Biology subjects

Signorelli, S.

Publications and source records attributed to Signorelli, S..

11 recordsLinked to original sources

bioRxiv2026

Optimizing light environment enables speed breeding in forage legumes: physiological limits and generation time reduction in Medicago sativa and Medicago truncatula

Climate change and increasing global demand for animal products are intensifying the need to accelerate genetic improvement of forage crops. Speed breeding (SB) has emerged as a powerful tool to shorten generation cycles; however, its application in perennial and autotetraploid forage legumes remains limited, particularly regarding reproductive performance and physiological constraints. Here, we optimized photoperiod, light intensity, and light quality to accelerate the life cycle of Medicago sativa (alfalfa) and its diploid relative Medicago truncatula under controlled conditions. We evaluated flowering, fruiting, seed harvest time, seed set, and germination across independent and combined SB treatments, and assessed photosynthetic performance to identify potential physiological trade-offs. Blue- red light supplementation, moderate-to-high irradiance (450 {micro}mol m-2 s-1), and extended photoperiods significantly accelerated reproductive development in both species, although optimal combinations differed between the diploid and autotetraploid backgrounds. A combined SB regime (20/4 h photoperiod at 450 {micro}mol m-2 s-1) reduced time to harvest by 17% in M. sativa and 28% in M. truncatula, while maintaining viable seed production. Chlorophyll fluorescence analysis revealed a higher photosynthetic plasticity in alfalfa compared with M. truncatula, indicating species-specific physiological limits to SB intensification. Our results establish practical SB conditions for alfalfa and an agronomically relevant M. truncatula genotype, providing an enabling platform to accelerate breeding cycles and trait evaluation in forage legumes.

plant biology↗

bioRxiv2025

Seasonal changes in the physiology and metabolism of grapevine perennating buds

Grapevine (Vitis vinifera L.) buds undergo seasonal dormancy to survive unfavourable conditions and synchronize growth with environmental cues. While dormancy transitions have been widely studied in temperate woody perennials, the physiological and metabolic dynamics underlying these transitions in grapevine remain poorly understood. Our study investigates seasonal changes in the physiology and metabolism of perennating buds in V. vinifera cv. Cabernet Sauvignon, focusing on dormancy depth, respiration, sugar metabolism, and cell cycle activity. We identified three distinct phases of bud quiescence: (i) para-dormancy (early summer), characterized by active metabolism and high levels of tricarboxylic acid cycle intermediates, shikimate, and myo-inositol; (ii) endo-dormancy (late summer to autumn), where dormancy depth peaked in late summer and was marked by reduced respiration and bud water content, and a sharp decline in hexose levels with a concomitant increase in raffinose; and (iii) eco-dormancy (winter to spring), featuring increased respiration, sugar mobilization (notably sucrose, glucose, and trehalose), and reactivation of cell division, with a shift of cells into the G2 phase. Just prior to bud burst, we observed a significant accumulation of sugar-phosphates, providing evidence that supports their role in promoting bud burst also in grapevine. Our findings provide new insights into the biochemical and physiological regulation of bud dormancy and bud burst, contributing to a deeper understanding of dormancy transitions in perennial crops.

plant biology↗

bioRxiv2025

Liquid-phase determination of Arabidopsis respiration and photosynthesis using Clark-type O2 electrodes

Photosynthesis and respiration are fundamental metabolic processes in plants, tightly connected through shared substrates, energy dynamics, and redox balance. Arabidopsis is the key genetic model for plants but monitoring these sorts of physiological processes presents significant challenges using traditional gas-exchange or fluorescence-based techniques due to the small size of intact Arabidopsis thaliana (arabidopsis) seedlings. Here, we validate and characterize the use of Clark-type oxygen electrodes, specifically the Hansatech Oxytherm+P system, to quantify both photosynthetic and respiratory activity in intact arabidopsis seedlings. By monitoring oxygen evolution in dark and light phases, we demonstrate that oxygen consumption and production correspond to mitochondrial respiration and photosynthesis, respectively. These processes were modulated by tissue biomass, light intensity, developmental stage, and stress conditions. Specific inhibitors such as potassium cyanide and paraquat confirmed that the recorded changes in oxygen concentrations reflected mitochondrial cytochrome oxidase activity and photosystem electron transport-dependent oxygen production, respectively. Moreover, oxygen evolution increased significantly with bicarbonate supplementation, validating the systems sensitivity to carbon fixation. We further showed that photosynthetic activity measured with this method correlates with a quantitative green index and responds dynamically to de-etiolation, abiotic stress (salt, osmotic, oxidative), and temperature shifts. Our study lays the groundwork for measuring photosynthesis based on oxygen evolution and respiration in arabidopsis knockout mutants, CRISPR lines, overexpression lines and ecotypes using Clark-type oxygen electrodes and highlights key considerations and limitations to consider when applying this approach. This platform could also be adapted for many other small tissue plant samples.

