Biology subjects

Merai, Z.

Publications and source records attributed to Merai, Z..

7 recordsLinked to original sources

bioRxiv2026

An experimentally tractable Arabidopsis-Swede Midge model to explore host reprogramming by gall-inducing insects

Insect-induced galls are striking examples of host developmental reprogramming, yet their causal mechanisms remain poorly understood because few insect gall systems combine experimental tractability with precise control of insect and host developmental state. Here, we establish Arabidopsis thaliana and the gall-inducing Swede Midge (Contarinia nasturtii) as an experimental system for insect gall research. We show that the Swede Midge, a major pest of Brassica crops, completes its full life cycle on Arabidopsis, and induces characteristic inflorescence galls. To define and quantify galling while accounting for changes in developmental stage in both partners, we developed three complementary approaches. On the insect side, a larval phenotyping pipeline monitors how many larvae are present and how far they have developed, and a larval droplet assay delivers defined numbers of stage-selected larvae directly to host inflorescences, fixing the insect input and establishing a precise time zero for the interaction. We found that early-stage larvae can induce galls, whereas late-stage larvae (L3) cannot, defining the developmental window for gall induction. On the host side, we established a phyllotactic dissection and staging framework that enables galled and non-galled floral tissues to be compared at defined developmental positions. We found that galling enlarged floral buds, floral primordia and the inflorescence meristem while delaying floral developmental progression, with accompanying changes in cell size, shape and tissue organisation. Together, these tools combine Arabidopsis genetics with controlled insect manipulation, opening the way to mechanistic dissection of how insects reprogram plant pathways.

plant biology↗

bioRxiv2025

Antagonism between blue and red light-signalling controls thallus flatness in Marchantia polymorpha

The growth orientation of the Marchantia polymorpha thallus - a system of dorsiventralized, indeterminate axes - is modulated by light. We show that red and blue light act antagonistically to control thallus growth tropisms, with red light signalling promoting epinasty and blue light signalling promoting hyponasty. We found that loss-of-function mutations in the blue light receptor MpPHOT led to epinasty, while loss-of-function mutations in the red light receptor MpPHY resulted in hyponasty. We hypothesize that these antagonistic activities of blue and red light signalling are balanced in white light, resulting in the development of flat thalli. Using time-resolved transcriptomics, we identified genes that were rapidly induced upon light exposure. Among these genes were all six members of the M. polymorpha BBX gene family. Mutants harbouring loss-of-function mutations in two of the six MpBBX transcription factors developed defective thallus tropisms. Mpbbx1 loss-of-function mutants formed hyponastic thalli, while Mpbbx5 loss-of-function mutants developed epinastic thalli. Double mutants Mpbbx1 Mpbbx5 grew flat, supporting the hypothesis that they function antagonistically. Together, these data indicate that phototropin-mediated blue light and phytochrome-mediated red light signalling antagonistically modulate thallus tropism, and that BBX transcription factors also act antagonistically to regulate thallus flatness.

plant biology↗

bioRxiv2025

Phytochrome A is required for light-inhibited germination of Aethionema arabicum seed

O_LIThe germination of most seeds is influenced by the duration, intensity, and quality of light. The seeds of the model plant Arabidopsis are positive photoblastic and require light to germinate. The germination of negative photoblastic seeds is inhibited by white light. The molecular mechanisms that regulate negative photoblastic germination are unknown due to the lack of a suitable model plant. C_LIO_LIWe identified an accession with negative photoblastic germination in Aethionema arabicum that grows in semi-arid natural habitats. In a forward genetic screen, we identified a mutant - koyash2 (koy2) - that is defective in negative photoblastic germination. There is a nonsense mutation in the gene encoding the phytochrome A photoreceptor in the koy2 mutant. C_LIO_LIHere we show that phytochrome A is required for negative photoblastic germination. The defective negative photoblastic phenotype of the koy2 mutant is the result of defective inhibition of germination by the phytochrome A mediated high-irradiance response. C_LIO_LIThis is the first example of phytochrome A-mediated response controlling negative photoblastic seed germination in white, red, far-red, and blue light. We speculate that genetically encoded variation in phytochrome A-mediated germination responses is responsible for local adaptation of Ae. arabicum throughout the Irano-Turanian region. C_LI One sentence summaryIdentification and characterization of a phytochrome A null mutant demonstrates an active role of phytochrome A in light-inhibited seed germination in Aethionema arabicum, a negative photoblastic Mediterranean plant.

