasm lines.

CONCLUSIONS

This is the first report on the identification and characterization of major effect QTL from O. glumaepatula, which led to the identification of a putative candidate gene, Pi68(t), which confers field resistance to leaf as well as neck blast in rice.

Genome-Wide Computational Identification of Biologically Significant Cis-Regulatory Elements and Associated Transcription Factors from Rice

The interactions between transcription factors (TFs) and cis-acting regulatory elements (CREs) provide crucial information on the regulation of gene expression. The determination of TF-binding sites and CREs experimentally is costly and time intensive. An in silico identification and annotation of TFs, and the prediction of CREs from rice are made possible by the availability of whole genome sequence and transcriptome data. In this study, we tested the applicability of two algorithms developed for other model systems for the identification of biologically significant CREs of co-expressed genes from rice. CREs were identified from the DNA sequences located upstream from the transcription start sites, untranslated regions (UTRs), and introns, and downstream from the translational stop codons of co-expressed genes. The biologically significance of each CRE was determined by correlating their absence and presence in each gene with that gene's expression profile using a meta-database constructed from 50 rice microarray data sets. The reliability of these methods in the predictions of CREs and their corresponding TFs was supported by previous wet lab experimental data and a literature review. New CREs corresponding to abiotic stresses, biotic stresses, specific tissues, and developmental stages were identified from rice, revealing new pieces of information for future experimental testing. The effectiveness of some-but not all-CREs was found to be affected by copy number, position, and orientation. The corresponding TFs that were most likely correlated with each CRE were also identified. These findings not only contribute to the prioritization of candidates for further analysis, the information also contributes to the understanding of the gene regulatory network.

Overexpression of Magnaporthe Oryzae Systemic Defense Trigger 1 (MoSDT1) Confers Improved Rice Blast Resistance in Rice

The effector proteins secreted by a pathogen not only promote virulence and infection of the pathogen, but also trigger plant defense response. Therefore, these proteins could be used as important genetic resources for transgenic improvement of plant disease resistance. Magnaporthe oryzae systemic defense trigger 1 (MoSDT1) is an effector protein. In this study, we compared the agronomic traits and blast disease resistance between wild type (WT) and MoSDT1 overexpressing lines in rice. Under control conditions, MoSDT1 transgenic lines increased the number of tillers without affecting kernel morphology. In addition, MoSDT1 transgenic lines conferred improved blast resistance, with significant effects on the activation of callose deposition, reactive oxygen species (ROS) accumulation and cell death. On the one hand, overexpression of MoSDT1 could delay biotrophy-necrotrophy switch through regulating the expression of biotrophy-associated secreted protein 4 (BAS4) and Magnaporthe oryzaecell death inducing protein 1 (MoCDIP1), and activate plant defense response by regulating the expression of Bsr-d1, MYBS1, WRKY45, peroxidase (POD), heat shock protein 90 (HSP90), allenoxide synthase 2 (AOS2), phenylalanine ammonia lyase (PAL), pathogenesis-related protein 1a (PR1a) in rice. On the other hand, overexpression of MoSDT1 could increase the accumulation of some defense-related primary metabolites such as two aromatic amino acids (L-tyrosine and L-tryptohan), 1-aminocyclopropane carboxylic acid, which could be converted to ethylene, vanillic acid and L-saccharopine. Taken together, overexpression of MoSDT1 confers improved rice blast resistance in rice, through modulation of callose deposition, ROS accumulation, the expression of defense-related genes, and the accumulation of some primary metabolites.

Shared cis-regulatory architecture identified across defense response genes is associated with broad-spectrum quantitative resistance in rice

Plant disease resistance that is durable and effective against diverse pathogens (broad-spectrum) is essential to stabilize crop production. Such resistance is frequently controlled by Quantitative Trait Loci (QTL), and often involves differential regulation of Defense Response (DR) genes. In this study, we sought to understand how expression of DR genes is orchestrated, with the long-term goal of enabling genome-wide breeding for more effective and durable resistance. We identified short sequence motifs in rice promoters that are shared across Broad-Spectrum DR (BS-DR) genes co-expressed after challenge with three major rice pathogens (Magnaporthe oryzae, Rhizoctonia solani, and Xanthomonas oryzae pv. oryzae) and several chemical elicitors. Specific groupings of these BS-DR-associated motifs, called cis-Regulatory Modules (CRMs), are enriched in DR gene promoters, and the CRMs include cis-elements known to be involved in disease resistance. Polymorphisms in CRMs occur in promoters of genes in resistant relative to susceptible BS-DR haplotypes providing evidence that these CRMs have a predictive role in the contribution of other BS-DR genes to resistance. Therefore, we predict that a CRM signature within BS-DR gene promoters can be used as a marker for future breeding practices to enrich for the most responsive and effective BS-DR genes across the genome.

