Biology subjects

Hajirezaei, M.-R.

Publications and source records attributed to Hajirezaei, M.-R..

6 recordsLinked to original sources

bioRxiv2026

Programmed chromosome elimination correlates with the overexpression of cohesin and additional B chromosome-encoded genes in Aegilops speltoides

Programmed chromosome elimination is a highly controlled developmental process in which specific chromosomes are selectively lost from defined cell types during development. Despite its broad occurrence across plants and animals, the molecular mechanisms driving the tissue-specific elimination of chromosomes remain largely unresolved. Here, we exploit the root-specific elimination of supernumerary B chromosomes in Aegilops speltoides as a tractable model to identify the genetic basis of programmed chromosome loss. A high-quality, chromosome-scale genome assembly was generated, assigning 398 Mb of sequence to the Ae. speltoides B chromosome. Transcriptome profiling across seven tissue types representing chromosome elimination-active, elimination-negative, and B chromosome nondisjunction conditions identified 3,262 genes consistently upregulated in elimination-associated tissues, including 1,035 B genes. Stepwise subtraction of genes expressed in post-elimination and B chromosome-retaining reference tissues, followed by intersection with genes expressed during B nondisjunction in anthers, identified a candidate gene set enriched for chromosome segregation functions. From this set, we prioritized SYN2-B, a B chromosome-encoded cohesin -kleisin subunit whose Arabidopsis thaliana ortholog AtSYN2 induces chromosome bridges and micronucleus formation when misregulated. CENH3-B, an -type centromeric histone variant identified through GO enrichment analysis of B genes expressed in elimination-associated tissues, was shown to be incorporated in centromeres of both A and B chromosomes by transient gene expression assays using protoplasts and 3D structured illumination microscopy. These findings support a model in which B chromosome-encoded perturbations of cohesin activity and centromere composition contribute to selective B chromosome nondisjunction and their elimination in root tissues. Moreover, the SYN2-B promoter is enriched for ethylene response factor-binding sites compared to its A-encoded paralog, suggesting that ethylene is implicated in the root identity pathway driving root-specific B chromosome elimination.

genetics↗

bioRxiv2025

Light and chloroplast redox state modulate the progression of tobacco leaf infection by Pseudomonas syringae pv tabaci

Light significantly influences plant stress responses, with chloroplasts playing a pivotal role as both energy providers and light sensors. They communicate with the nucleus through retrograde signals, including secondary metabolites and reactive oxygen species (ROS). To investigate the contribution of chloroplast redox biochemistry to biotic responses, we studied the interactions of tobacco leaves expressing the alternative electron shuttle flavodoxin with virulent and nonhost Pseudomonas syringae pathovars under light and dark conditions. Flavodoxin is reported to limit light-dependent ROS propagation and over-reduction of the photosynthetic electron transport system under stress. Light intensified the hypersensitive response against the nonhost pathovar tomato (Pto), but slowed disease progression caused by the virulent pathovar tabaci (Pta). Flavodoxin mitigated light responses during both interactions, including decreased ROS levels, reduced stromule occurrence, and lower phytoalexin production, with different signatures depending on the pathovar. Similar leaf metabolic profiles were observed in the dark for both strains, with a general up-regulation of sugars, metabolic intermediates, and amino acids. In the light, instead, Pta increased sugars and intermediates, while Pto decreased them. Our results suggest that HR-like responses are elicited in the light even during virulent interactions, and that light effects are related to signals originating at the photosynthetic machinery. Highlights- Light inhibits disease progression during a tobacco-Pseudomonas virulent interaction. - Light exacerbates the hypersensitive response (HR) during a nonhost interaction. - HR-like responses are elicited in the light even during virulent interactions. - Plastid-targeted flavodoxin decreases plant damage only in photoperiod. - The chloroplast redox state modulates plant biotic response.

plant biology↗

bioRxiv2024

Elucidation and functional characterization of natural sweetener biosynthesis in hortensia species

Among the various coumarins found in Hydrangea species, the bioactive dihydroisocoumarin known as phyllodulcin (PD) stands out as a non-caloric, high-intensity sweetener, which is up to 800 times sweeter than sucrose. Additionally, PD possesses notable medicinal properties, including antifungal, anti-ulcer, and anti-inflammatory effects. PD also plays several plant-specific roles, such as defending against phytopathogens, responding to abiotic and biotic stresses and regulating hormones. However, the biological function and biosynthetic pathway of PD in Hydrangea remain unexplored. This study employs targeted metabolomic and transcriptomic approaches to uncover the regulatory mechanisms and identify potential candidate genes involved in the biosynthesis of PD. 14 out of 182 different Hydrangea accessions, exhibiting varying levels of PD, were selected for detailed analysis. Accessions of H. macrophylla with high PD levels displayed distinct metabolite profiles compared to those with low PD concentrations. Specifically, pathways involving caffeic acid, ferulic acid, and their derivatives, such as scopolin, scopoletin, esculetin, and fraxetin, were predominant in accessions with low PD concentrations. Conversely, the metabolism of phenylalanine, umbelliferone, p-coumaric acid, naringenin, resveratrol, and Thn C was more active in accessions containing PD. Correlation analysis between PD and these metabolites offered valuable insights into their interrelationships. Transcriptome analysis revealed specific genes involved in phenylpropanoid biosynthesis, flavonoid biosynthesis, and stilbene biosynthesis pathways that are crucial for PD biosynthesis. Moreover, the identification of cyclase and ketoreductase genes, which were up regulated in accessions with high PD, provided further understanding of the biosynthetic pathway leading to PD. Finally, based on metabolite levels and gene expression data, a hypothetical pathway from resveratrol to Thn C was proposed, suggesting its potential involvement in PD biosynthesis. HighlightThe metabolic and transcriptomic analysis led to the identification of specific metabolites and genes that are involved in the biosynthesis of dihydrisocoumarin.