plant biology↗

bioRxiv2024

The physiology of bud dormancy and cell cycle status in grapevine

Evaluating the cell cycle status during dormancy of multicellular organisms is problematic. This is particularly so for woody perennial buds, where dormant and quiescent states are diffuse, and the organ may remain visibly unchanged for six to nine months of the year. In this study, we investigate cell cycle status of dormant grapevine buds by measuring mitotic index using an optimised method developed for grapevine bud tissue. The experimental material showed a dynamic range in the depth of dormancy, declining from 200 days in March to less than 60 days in May and 30 days in August, measured as the time to reach 50% bud burst in forcing conditions. Despite these differences, flow cytometry analysis showed that most nuclei isolated from these buds were arrested at the G1 phase. Ultrastructure analysis of the cells in the region of the shoot apical meristem confirmed that the mitotic activities of buds remained low at all time points, together with the development of starch grains and the relative absence of organelle development. HIGHLIGHTThe cell cycle and ultrastructure data suggest interesting evidence correspond to the growth resumption capacity of grapevine cv. Cabernet Sauvignon buds, i.e., absence of mitosis activities regardless of dormancy depth and starch accumulation irrespective of chilling accumulation.

plant biology↗

bioRxiv2023

Green Index: a widely accessible method to quantify greenness of photosynthetic organisms

Plant phenotyping involves the quantitative determination of complex plant traits using image analysis. One important parameter is how green plant tissues appear to the observer, which is indicative of their health and developmental stage. Various formulas have been developed to quantify this by calculating leaf greenness scores. We have developed a revised formula called "Green Index" (GI) devised out of the need to quantitatively assess how the apparent greenness of seedlings changes during de-etiolation. The GI calculation is simple, uses widely available RGB values of pixels in images as input, and does not require commercial software platforms or advanced computational skills. In this study we describe the conception of the GI formula, compare it with other widely used greenness formulas, and test its wider application in plant phenotyping using the open source free software platform RawTherapee. We demonstrate the utility of the GI in addressing common issues encountered in assessing plant biology experiments, underscoring its potential as a reliable and accessible tool. Finally, we explore the correlation between GI and chlorophyll content, assess its reliance on different types of photography, and summarizes the key steps for its effective utilization.

plant biology↗

bioRxiv2023

The Autophagy Receptor NBR1 Directs the Clearance of Photodamaged Chloroplasts

The ubiquitin-binding NBR1 autophagy receptor plays a prominent role in recognizing ubiquitylated protein aggregates for vacuolar degradation by macroautophagy. Here, we show that upon exposing Arabidopsis plants to intense light, NBR1 associates with photodamaged chloroplasts independently of ATG7, a core component of the canonical autophagy machinery. NBR1 coats both the surface and interior of chloroplasts, which is then followed by direct engulfment of the organelles into the central vacuole via a microautophagy-type process. The relocalization of NBR1 into chloroplasts does not require the chloroplast translocon complexes embedded in the envelope but is instead greatly enhanced by removing the self-oligomerization mPB1 domain of NBR1. The delivery of NBR1-decorated chloroplasts into vacuoles depends on the ubiquitin-binding UBA2 domain of NBR1 but is independent of the ubiquitin E3 ligases SP1 and PUB4, known to direct the ubiquitylation of chloroplast surface proteins. Compared to wild-type plants, nbr1 mutants have altered levels of a subset of chloroplast proteins and display abnormal chloroplast density and sizes upon high light exposure. We postulate that, as photodamaged chloroplasts lose envelope integrity, cytosolic ligases reach the chloroplast interior to ubiquitylate thylakoid and stroma proteins which are then recognized by NBR1 for autophagic clearance. This study uncovers a new function of NBR1 in the degradation of damaged chloroplasts by microautophagy.

