Biology subjects

Drakakaki, G.

Publications and source records attributed to Drakakaki, G..

9 recordsLinked to original sources

bioRxiv2025

Key molecular and cellular events of table olive fruit abscission zone formation during natural maturation and after ethephon treatment

Abscission zones are specialized cell layers that enable organ detachment, yet their morphology and regulation vary among species. Olive (Olea europaea), a non-climacteric fruit, requires high concentrations of ethylene-releasing compounds to reduce fruit removal force (FRF) for mechanical harvest. To elucidate mechanisms of fruit abscission zone (FAZ) development in olive, we integrated physiological, transcriptomic, and cellular analyses during natural maturation and after ethephon treatment. Olive fruits emitted low ethylene at color transition, coinciding with declining FRF, and application of 1500 ppm ethephon reduced FRF after one week. Transcriptome analyses of FAZ tissues, using a mesocarp-subtraction strategy to isolate FAZ-specific responses, identified 733 FAZ-specific genes shared between natural maturation and ethephon treatments, including genes of {beta}-1,3-glucanases, pectate lyases, and the phenylpropanoid pathway. Microscopy revealed lignification and alkalization of FAZ, accompanied by reduced low-methylesterified homogalacturonan and non-fucosylated xyloglucan. Increased glucanase activity and reduction in plasmodesmata callose likely facilitate cellular communication during abscission. Further, this study provides the first evidence of FAZ alkalization and implicates transporter upregulation in pH regulation preceding abscission. Our findings advance understanding of abscission biology in non-climacteric fruits and delineate conserved features of FAZ development. Summary StatementIntegrated physiological, transcriptomic, and cellular analyses reveal that fruit abscission zone development in olive involves lignification, alkalization, and coordinated cell wall remodeling, identifying {beta}-1,3-glucanases, pH-regulating transporters, and pectate lyases that facilitate cell separation in a non-climacteric fruit.

plant biology↗

bioRxiv2025

Cell layer-specific modification of cell wall is associated with exo-mesocarp split in pistachio (Pistacia vera L.)

Pistachio (Pistacia vera) is a drought and salinity-tolerant perennial whose fruit features a fleshy exo-mesocarp, or "hull," that protects the kernel. Hull development and degradation are key to kernel quality, yet the anatomy and mechanisms driving hull breakdown during late-stage development remain largely unknown. Here, we show that the hull contains anatomically distinct layers of hypodermal parenchyma and filler parenchyma. Using a combination of transcriptome analyses and immunohistochemistry, we show that changes in pectin associated gene expression and modification of this polysaccharide are involved in hull cell size increase, loss of cell-cell adhesion, and softening. Anatomical analysis shows that filler parenchyma expands during late-stage hull development while hypodermal parenchyma remains constant in size. Field data suggest that irrigation and humidity affect pistachio hull split, implicating a role for water status in cell expansion. In summary, the complex interplay between molecular, cellular, and environmental changes suggests that cell layer-specific modifications of the cell wall are linked to exo-mesocarp splitting, forming a model for understanding the mechanism of fruit split during ripening in non-berry fruit crops. HighlightCell-layer specific modifications of the cell wall are associated with cell expansion and loss of cell-cell adhesion, leading to hull split during late-stage pistachio fruit development.

plant biology↗

bioRxiv2024

In a nutshell: pistachio genome and kernel development

Pistachio is a sustainable nut crop with exceptional climate resilience and nutritional value. To advance pistachios as a future food source and a model system for hard-shelled fruits, we generated a chromosome-scale reference genome of the most widely grown pistachio cultivar (Pistacia vera Kerman) and a spatiotemporal developmental study of the hull, shell, and kernel. Our study defined four distinct stages of pistachio growth and maturation by integrating tissue-level physiological and molecular data from thousands of nuts across twenty-four time points over three growing seasons. Transcriptional and metabolic changes in the kernel elucidate molecular pathways governing nutritional quality, such as the accumulation of unsaturated fatty acids, which are vital for shelf-life and dietary value. This work yields new knowledge and resources that will inform other woody crops and facilitate further improvement of pistachio as a globally significant, sustainable, and nutritious crop.

plant biology↗

bioRxiv2024

Natural variation in salt-induced changes in root:shoot ratio reveals SR3G as a negative regulator of root suberization and salt resilience in Arabidopsis