plant biology↗

bioRxiv2022

Elucidating the systemic response of wheat plants under waterlogging based on transcriptomic and metabolic approaches

Extreme weather conditions lead to significant imbalances in crop productivity, which in turn affect food security. Flooding events cause serious problems to many crop species such as wheat. Although metabolic readjustments under flooding are important for plant regeneration, underlying processes remain poorly understood. Here, we investigated the systemic response of wheat to waterlogging using metabolomics and transcriptomics. A 12-day exposure to excess water triggered nutritional imbalances and disruption of metabolite synthesis and translocation, reflected by reduction of plant biomass and growth performance. Metabolic and transcriptomic profiling in roots, xylem, and leaves indicated anaerobic fermentation processes as a local response occurring in roots. Differentially expressed genes and ontological categories revealed that carbohydrate metabolism plays an important role as a systemic response. Analysis of the translocation rate of specific compounds in the xylem showed how waterlogging alters the composition of xylem exudates and thus the root to shoot communication. Interestingly, among all metabolites determined in our study, alanine was the most abundant transported in the xylem. Our results suggest an important role of this amino acid not only as amino-nitrogen source but also as the major root-to-shoot translocated and systemically acting metabolite crucial for balancing C/N between roots and shoots during waterlogging. The relevance of this study relies on the basis to characterize the important role of alanine as HighlightMetabolic and transcriptomic changes in wheat highlight alanine as the major root-to-shoot translocated and systemically acting metabolite crucial for balancing C/N between roots and shoots.

physiology↗

bioRxiv2022

Chloroplast redox status modulates the cell expansion phase of leaf development associated to changes in proteasome activity and endoreduplication index

Foliar development involves successive phases of cell proliferation and expansion that determine the final leaf size, and is characterized by an early burst of reactive oxygen species (ROS) generated in the photosynthetic electron transport chain (PETC). Introduction of the alternative PETC acceptor flavodoxin in tobacco chloroplasts led to a reduction in leaf size associated to lower cell expansion, without affecting cell numbers per leaf. Proteomic analysis showed that components of the light-harvesting systems accumulated before electron-transport proteins, suggesting a mechanism for the early oxidative event. Flavodoxin expression did not affect biogenesis of the PETC but prevented ROS build-up through its function as electron sink. Mature leaves from flavodoxin-expressing plants were shown to contain higher levels of transcripts encoding components of the proteasome, a key negative modulator of organ size. Proteome profiling revealed that this differential accumulation initiated during expansion and led to increased proteasomal activity, whereas a proteasome inhibitor reverted the flavodoxin-dependent size phenotype. Cells expressing plastid-targeted flavodoxin displayed lower endoreduplication, also associated to decreased organ size. These results provide novel insights into the regulation of leaf growth by chloroplast-generated redox signals, and highlight the potential of alternative electron shuttles to investigate novel link(s) between photosynthesis and plant development. HighlightModification of chloroplast redox status by expression of the cyanobacterial alternative electron sink flavodoxin decreased leaf cell expansion, which was associated with higher proteasome activity and lower endoreduplication.

plant biology↗

bioRxiv2020

Providing an additional electron sink by the introduction of cyanobacterial flavodiirons enhances the growth of Arabidopsis thaliana in varying light

The ability of plants to maintain photosynthesis in a dynamically changing environment is of central importance for their growth. As their photosynthetic machinery typically cannot adapt rapidly to fluctuations in the intensity of radiation, the level of photosynthetic efficiency is not always optimal. Cyanobacteria, algae, non-vascular plants (mosses and liverworts) and gymnosperms all produce flavodiirons (Flvs), a class of proteins not represented in the angiosperms; these proteins act to mitigate the photoinhibition of photosystem I. Here, genes specifying two cyanobacterial Flvs have been expressed in the chloroplasts of Arabidopsis thaliana in an attempt to improve the robustness of Photosystem I (PSI). The expression of Flv1 and Flv3 together shown to enhance the efficiency of the utilization of light and to boost the plants capacity to accumulate biomass. Based on an assessment of the chlorophyll fluorescence in the transgenic plants, the implication was that photosynthetic activity (including electron transport flow and non-photochemical quenching during a dark-to-light transition) was initiated earlier in the transgenic than in wild type plants. The improved photosynthetic performance of the transgenics was accompanied by an increased production of ATP, an acceleration of carbohydrate metabolism and a more pronounced partitioning of sucrose into starch. The indications are that Flvs are able to establish an efficient electron sink downstream of PSI, thereby ensuring that the photosynthetic electron transport chain remains in a more oxidized state. The expression of Flvs in a plant acts to both protect photosynthesis and to control the ATP/NADPH ratio; together, their presence is beneficial for the plants growth potential.

biochemistry↗