Differentially Expressed MicroRNAs Link Cellular Physiology to Phenotypic Changes in Rice Under Stress Conditions

Plant microRNAs (miRNAs) and their target genes have important functional roles in nutrition deficiency and stress response. However, the underlying mechanisms relating relative expression of miRNAs and target mRNAs to morphological adjustments are not well defined. By combining miRNA expression profiles, corresponding target genes and transcription factors that bind to computationally identified over-represented cis-regulatory elements (CREs) common in miRNAs and target gene promoters, we implement a strategy that identifies a set of differentially expressed regulatory interactions which, in turn, relate underlying cellular mechanisms to some of the phenotypic changes observed. Integration of experimentally reported individual interactions with identified regulatory interactions explains how (i) during mineral deficiency osa-miR167 inhibits shoot growth but activates adventitious root growth by influencing free auxin content; (ii) during sulfur deficiency osa-miR394 is involved in adventitious root growth inhibition, sulfur and iron homeostasis, and auxin-mediated regulation of sulfur homeostasis; (iii) osa-miR399 contributes to cross-talk between cytokinin and phosphorus deficiency signaling; and (iv) a feed-forward loop involving the osa-miR166, trihelix and HD-ZIP III transcription factors may regulate leaf senescence during drought. This strategy not only identifies various regulatory interactions connecting phenotypic changes with cellular or molecular events triggered by stress, but also provides a framework to deepen our understanding of stress cellular physiology.

Activation of rice WRKY transcription factors: an army of stress fighting soldiers?

Rice WRKYs comprise a large family of transcription factors and present remarkable structure features and a unique DNA binding site. Their importance in plants goes beyond the response to stressful stimuli, since they participate in hormonal pathways and developmental processes. Indeed, the majority of WRKYs present an independent activation since they are able to perform self-transcriptional regulation. However, some WRKY activation depends on epigenetic and transcript regulation by micro RNAs. Their protein function depends, almost always, on the posttranslational changes. Taking to account its properties of auto-activation, all these regulators process are extremely important for complete WRKY regulation. In this sense, here we provide an overview of transcriptional activation and posttranscriptional and posttranslational regulation of rice WRKY genes under stresses.

Auxin Response Factors (ARFs) are potential mediators of auxin action in tomato response to biotic and abiotic stress (Solanum lycopersicum)

Survival biomass production and crop yield are heavily constrained by a wide range of environmental stresses. Several phytohormones among which abscisic acid (ABA), ethylene and salicylic acid (SA) are known to mediate plant responses to these stresses. By contrast, the role of the plant hormone auxin in stress responses remains so far poorly studied. Auxin controls many aspects of plant growth and development, and Auxin Response Factors play a key role in the transcriptional activation or repression of auxin-responsive genes through direct binding to their promoters. As a mean to gain more insight on auxin involvement in a set of biotic and abiotic stress responses in tomato, the present study uncovers the expression pattern of SlARF genes in tomato plants subjected to biotic and abiotic stresses. In silico mining of the RNAseq data available through the public TomExpress web platform, identified several SlARFs as responsive to various pathogen infections induced by bacteria and viruses. Accordingly, sequence analysis revealed that 5' regulatory regions of these SlARFs are enriched in biotic and abiotic stress-responsive cis-elements. Moreover, quantitative qPCR expression analysis revealed that many SlARFs were differentially expressed in tomato leaves and roots under salt, drought and flooding stress conditions. Further pointing to the putative role of SlARFs in stress responses, quantitative qPCR expression studies identified some miRNA precursors as potentially involved in the regulation of their SlARF target genes in roots exposed to salt and drought stresses. These data suggest an active regulation of SlARFs at the post-transcriptional level under stress conditions. Based on the substantial change in the transcript accumulation of several SlARF genes, the data presented in this work strongly support the involvement of auxin in stress responses thus enabling to identify a set of candidate SlARFs as potential mediators of biotic and abiotic stress responses.

Regulatory Cross-Talks and Cascades in Rice Hormone Biosynthesis Pathways Contribute to Stress Signaling

Crosstalk among different hormone signaling pathways play an important role in modulating plant response to both biotic and abiotic stress. Hormone activity is controlled by its bio-availability, which is again influenced by its biosynthesis. Thus, independent hormone biosynthesis pathways must be regulated and co-ordinated to mount an integrated response. One of the possibilities is to use cis-regulatory elements to orchestrate expression of hormone biosynthesis genes. Analysis of CREs, associated with differentially expressed hormone biosynthesis related genes in rice leaf under Magnaporthe oryzae attack and drought stress enabled us to obtain insights about cross-talk among hormone biosynthesis pathways at the transcriptional level. We identified some master transcription regulators that co-ordinate different hormone biosynthesis pathways under stress. We found that Abscisic acid and Brassinosteroid regulate Cytokinin conjugation; conversely Brassinosteroid biosynthesis is affected by both Abscisic acid and Cytokinin. Jasmonic acid and Ethylene biosynthesis may be modulated by Abscisic acid through DREB transcription factors. Jasmonic acid or Salicylic acid biosynthesis pathways are co-regulated but they are unlikely to influence each others production directly. Thus, multiple hormones may modulate hormone biosynthesis pathways through a complex regulatory network, where biosynthesis of one hormone is affected by several other contributing hormones.