Soil salinity is one of the major threats to agricultural productivity worldwide. Salt stress exposure alters root and shoot growth rates, thereby affecting overall plant performance. While past studies have extensively documented the effect of salt stress on root elongation and shoot development separately, here we take an innovative approach by examining the coordination of root and shoot growth under salt stress conditions. Utilizing a newly developed tool for quantifying the root:shoot ratio in agar-grown Arabidopsis seedlings, we found that salt stress results in a loss of coordination between root and shoot growth rates. We identify a specific gene cluster encoding domain-of-unknown-function 247 (DUF247), and characterize one of these genes as Salt Root:shoot Ratio Regulator Gene (SR3G). Further analysis elucidates the role of SR3G as a negative regulator of salt stress tolerance, revealing its function in regulating shoot growth, root suberization, and sodium accumulation. We further characterize that SR3G expression is modulated by WRKY75 transcription factor, known as a positive regulator of salt stress tolerance. Finally, we show that the salt stress sensitivity of wrky75 mutant is completely diminished when it is combined with sr3g mutation. Together, our results demonstrate that utilizing root:shoot ratio as an architectural feature leads to the discovery of new stress resilience gene. The studys innovative approach and findings not only contribute to our understanding of plant stress tolerance mechanisms but also open new avenues for genetic and agronomic strategies to enhance crop environmental resilience.

plant biology↗

bioRxiv2023

Four-dimensional quantitative analysis of cell plate development using lattice light sheet microscopy identifies robust transition points between growth phases

Cell plate formation during cytokinesis entails multiple stages occurring concurrently and requiring orchestrated vesicle delivery, membrane remodeling, and timely polysaccharide deposition, such as callose. Such a dynamic process requires dissection in time and space; hence this has been a major hurdle in studying cytokinesis. Using lattice light sheet microscopy (LLSM) we studied cell plate development in four dimensions, monitored by the behavior of the cytokinesis specific GTPase RABA2a. We monitored the entire length of cell plate development, from its first emergence, with the aid of RABA2a, both in the presence and absence of cytokinetic callose. By developing a robust cytokinetic vesicle volume analysis, we identified distinct behavioral patterns allowing for the identification of three easily trackable, cell plate developmental phases. Notably, the phase transition between phase I and phase II is striking, indicating a switch from membrane accumulation to the recycling of excess membrane material. We interrogated the role of callose using pharmacological inhibition with LLSM and electron microscopy. Loss of callose inhibited phase transition, establishing quantitatively the critical role and timing of the polysaccharide in cell plate expansion and maturation. This study exemplifies the power of LLSM, combined with quantitative analysis to decode and untangle such a complex process. HighlightWe employed lattice light sheet 4D microscopy in plants to dissect cytokinesis, a multistage process involving orchestrating delivery of membranes and timely polysaccharide deposition. Robust quantitative analysis revealed distinct phase shifts, while inhibition of callose deposition abolished the phase transition.

plant biology↗

bioRxiv2023

Difference in Kernel Shape and Endocarp Anatomy Promote Dehiscence in Pistachio Endocarp

A fully split shell in pistachio (Pistacia vera) is a trait that is preferred by consumers and is a criterion in evaluating the grade of the pistachio nut. However, while the expanding kernel has been hypothesized to provide the physical force needed for shell split, the mechanisms that control shell split remains unknown. Furthermore, it is intriguing how the shell, or endocarp, splits at the suture ridge when there is no clear dehiscence zone. The objectives of this study were to 1) identify traits associated with dehiscence in fruit in the high split rate cultivar Golden Hills when compared to the lower split rate cultivar Kerman and determine the anatomical features associated with endocarp dehiscence at the suture region, and 2) examine the effect of kernel shape on endocarp dehiscence. We determined that despite of the fact that the pistachio endocarp is primarily composed of a single type of polylobate schlerenchyma cell, specialization of cell shape and size at the suture site results in smaller, more flattened cells. We report that there is a furrowing of the shell at the dorsal and apical suture site, where dehiscence initiates. This furrowing is not observed at the ventral suture site or in the indehiscent fruit of Pistacia atlantica, a species that has been used as rootstock for P. vera. In addition, the size of the kernel in the sagittal axis (the width) is strongly associated with higher split rate. Based on our results, a tentative model emerges where, in the absence of specialized cell types, cell shape modification can create an anatomically distinct region that is mechanically weak in the endocarp for the initiation of dehiscence, while the force from the width of the kernel is necessary for the shell split rate difference as observed in cultivars.

plant biology↗

bioRxiv2020

NMR spectroscopy analysis reveals an altered metabolic homeostasis in Arabidopsis seedlings treated with a cytokinesis inhibitor