plant biology↗

bioRxiv2024

Long days induce adaptive secondary dormancy in seed of the Mediterranean plant Aethionema arabicum

Secondary dormancy is an adaptive trait that increases reproductive success by aligning seed germination with permissive conditions for seedling establishment. Aethionema arabicum is an annual plant and member of the Brassicaceae that grows in environments characterized by hot and dry summers. Aethionema arabicum seeds may germinate in early spring when seedling establishment is permissible. We demonstrate that long-day light regimes induce secondary dormancy in seed of Aethionema arabicum (CYP accession) repressing germination in summer when seedling establishment is riskier. Characterization of mutants screened for defective secondary dormancy demonstrated that RGL2 mediates repression of genes involved in GA signalling. Exposure to high temperature alleviates secondary dormancy, restoring germination potential. These data are consistent with the hypothesis that long-day-induced secondary dormancy and its alleviation by high temperatures, may be part of an adaptive response limiting germination to conditions permissive for seedling establishment in spring and autumn.

plant biology↗

bioRxiv2023

The dimorphic diaspore model Aethionema arabicum (Brassicaceae): Distinct molecular and morphological control of responses to parental and germination temperatures

Plants in habitats with unpredictable conditions are often characterized by diversifying their bet-hedging strategies that ensure fitness over a wider range of variable environmental factors. A striking example is the diaspore (seed and fruit) heteromorphism that evolved to maximize species survival in Aethionema arabicum (Brassicaceae) in which external and endogenous triggers allow the production of two distinct diaspores on the same plant. Using this dimorphic diaspore model, we identified contrasting molecular, biophysical, and ecophysiological mechanisms in the germination responses to different temperatures of the mucilaginous seeds (M+ seed morphs), the dispersed indehiscent fruits (IND fruit morphs), and the bare non-mucilaginous M- seeds obtained by pericarp (fruit coat) removal from IND fruits. Large-scale comparative transcriptome and hormone analyses of M+ seeds, IND fruits, and M- seeds provided comprehensive datasets for their distinct thermal responses. Morph-specific differences in co-expressed gene modules in seeds, as well as seed and pericarp hormone contents identified a role of the IND pericarp in imposing coat dormancy by generating hypoxia affecting ABA sensitivity. This involved expression of morph-specific transcription factors, hypoxia response and cell wall-remodeling genes, as well as altered abscisic acid (ABA) metabolism, transport, and signaling. Parental temperature affected ABA contents and ABA-related gene expression and altered IND pericarp biomechanical properties. Elucidating the molecular framework underlying the diaspore heteromorphism can provide insight into developmental responses to globally changing temperatures. IN A NUTSHELL BackgroundHeteromorphic diaspores (fruits and seeds) are an adaptive bet-hedging strategy to ensure survival in spatiotemporally variable environments. The stone cress Aethionema arabicum, an annual plant native to semi-arid habitats in Anatolia (Turkey), one of the worlds hotspots of biodiversity. It is a close relative of Arabidopsis, rapeseed, cabbage and other Brassica crops, but in contrast to these Ae. arabicum disperses two distinct diaspores from the same plant. These dimorphic diaspores are the mucilaginous seeds (dispersed by pod shatter) and indehiscent fruits (dispersed by abscission). The wing-like pericarp (fruit coat) of the single-seeded indehiscent fruit allows wind dispersal over large distances. The amounts and ratios of the dimorphic diaspores are variable and depend on the environmental conditions. The dimorphic diaspores differ in morphology, dormancy and germination properties and thereby make Ae. arabicum an excellent model for the comparative investigation of the underpinning molecular mechanisms. QuestionWe asked how temperature during fruit and seed formation and during seed germination affect dormancy release and germination speed, and how the morphology, hormonal regulation, and the expression of genes differ between the dimorphic diaspores. FindingsLarge-scale comparative transcriptome and hormone analyses of the mucilaginous seeds and the indehiscent fruits, as well as the seeds artificially extracted from indehiscent fruits by pericarp (fruit coat) removal, provided comprehensive datasets for their distinct thermal responses. Material obtained from plants grown at different temperatures during reproduction was imbibed at different temperatures for germination. This altered the abscisic acid (ABA) metabolism and the pericarp biomechanical properties. Diaspore-specific differences in response to distinct imbibition temperatures identified distinct gene expression patterns in seeds, distinct seed and pericarp hormone contents, and a role of the pericarp in generating hypoxia inside the fruit and imposing coat dormancy. This revealed distinct combinations of specific transcription factors, hypoxia responses and cell wall-remodeling genes, as well as altered signaling pathway genes. Next stepsOur large-scale comparative transcriptome datasets are easily and publicly accessible via the Aethionema arabicum web portal (https://plantcode.cup.uni-freiburg.de/aetar_db/index.php). We plan to expand this by future work on seedlings derived from the dimorphic diaspores, by comparing different Ae. arabicum genotypes, and by studying responses to specific stresses. Understanding the molecular basis of this fascinating example of developmental diversity and plasticity and its regulation by temperature is expected to add insight how plants respond to changing environmental conditions.

