Biology subjects

Dassanayake, M.

Publications and source records attributed to Dassanayake, M..

25 records · Page 2Linked to original sources

bioRxiv2020

Cross species multi-omics reveals cell wall sequestration and elevated global transcription as mechanisms of boron tolerance in plants

Boron toxicity is a worldwide problem for crop production, yet we have only a limited understanding of the genetic responses and adaptive mechanisms to this environmental stress in plants. Here we identified responses to excess boron in boron stress-sensitive Arabidopsis thaliana and its boron stress-tolerant extremophyte relative Schrenkiella parvula using comparative genomics, transcriptomics, metabolomics, and ionomics. S. parvula maintains a lower level of total boron and free boric acid in its roots and shoots and sustains growth for longer durations than A. thaliana when grown with excess boron. S. parvula likely excludes boron more efficiently than A. thaliana, which we propose is partly driven by BOR5, a boron transporter that we functionally characterized in the current study. Both species allocate significant transcriptomic and metabolomic resources to enable their cell walls to serve as a partial sink for excess boron, particularly discernable in A. thaliana shoots. We provide evidence that the S. parvula transcriptome is pre-adapted to boron toxicity, exhibiting substantial overlap with the boron-stressed transcriptome of A. thaliana. Our transcriptomic and metabolomics data also suggest that RNA metabolism is a primary target of boron toxicity. Cytoplasmic boric acid likely forms complexes with ribose and ribose-containing compounds critical to RNA and other primary metabolic functions. A model depicting some of the cellular responses that enable a plant to grow in the presence of normally toxic levels of boron is presented.

plant biology↗

bioRxiv2020

A tale of two transcriptomic responses in agricultural pests via host defenses and viral replication

BackgroundAutographa californica Multiple Nucleopolyhedrovirus (AcMNPV) is a baculovirus with a high potential for its use as a biopesticide against arthropod pests. The budded form of the virus causes a systemic infection when it escapes the midgut to enter the hemolymph of susceptible hosts. Yet, the specific molecular processes underlying the biocidal activity of AcMNPV on its insect hosts are largely unknown. ResultsIn this study, we describe the transcriptional responses in two major pests, Spodoptera frugiperda and Trichoplusia ni, to determine the host-pathogen responses during AcMNPV infection, concurrently with the viral response to the host. We assembled species-specific de novo reference transcriptomes of the hemolymph to identify key transcripts that respond during pathogenesis in these arthropod models where genomic resources are sparse. We found that the suppression of transcriptional processes related to chitin, a metabolite critical for basement membrane stability and tracheal development are central in establishing a systemic infection. Synergistic transcriptional support was observed to suggest suppression of immune responses and induction of oxidative stress indicating disease progression in the host. The entire AcMNPV core genome was expressed in the host hemolymph and viral genes predominantly associated with the budded virus replication, structure, and movement were more abundant than those associated with the occlusion-derived virus. Genes known to directly arrest host cell cycle and development were among the most abundant AcMNPV transcripts in infected hosts. Interestingly, several of the host genes (e.g. Chitin synthase) that were targeted by the pathogen as revealed by our study are also targets of several chemical insecticides currently used commercially to control arthropod pests. ConclusionsOur results reveal an extensive overlap between biological processes represented by genes differently expressed in both hosts, as well as convergence on highly abundant viral genes expressed in the two hosts, providing an overview of the host-pathogen transcriptomic landscape during systemic infection. Given the diversity of AcMNPV strains that infect a wide range of insect hosts, our study provides a framework where pathogen strains could be selected to target specific host genes that facilitates modulation of the infection strength and specificity of the susceptible hosts.

genomics↗

bioRxiv2019

A RETINOBLASTOMA-RELATED transcription factor network governs egg cell differentiation and stress response in Arabidopsis