In plant cytokinesis, de novo formation of a cell plate evolving into the new cell wall partitions the cytoplasm of the dividing cell. Cell plate formation involves highly orchestrated vesicle accumulation, fusion, and membrane network maturation supported by the temporary integration of elastic and pliable callose. The small molecule, Endosidin 7 (ES7) arrests late cytokinesis in Arabidopsis by inhibiting callose deposition at the cell plate. Its effect is specific, as it does not broadly affect endomembrane trafficking or cytoskeletal organization. It has emerged as a very valuable tool for dissecting this essential plant process. In order to gain deeper insights regarding its mode of action and the effects of cytokinesis inhibition on overall plant growth, we investigated the effect of ES7 through a nuclear magnetic resonance spectroscopy metabolomics approach. In this case study, profiles of Arabidopsis leaf and root tissues were analyzed at different growth stages and ES7 exposure levels. The results show tissue-specific changes in the plant metabolic profile across a developmental gradient, and the effect that ES7 treatment has on the corresponding metabolome. The ES7 induced profile suggests metabolic compensations in central metabolism pathways in response to cytokinesis inhibition. Further, this study shows that long-term treatment of ES7 disrupts the homeostasis of primary metabolism in Arabidopsis seedlings, likely via alteration of hormonal regulation.

biochemistry↗

bioRxiv2020

Callose deposition is essential for the completion of cytokinesis in the unicellular alga Penium margaritaceum

Cytokinesis in land plants involves the formation of a cell plate that develops into the new cell wall. Callose is a {beta}-1,3 glucan that transiently accumulates at later stages of cell plate development and is thought to stabilize the delicate membrane network of the cell plate as it expands. Cytokinetic callose deposition is currently considered specific to multicellular plant species as it has not been detected in unicellular algae. Here we present callose at the cytokinesis junction of the unicellular charophyte, Penium margaritaceum. Notably, callose deposition at the division plane of P. margaritaceum showed distinct, spatiotemporal patterns that could represent distinct roles of this polymer in cytokinesis and cell wall assembly. Pharmacological inhibition of cytokinetic callose deposition by Endosidin 7 treatment resulted in cytokinesis defects, consistent with the essential role for this polymer in P. margaritaceum cell division. Cell wall deposition and assembly at the isthmus zone was also affected by the absence of callose, demonstrating the dynamic nature of new wall assembly in P. margaritaceum. The identification of candidate callose synthase genes provides molecular evidence for callose biosynthesis in P. margaritaceum. The evolutionary implications of cytokinetic callose in this unicellular Zygnematopycean alga is discussed in the context of the conquest of land by plants. Summary StatementEvolutionarily conserved callose in Penium margaritaceum is essential for the completion of cytokinesis.

cell biology↗

bioRxiv2020

A Biophysical Model for Plant Cell Plate Development

Plant cytokinesis, a fundamental process of plant life, involves de novo formation of a cell plate that partitions the cytoplasm of the dividing cell. Cell plate formation is directed by orchestrated delivery, fusion of cytokinetic vesicles, and membrane maturation to the form the nascent cell wall by the timely deposition of polysaccharides such as callose, cellulose, and crosslinking glycans. In contrast to the role of endomembrane protein regulators the role of polysaccharides, in cell plate development is poorly understood. Callose, a {beta}-1-3 glucan polymer, is transiently accumulated during cell plate expansion to be replaced by cellulose in mature stages. Based on the severity of cytokinesis defects in the absence of callose, it has been proposed that it stabilizes this membrane network structure. However, there is currently no theory to understand its role in cytokinesis. Here we extend the Helfrich free energy model for membranes including a phenomenological spreading force as an "areal pressure" generated by callose and/or other polysaccharides. Regular cell plate development in the model is possible, with suitable bending modulus, for a two-dimensional late stage spreading force parameter of between 2-6pN/nm, an osmotic pressure difference of 2-10kPa, and spontaneous curvature between 0-0.04nm-1. With these conditions, stable membrane conformation sizes and morphologies emerge in concordance with stages of cell plate development. With no spreading force, the cell plate fails to mature properly, corroborating experimental observations of cytokinesis arrest in the absence of callose. To reach a nearly mature cell plate, our model requires the late stage onset that the spreading force coupled with a concurrent loss of spontaneous curvature. A simple model based upon production of callose as a quasi-two-dimensional self-avoiding polymer produces the correct phenomenological form of the spreading force, which will be further refined, since matching to our numbers requires an exceptionally high callose synthesis rate. Significance StatementPlant cell division features the development of a unique membrane network called the cell plate that matures to a cell wall which separates the two daughter cells. During cell plate development, callose, a {beta}-1-3 glucan polymer, is transiently synthesized at the cell plate only to be replaced by cellulose in mature stages. The role for this transient callose accumulation at the cell plate is unknown. It has been suggested that callose provides mechanical stability, as well as a spreading force that widens and expands tubular and fenestrated cell plate structures to aid the maturation of the cell plate. Chemical inhibition of callose deposition results in the failure of cell plate development supporting this hypothesis. This publication establishes the need for a spreading force in cell plate development using a biophysical model that predicts cell plate development in the presence and the absence of this force. Such models can potentially be used to decipher for the transition/maturation of membrane networks upon the deposition of polysaccharide polymers.

biophysics↗