plant biology↗

bioRxiv2022

Phytochromes mediate germination inhibition under red, far-red, and white light in Aethionema arabicum

The view on the role of light during seed germination stems mainly from studies with Arabidopsis, where light is required to initiate this process. In contrast, white light is a strong inhibitor of germination in other plants, exemplified by accessions of Aethionema arabicum, another Brassicaceae. Their seeds respond to light with gene expression changes of key regulators converse to Arabidopsis, resulting in antipodal hormone regulation and prevention of germination. The photoreceptors involved in this process in A. arabicum were unknown. Screening the first mutant collection of A. arabicum, we identified koy-1, a mutant that lost light inhibition of germination, due to a deletion in the promoter of HEME OXYGENASE 1, the gene for a key enzyme in the biosynthesis of the phytochrome chromophore. koy-1 seeds are unresponsive to red- and far-red light and hyposensitive under white light. Comparison of hormone and gene expression between wild type and koy- 1 revealed that very low light fluence stimulates germination, while high irradiance of red and far-red light is inhibitory, indicating a dual role of phytochromes in light-regulated seed germination. The mutation also affects the ratio between the two fruit morphs of A. arabicum, suggesting that light reception via phytochromes can fine-tune several parameters of propagation in adaptation to conditions in the habitat. One sentence summaryCharacterization of a phytochrome chromophore biosynthesis mutant demonstrates an active role of phytochromes in the light-inhibited seed germination in Aethionema arabicum.

plant biology↗

bioRxiv2018

A novel model plant to study the light control of seed germination

Timing of seed germination is crucial for seed plants and coordinated by internal and external cues, reflecting adaptations to different habitats. Physiological and molecular studies with lettuce and Arabidopsis thaliana have documented a strict requirement for light to initiate germination and identified many receptors, signalling cascades, and hormonal control elements. In contrast, seed germination of several other plants is inhibited by light, but the molecular basis of this converse response is unknown. We describe Aethionema arabicum (Brassicaceae) as a suitable model plant to investigate the mechanism of germination inhibition by light, as it comprises accessions with natural variation between light-sensitive and light-neutral responses. Inhibition is independent of light wavelength and increases with light intensity and duration. Gibberellins and abscisic acid are involved in the control of germination as in Arabidopsis, but transcriptome comparisons of light- and dark-exposed Aethionema arabicum seeds revealed that expression of genes for key regulators upon light exposure undergo converse changes, resulting in antipodal hormone regulation. This illustrates that similar modular components of a pathway in light-inhibited, light-neutral and light requiring germination among the Brassicaceae have been assembled by evolution to produce divergent pathways, likely as adaptive traits.\n\nHighlightIn contrast to light requirement for Arabidopsis seed germination, germination of several Aethionema arabicum accessions is inhibited by light, due to antipodal transcriptional regulation of hormone balance.

plant biology↗