The multicellular embryo, and ultimately the entire organism, is a derivative of the fertilized egg cell. Unlike in animals, transcription factor networks orchestrating faithful egg development are still largely unknown in plants. We have identified that egg cell differentiation in Arabidopsis require interplay between evolutionarily conserved onco-protein homologs RETINOBLASTOMA-RELATED (RBR) and redundant MYB proteins MYB64/MYB119. RBR physically interacts with the MYBs; and with plant-specific transcription factors belonging to the RWP-RK-domain (RKD) family and LEAFY COTYLEDON1 (LEC1), which participate in development of egg cells and inherent stress response. RBR binds to most of these egg cell-expressed loci at the DNA level, partially overlapping with sites of histone methylation H3K27me3. Since deregulation of RKDs phenocopies mutants of RBR and the MYBs in terms of cell proliferation in the egg cell spatial domain, all the corresponding proteins are likely required to restrict parthenogenetic cell divisions of the egg cells. Cross-talk among these transcription factors, and direct regulation by RBR, govern egg cell development and expression of egg-to-zygotic polarity factors of the WUSCHEL RELATED HOMEOBOX family. Together, a network of RBR-centric transcription factors underlies egg cell development and stress response, possibly, in combination with several other predicted nodes.\n\nAuthor summaryThe RETINOBLASTOMA protein is one of the core components of the Eukaryotic cell cycle, and corresponding evolutionary homologs have been implicated not only to repress cell division but also to control differentiation and development. How RETINOBLASTOMA RELATED (RBR) associate with other higher order regulators to control faithful egg cell development in sexual plants is pivotal for manipulation of successful reproduction in general, and engineering of parthenogenesis when asexual or apomictic seed progeny are desirable over sexual plants. Using a suite of molecular methods, we show that a RBR-associated transcription factor network operates to specify egg cells in Arabidopsis. Complex cross-regulation within these transcription factors seems to be necessary for successful maternal egg cell to zygotic transition and reproductive stress response. Detailed genetic analysis implicate that RBR and its interactive partners belonging to MYB and RWP-RK transcription factor families are possibly required to prevent parthenogenesis of the sexual egg cells. Novel RBR networks and stress nodes explained in this study might help to improve our understanding of sexual and asexual reproduction.

genetics↗

bioRxiv2019

Molecular responses to freshwater limitation in the mangrove tree Avicennia germinans (Acanthaceae)

Environmental variation along the geographical space can shape populations by natural selection. In the context of global warming, accompanied by substantial changes in precipitation regimes, it is crucial to understand the role of environmental heterogeneity in tropical trees adaptation, given their disproportional contribution to water and carbon biogeochemical cycles. Here we investigated how heterogeneity in freshwater availability along tropical wetlands has influenced molecular variations of the Black-Mangrove (Avicennia germinans). Fifty-seven trees were sampled in seven sites differing markedly on precipitation regime and riverine freshwater inputs. Using 2,297 genome-wide single nucleotide polymorphic markers, we found signatures of natural selection by the genotype association with the precipitation of the warmest quarter and the annual precipitation. We also found candidate loci for selection, based on statistical deviations from neutral expectations of interpopulation differentiation. Most candidate loci present within coding sequences were functionally associated with central aspects of drought-tolerance or plant response to drought. Complementarily, our results suggest the occurrence of rapid evolution of a population, likely in response to sudden and persistent limitation in plant access to soil water, following a road construction in 1974. Observations supporting rapid evolution included reduction in tree size and changes in allele frequencies and in transcripts expression levels associated with increased drought-tolerance, through accumulation of osmoprotectants and antioxidants, biosynthesis of plant cuticle, protection against stress-induced proteins degradation, stomatal closure, photorespiration and photosynthesis. We describe a major role of spatial heterogeneity in freshwater availability in the specialization of this typically tropical tree.

evolutionary biology↗

bioRxiv2019

Defining chromatin state transitions predicts a network that modulates cell wall remodeling in phosphate-starved rice shoots