cell biology↗

bioRxiv2022

Hydrogen Cyanamide Causes Reversible G2/M Cell Cycle Arrest Accompanied by Oxidation of the Nucleus and Cytosol in Arabidopsis thaliana Root Apical Meristem Cells

Hydrogen cyanamide (HC) is known to stimulate the production of reactive oxygen species (ROS) and also alter growth through modification of the cell cycle. However, the mechanisms by which HC alters cell proliferation and redox homeostasis are largely unknown. This study used roGFP2 expressing Arabidopsis seedlings to measure the oxidation states of the nuclei and cytosol in response to HC treatment. The Cytrap dual cell cycle phase marker system and flow cytometry were used to study associated changes in cell proliferation. HC (1.5mM) reversibly inhibited root growth during a 24h treatment. Higher concentrations were not reversible. HC did not synchronize the cell cycle. In contrast to hydroxyurea, HC caused a gradual accumulation of cells in the G2/M phase and decline of G1/S phase cells 16 to 24h post-treatment. This was accompanied by increased oxidation of both the nuclei and cytosol. Taken together, HC impairs proliferation of embryonic root meristem cells in a reversible manner through restriction of G2/M transition accompanied by increased oxidative poise.

plant biology↗

bioRxiv2021

Alternative oxidase1a and 1d limit proline-dependent oxidative stress and aid salinity recovery in Arabidopsis

A link between Pro catabolism and mitochondrial reactive oxygen species production has been established across eukaryotes and in plants increases in leaf respiration rates have been reported following Pro exposure. Here we investigated how alternative oxidases (AOXs) of the mitochondrial electron transport chain accommodate the large, atypical flux resulting from Pro catabolism and limit oxidative stress during Pro breakdown in mature Arabidopsis leaves. Following Pro treatment, AOX1a and AOX1d accumulate at transcript and protein levels, with AOX1d approaching the level of the typically dominant AOX1a isoform. We therefore sought to determine the function of both AOX isoforms under Pro respiring conditions. Oxygen consumption rate measurements in aox1a and aox1d leaves suggested these AOXs can functionally compensate for each other to establish enhanced AOX catalytic capacity in response to Pro. Generation of aox1a.aox1d lines showed complete loss of AOX proteins and activity upon Pro treatment, yet full respiratory induction in response to Pro remained possible via the cytochrome pathway. However, aox1a.aox1d leaves suffered increased levels of oxidative stress and damage during Pro metabolism compared to WT or the single mutants. During recovery from salt stress, when high rates of Pro catabolism occur naturally, photosynthetic rates in aox1a.aox1d recovered slower than WT or the single aox lines, showing that both AOX1a and AOX1d are beneficial for cellular metabolism during Pro drawdown following osmotic stress. This work provides physiological evidence of a beneficial role for AOX1a but also the less studied AOX1d isoform in allowing safe catabolism of alternative respiratory substrates like Pro. One sentence summaryThe alternative oxidase of plant mitochondria contributes to Pro catabolism by preventing oxidative stress in the electron transport chain and this aids recovery of leaf metabolic rates following salinity stress.

plant biology↗

bioRxiv2021

Autophagy promotes photomorphogenesis during seedling development in Arabidopsis in carbon limiting conditions