Phosphorus (P) is an essential plant macronutrient vital to fundamental metabolic processes. Plant-available P is low in most soils, making it a frequent limiter of growth. Declining P reserves for fertilizer production exasperates this agricultural challenge. Plants modulate complex responses to fluctuating P levels via global transcriptional regulatory networks. Although chromatin structure plays a substantial role in controlling gene expression, the chromatin dynamics involved in regulating P homeostasis have not been determined. Here we define distinct chromatin states across the rice genome by integrating multiple aspects of chromatin structure, including the H2A.Z histone variant, H3K4me3 modification, and nucleosome positioning. In response to P starvation, 40% of all protein-coding genes exhibit a transition from one chromatin state to another at their transcription start site. Several of these transitions are enriched in subsets of genes differentially expressed by P deficiency. The most prominent subset supports the presence of a coordinated signaling network that targets cell wall structure and is regulated in part via a decrease of H3K4me3 at the transcription start site. The P-starvation induced chromatin dynamics and correlated genes identified here will aid in enhancing P-use efficiency in crop plants, benefitting global agriculture.\n\nOne sentence summaryCombining data for three components of chromatin structure from control and phosphate-starved rice shoots reveals specific chromatin state transitions that correlate with subsets of functionally distinct differentially-expressed genes.

plant biology↗

bioRxiv2018

Environment-driven genomic and trait divergence in a neotropical mangrove highlight differential sensitivities to climate change

Local adaptation is often a product of environmental variations in the geographical space and has implications for biodiversity conservation. We investigated the role of latitudinal heterogeneity in climate on the organization of genetic and phenotypic variation in the dominant coastal tree, Avicennia schaueriana. In a common garden experiment, samples from an equatorial region, marked by rainy/dry seasons, accumulated less biomass, showed lower stomatal conductance and transpiration, narrower xylem vessels, smaller leaves and higher reflectance of long wavelengths (red light) on the stem epidermis, than samples from a subtropical region, marked by warm/cold seasons. Transcriptome differences identified between trees sampled under field conditions at equatorial and subtropical sites, were enriched in functional categories as responses to temperature, solar radiation, water deficit, photosynthesis and cell wall biosynthesis. The diversity based on thousands of SNP loci revealed a north-south genetic structure. Remarkably, signatures of selection were identified in loci associated with photosynthesis, anthocyanin accumulation and the responses to osmotic and hypoxia stresses. Our results suggest the existence of divergence in key resource-use characteristics, likely driven by climate seasonality, based on water-deficit and solar radiation. These findings provide a basis for conservation plans and for predictions for coastal plant responses to climate change.

plant biology↗

bioRxiv2017

Network of orthologs and evolutionary context search unveil the landscape of gene transposition-duplication within the Brassicaceae family.

We developed the CLfinder-OrthNet pipeline that detects co-linearity in gene arrangement among multiple closely related genomes; find ortholog groups; and encodes the evolutionary history of each ortholog group into a representative network (OrthNet). Using a search based on network topology, out of a total of 17,432 OrthNets in six Brassicaceae genomes, we identified 1,394 that included gene transposition-duplication (tr-d) events in one or more genomes. Occurrences of tr-d shared by subsets of Brassicaceae genomes mirrored the divergence times between the genomes and their repeat contents. The majority of tr-d events resulted in truncated open reading frames (ORFs) in the duplicated loci. However, the duplicates with complete ORFs were significantly more frequent than expected from random events. They also had a higher chance of being expressed and derived from older tr-d events. We also found an enrichment, compared to random chance, of tr-d events with complete loss of intergenic sequence conservation between the original and duplicated loci. Finally, we identified tr-d events uniquely found in two extremophytes among the six Brassicaceae genomes, including tr-d of SALT TOLERANCE 32 and ZINC TRANSPORTER 3. The CLfinder-OrthNet pipeline provides a flexible and a modular toolkit to compare gene order, encode and visualize evolutionary paths among orthologs as networks, and identify all gene loci that share the same evolutionary history using network topology searches.\n\nFunding source: This work was supported by National Science Foundation (MCB 1616827) and the Next Generation BioGreen21 Program (PJ011379) of the Rural Development Administration, Republic of Korea.\n\nOnline-only Supplementary materials includes supplementary text (S1-S10), methods (M1-M4), figures (S1-S7), and tables (S1-S3), in two PDF files, one for text and methods and the other for figures and tables. Additionally, Supplementary Dataset S1 is available at the Figshare repository (https://doi.org/10.6084/m9.figshare.5825937) and Dataset S2 and S3 as separate Excel files.

genomics↗