Autophagy is a conserved catabolic process that plays an essential role under nutrient starvation condition and influences different developmental processes. We observed that seedlings of autophagy mutants (atg2, atg5, atg7, and atg9) germinated in the dark showed delayed chloroplast development following illumination. The delayed chloroplast development was characterized by a decrease in photosynthetic and chlorophyll biosynthetic proteins, lower chlorophyll content, reduced chloroplast size, and increased levels of proteins involved in lipid biosynthesis. Confirming the biological impact of these differences, photosynthetic performance was impaired in autophagy mutants 12h post illumination. We investigated if the delayed chloroplast development could be explained by lower lipid import to the chloroplast or lower triglyceride (TAG) turnover. We observed that the limitations in the chloroplast lipid import imposed by trigalactosyldiacylglycerol1 are unlikely to explain the delay in photomorphogenesis. However, we found that lower TAG mobility in the triacylglycerol lipase mutant sugardependent1 significantly affected photomorphogenesis. Moreover, we showed that lower levels of carbon resources exacerbated the delay in photomorphogenesis whereas higher levels of carbon resources had an opposite effect. This work provides evidence that autophagic process operate during de-etiolation in a manner that contributes to photomorphogenesis through increasing lipid turnover to physically or energetically sustain photomorphogenesis.

plant biology↗

bioRxiv2021

The seasonal dynamics of bud dormancy in grapevine suggest a regulated checkpoint prior to acclimation

Grapevine (Vitis vinifera L.) displays wide plasticity to climate and seasonality, ranging from strongly deciduous to evergreen. Understanding the physiology of decisions to grow or quiesce is critical for improved crop management, prediction, and the adaptability of production to alternative climate scenarios. The perenniating bud (N+2) is a major economic unit and focus of study. Here we investigated the physiology and transcriptome of cv. Merlot buds grown in a temperate maritime climate from summer to spring in two consecutive years. The changes in bud respiration, hydration and internal tissue oxygen data were consistent with the transcriptome data. ABA-responsive gene processes prevailed upon the transition to a deep metabolic and cellular quiescence in the bud during autumn. Light, together with hypoxia and redox signalling presided over the resumption of nuclear and cellular growth in the transition to spring. Comparisons with transcriptome data from bud burst studies revealed a number of regulatory candidates for the orderly resumption of growth in spring, including components that may integrate light and temperature signalling. Importantly however, the bud burst forcing data, which is widely used as a measure of bud dormancy, were not consistent with the physiological and transcription data. We hypothesise the existence of a physiological checkpoint following bud set in summer, which if not met results in extreme quiescence. Collectively this is the most integrated developmental dataset of the latent bud of cultivated grapevine, and establishes a platform for systems approaches to study seasonal plasticity. One sentence summaryPhysiology and transcriptome data provide strong evidence of a regulatory checkpoint prior to acclimation and dormancy in latent grapevine buds.

plant biology↗

bioRxiv2018

Physiological regulation of bud burst in grapevine

The physiological constraints on bud burst in woody perennials, including the prerequisite for vascular development remain unresolved. Both light and tissue oxygen status have emerged as important cues for vascular development in other systems, however, light requirement appears to be facultative in grapevine, and the information related to the spatial variability of oxygen in buds is unclear. Here, we analysed apoplastic development at early stages of grapevine bud burst and combined molecular modelling with histochemical techniques to determine the pore size of cell walls in grapevine buds. The data demonstrate that quiescent grapevine buds were impermeable to apoplastic dyes (acid fuchsin and eosin Y) until after bud burst was established. The molecular exclusion size was calculated to be 2.1 nm, which would exclude most macromolecules except simple sugars and phytohormones. In vivo experiments show that grapevine buds were able to resume growth even following excision from the cane, and that the outer scales of grapevine buds may participate in the biochemical repression of bud burst. Furthermore, we demonstrate that the tissue oxygen partial pressure data correlated well with structural heterogeneity within the bud and differences in tissue density. These data consolidate evidence that the meristematic core becomes rapidly oxygenated during bud burst. Taken together, and when put in the context of earlier studies, these data provide solid evidence that the physiological and biochemical events that initiate bud burst reside within the bud, and question the role of long distance signalling in this developmental transition.\n\nHighlightsO_LIThe apoplastic pore size between the grapevine bud and the mother vine is dynamically regulated in the transition to bud burst.\nC_LIO_LIThe molecular exclusion size of the apoplastic connection between the bud and cane is calculated 2.1 nm prior to the initiation of bud burst.\nC_LIO_LIThe structural heterogeneity of the bud explains the spatial variance in tissue oxygen status, and the meristematic core is oxygenated during the initiation of bud burst.\nC_LIO_LILong distance maternal signals are not a requirement for bud burst.\nC_LI

plant biology↗